Epidemiology, Biochemistry and Molecular biology II Flashcards Preview

Question Bank MRCS A. > Epidemiology, Biochemistry and Molecular biology II > Flashcards

Flashcards in Epidemiology, Biochemistry and Molecular biology II Deck (62):
1

Which of the following is true regarding DNA structures?
(Please select 1 option)
Adenine (A) and guanine (G) are pyrimidine bases IncorrectIncorrect answer selected
Each amino acid is coded by one codon only
Each DNA strand has a pentose-phosphate backbone with projecting bases This is the correct answerThis is the correct answer
Guanine (G) always pairs with thymidine (T), and adenine (A) with cytosine (C)
There are 32 possible codons

Each DNA strand has a pentose-phosphate backbone with projecting bases

Pyrimidine bases are thymidine (T) and cytosine (C).

G always pairs with C and T with A.

Adenine (A) and guanine (G) are purine bases.

There are 64 possible codons, and each amino acid may be coded by more than one codon.

2

Which of the following techniques is used to identify isolated mRNA directly?
(Please select 1 option)
Denaturing gradient gel electrophoresis
Eastern blotting
Northern blotting
Southern blotting
Western blotting

Northern blotting

Western blotting is used to identify proteins whereas Southern blotting and denaturing gradient gel electrophoresis are used to identify DNA.

Eastern blotting identifies protein post translational modification and is an extension of western blotting.

3

Hypersensitivity
A Commonly found in blood transfusion reactions
B Deposition of immune complexes
C Hypersensitivity reaction is delayed
D Rapid onset following allergen exposure
Which type of hypersensitivity matches each description?
Type 1

Rapid onset following allergen exposure
Type 1 hypersensitivity is the principal mechanism underlying hay fever, asthma, and anaphylaxis. It is usually initiated by a rapid IgE response to an allergen in atopic individuals resulting from mast cell degranulation.

4

Hypersensitivity
A Commonly found in blood transfusion reactions
B Deposition of immune complexes
C Hypersensitivity reaction is delayed
D Rapid onset following allergen exposure
Which type of hypersensitivity matches each description?
Type 2

Commonly found in blood transfusion reactions

Type 2 responses result from antibody binding antigen on the cell surface and a resulting complement cascade. This is the mechanism commonly found in autoimmune disease and blood transfusion reactions.

5

Hypersensitivity
A Commonly found in blood transfusion reactions
B Deposition of immune complexes
C Hypersensitivity reaction is delayed
D Rapid onset following allergen exposure
Which type of hypersensitivity matches each description?
Type 3

Deposition of immune complexes

In type 3 hypersensitivity, immune complexes are formed or deposited, often in the walls of small blood vessels. This activates the complement cascade and recruits inflammatory cells.

Type 3 hypersensitivity is a key feature of autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus (SLE).

6

Hypersensitivity
A Commonly found in blood transfusion reactions
B Deposition of immune complexes
C Hypersensitivity reaction is delayed
D Rapid onset following allergen exposure
Which type of hypersensitivity matches each description?
Type 4

Hypersensitivity reaction is delayed
Type 4 hypersensitivity is delayed. It is mediated by T-lymphocytes which secrete cytokines and cause macrophage accumulation. These may develop into granuloma, causing progressive damage and fibrosis. Granulomas are features of sarcoidosis and Crohn's disease.

7

Which of the following statements regarding mortality rates is correct?
(Please select 1 option)
Crude mortality rates are calculated only from death certificate data
In males over the age of 15 years, age specific death rates increase by 10-20% over each subsequent five year period
Provide little important information about the changing pattern of disease in society
The standardised mortality ratio is the unexpected number of deaths divided by observed number of deaths for a specified group
They are usually standardised for age and sex

They are usually standardised for age and sex This is the correct answerThis is the correct answer
Mortality rates are a very important source of information about the changing pattern of disease in a country.

Most countries have a death certification system, and data from this source can be combined with population census information to calculate a crude mortality rate.

The crude mortality rate = deaths occurring over a one year period divided by the number in the population at midpoint of the year, multiplied by 1,000.

Mortality rates are better expressed as age specific death for males and females and are usually started at 15-19 years, and increased in five year intervals. There is little change in the age specific mortality rate between 15 and 34 years. After 45 years it approximately doubles over each five year period.

The standardised mortality ratio (SMR) is a ratio of expected deaths in an age group (calculated from age specific death rates) divided by the actual number of deaths in a specific group within that age group.

8

Which of the following is correct regarding immunoglobulin (IgG)?
(Please select 1 option)
Cannot cross the placenta to the fetus
Comprises one antigen-binding site and a site for the binding of complement
Constitutes approximately 25% of all immunoglobulins in a healthy individual
Has a Y-shaped molecular structure
Is secreted from T-lymphocytes

Has a Y-shaped molecular structure

Immunoglobulins (antibodies) are secreted from B-lymphocytes (plasma cells) in response to a specific antigen.

IgGs have a Y-shaped molecular structure. They are composed of two antigen-binding sites and a site for the binding of complement. Both antigen-binding sites are identical and consist of a long and heavy chain.

IgGs constitute approximately 75% of all immunoglobulins in a healthy individual.

Only IgGs can cross the placenta. This is important as they provide immune protection for the newborn in the first few months of life.

9

Which one of the following statements is correct?
(Please select 1 option)
The arithmetic mean is the measure to be preferred in data which are asymmetrically distributed
The geometric mean is always greater in value than the arithmetic mean
The median is also called the measure of central value
The standard deviation is a poor measure of dispersion
The value of the variable which occurs with the least frequency is the mode

The median is also called the measure of central value

The arithmetic mean is preferred in normal statistics as it generally represents the average.

The geometric mean is the nth root of the product of (a1 ... aN) and the arithmetic mean is (a1+ ...+aN)/N, hence the geometric mean will always be less than the arithmetic.

The standard deviation (SD) provides a good indication of distribution about the mean.

The mode represents the number occurring with greatest frequency.

10

Which of the following is true in statistics?
(Please select 1 option)
In a positively skewed distribution, the mean always lies to the left of the mode
In distributions which are markedly skewed, the arithmetic mean is a more appropriate measure than the geometric mean
In parametric data, the mode is usually different in value from the mean
The median is the most commonly occurring value
The standard deviation is also referred to as the root mean square deviation

The standard deviation is also referred to as the root mean square deviation This is the correct answerThis is the correct answer
In positively skewed data the mean usually lies to the right of the mode.

In skewed data, the geometric mean is the most appropriate measure.

Mode refers to the most frequently encountered value and in normally distributed data coincides with the mean and median values.

Standard deviation (SD) is the square root of the mean and is a measure of distribution of the data.

11

Which of the following is correct in significance testing?
(Please select 1 option)
A type I error is to reject the alternative hypothesis when it should be accepted
A type II error is to accept the alternative hypothesis when it should be rejected
The probability associated with a type I error is the significance level
The significance level is always set to 5%
The significance level is determined at the end of a significance test

The probability associated with a type I error is the significance level

The null hypothesis is that there is no difference between two groups. The alternative hypothesis is that there is a difference.

Rejecting the null hypothesis when there really is no difference between the two groups is a type 1 error.

Accepting the null hypothesis (rejecting the alternative hypothesis) when there is a difference is a type 2 error.

Rejection of the null hypothesis depends on the probability-significance level, which is usually at p

12

Which one of the following statements concerning statistical tests is true?
(Please select 1 option)
Correlation coefficients vary between -10 and +10
k is the symbol denoting coefficient of correlation
Student's t-test is a non-parametric test
Wilcoxon's rank test needs equal sample sizes
y = a + bx is a regression equation

y = a + bx is a regression equation This is the correct answerThis is the correct answer
The variance of correlation coefficients is between −1 and +1.

r is the symbol denoting coefficient of correlation.

Student's t-test is parametric.

y = a + bx is the equation of a straight line.

13

Which of the following is true in breast cancer?
(Please select 1 option)
Mutations of the p53 gene are protective
The susceptibility gene BRCA1 confers a risk of over 95% by age 70
The susceptibility gene BRCA2 decreases the risk of male breast cancer
There is a recognised association with ataxia telangiectasia
Up to 50% of new cases have an inherited basis

There is a recognised association with ataxia telangiectasia
Mutations of the p53 gene on chromosome 17p12 are implicated in some inherited and also sporadic forms of breast cancer.

BRCA1 confers a risk of 83% for breast cancer and 63% for ovarian cancer. There is a modest increase in risk for colon and prostate. The BRCA1 gene is on chromosome 17q21.

BCRA2 confers the same risk as BRCA1 for breast cancer in women and is less involved in ovarian cancer. The BRCA2 gene is on chromosome 13q12.

The AT gene on chromosome 11q22 is thought to play an important role in breast cancer, accounting for up to 13% cases in some reports.

In the United Kingdom up to 10% of new cases have an inherited basis which is equivalent to over 1,000 women per year.

14

A report of a clinical trial of a new post-operative analgesic reads:
"In a comparison between the new drug and a placebo, a higher proportion of patients taking the new drug obtained relief from pain (p
Which of the following statements is correct?
(Please select 1 option)
Amongst 100 patients treated with the drug, five would be expected to have a placebo response
The probable error of the observations is +/- 5%
The result may have occurred by chance alone in less than one in five occasions
The result should be regarded as reaching conventional levels of statistical significance
The trial was well designed

The result should be regarded as reaching conventional levels of statistical significance

It would be false to say that amongst 100 patients treated with the drug five would be expected to have a placebo response. The placebo effect is often higher - of the order or 20-30%.

'Probable error' is meaningless; standard error is derived from the variance.

It is true that the result may have occurred by chance alone in less than one in 20 occasions. This is the meaning of the 'p value'. 0.05 = 1/20.

It is also true that the result should be regarded as reaching conventional levels of statistical significance. p

15

Regarding statistics, which one of the following is true?
(Please select 1 option)
The incidence tells how common a situation is
The prevalence tells how often a situation occurs
The reliability of a test is defined as the relevance of the test to the activities being treated
The sensitivity of a test is the probability of the test being positive in somebody with the condition
The specificity of a test is the probability of a positive test given the absence of the condition

The sensitivity of a test is the probability of the test being positive in somebody with the condition
The prevalence tells how common a situation is, not the incidence.

The incidence tells how often a situation occurs, not the prevalence.

The relevance of the test to the activities being treated is the validity. Reliability is the ability of a test to produce the same result when repeated under identical conditions.

16

With regard to statistics which one of the following is true?
(Please select 1 option)
SD = SEM/√n
The SD equals the SEM in non-parametric tests
The SD is a measure of observation variability
The SEM determines the accuracy of measurement of the observations
The standard deviation (SD) is less than the standard error of the mean (SEM)

The SD is a measure of observation variability

SEM = SD/√n

SEM is the standard deviation of all the means of large random samples of size n from a given population. It is of central importance in significance testing.

If testing to see if there is a difference between two population means (for example, t-test) then
t = mean/SEM.

17

Which of the following is true of achondroplasia?
(Please select 1 option)
Can lead to lumbar lordosis
Individuals have proportionate trunk and limb lengths
Individuals usually have decreased mental development
Is usually a sporadic condition
x Rays shows short dense bones with narrowing of the ends

Can lead to lumbar lordosis

Achondroplasia is usually a hereditary condition but may also occur sporadically.

It particularly affects the pre-bone cartilage of long bones at birth resulting in dwarfism. The affected individuals have a normal trunk length but short stumpy limbs all of the same length. They also have a large head with a saddle nose.

Adult dwarfs have increasing lumbar lordosis, bow legs, and shortened proximal arms and legs.

Intelligence level is usually normal, though there may be delayed motor development and complications of hydrocephalus.

x rays show short dense bones with flared ends with wide epiphysis.

18

Increased numbers of chromosomes occur in which of the following?
(Please select 1 option)
Fragile-X syndrome
Jacobsen syndrome
Klinefelter's syndrome
Turner's syndrome
Retinoblastoma

Klinefelter's syndrome

Human cells have 23 pairs of chromosomes, giving a total of 46 per cell.

In Turner's - XO (that is, X instead of XX or XY) resulting in underdevelopment of female sexual characteristics.

Fragile X syndrome (Martin-Bell syndrome) results from an elongation of the X chromosome causing intellectual, emotional and behavioral features which range from severe to mild in manifestation.

Jacobsen syndrome results from a deletion of the terminal 11q causing mild mental retardation, with poor expressive language skills.

In Klinefelter's syndrome (XXY) the affected men are usually sterile, and tend to have longer arms and legs and to be taller than their peers.

Retinoblastoma results from a mutation on the RB1 gene on chromosome 13 causing a rapidly developing cancer of the retina.

19

A random selection of 1200 adults agree to participate in a study of the possible effects of drug X.
They are followed prospectively for a period of five years to see if there is an association between the incidence of cataract and the use of drug X.
Which type of study is this?
(Please select 1 option)
Case-control study
Cohort study
Cross-over study
Cross-sectional study
Randomised controlled clinical trial

Cohort study

Cohort studies or longitudinal studies involve the follow up of individuals.

A cohort study may be prospective in which individuals who are exposed and non-exposed to a putative risk factor are followed up over a defined period of time and the disease experience of the exposed group at the end of follow up is compared with that of the non-exposed group.

A cohort study may also be historical (retrospective or non-concurrent). A cohort is identified, for whom records of exposure status are available from the past, and whose disease experience can now be measured, a substantial period of time having already elapsed since exposure.

20

For the data series: 2, 1, 6, 4, 2, which of the following statements is true?
(Please select 1 option)
The mean is 3
The mean is always identical to the median
The median is 3
The mode is 4
The standard deviation is 4

The mean is 3
The mean is the average of the group, the median is the middle of the series with the mode being the most common data point.

The standard deviation is 1.78 (it is definitely not 4 as that would encompass the entire range of the numbers).

The mode is 2 and the median is 2.

21

Which of the following statements regarding blood groups and blood products is untrue?
(Please select 1 option)
Group O and rhesus negative is the universal donors blood
Stored blood becomes progressively more acidotic and hyperkalaemic with time
Stored blood contains a normal amount of clotting factors
Stored whole blood contains dextrose, phosphate and citrate
The ABO system is inherited in an autosomal dominant pattern

Stored blood contains a normal amount of clotting factors

The universal donors blood is blood group O.

The universal recipient is blood group AB.

Red blood cells (RBCs) are the blood component most frequently used for transfusion. A transfusion of RBCs increases the amount of oxygen that can be carried to the tissues of the body.

RBCs that have been separated from the liquid plasma (packed RBCs) should be administered to patients who have anaemia or who have blood loss. The plasma contains the clotting factors.

22

Which of the following is correct in statistics?
(Please select 1 option)
A normally distributed population, 95 per cent of the values fall in the range of the mean plus or minus one standard deviation
Standard error and standard deviation (SD) are synonymous
The chi-squared test applies only to parametric data
The statement "p is less than 0.01" means that there is less than 1% likelihood of an event having occurred by chance
Variance is equal to the square-root of the standard deviation

The statement "p is less than 0.01" means that there is less than 1% likelihood of an event having occurred by chance

Mean plus or minus 2 SDs encompasses 95% of normally distributed observations.

Variance is the square of the SD.

SEM=root mean square SD.

Chi-squared test assesses proportions and does not depend upon normality.

Statistical significance is usually accepted at the p

23

The prevalence rate of a disease has which one of the following features?
(Please select 1 option)
It cannot be estimated from a cross-sectional study
It cannot be used to determine the health needs of a community
It is independent of the duration of illness
It is independent of the incidence of the disease
It measures all the current cases in the community

It measures all the current cases in the community This is the correct answerThis is the correct answer
It is dependent on the number of individuals who contract the disease in a particular time period.

Because it looks at the number of individuals with a disease at a given point in time or within a defined interval, if a patient has recovered from the illness in that duration then they would not be included in the prevalence rate, because it is expressed as a proportion.

As cross-sectional studies are effectively a snap shot they can be used to estimate the proportion of people with a disease at that time and thus the point prevalence.

Prevalence is one measure that can assess the health needs of a community.

24

In a normal (Gaussian) distribution, which of the following is correct?
(Please select 1 option)
68% of observations lie between the mean 2 standard deviations
95% of observations lie between the mean 2 standard errors
Data from a normal distribution are suitable for non-parametric tests without prior transformation
The 95% confidence interval may be calculated as the mean ±1.96 times the standard error of the mean for population >30
The mean, median and mode do not coincide

The 95% confidence interval may be calculated as the mean ±1.96 times the standard error of the mean for population >30

The mean and median of a normal distribution are equal.

The probability that a normally distributed random variable, x, with mean, σ, and standard deviation, μ, lies between (σ - 1.96μ) and (σ + 1.96σ) is 0.95.

The probability that a normally distributed random variable, x, with mean, σ, and standard deviation, μ, lies between (σ-μ) and (σ+ μ) is 0.68.

Ninety five per cent of the distribution of sample means lies within 1.96 standard deviations of the population mean.

A parametric test is a hypothesis test that makes certain distributional assumptions about the data that they are Gaussian.

25

In clinical trials, which of the following is true?
(Please select 1 option)
Errors are more common when big samples are used
Type I error is more likely to occur when multiple t tests are used
Type I error is wrongly accepting the null hypothesis
Type II error is accepting the null hypothesis when it is valid
Type II error is increased by the use of a confidence interval

Type I error is more likely to occur when multiple t tests are used

We reject the null hypothesis if our P-value is less than the significance level, that is, that is, p

26

Which of the following is true of meta-analysis of randomised controlled trials?
(Please select 1 option)
Gives conclusion making further controlled trials unnecessary
Is usually performed if individual trials are considered to have used flawed methods
Provides a more stable estimate of the effect of treatment than individual trials
Should include trials in which patient selection is not randomised
Should only include peer-reviewed studies

Provides a more stable estimate of the effect of treatment than individual trials

Meta-analyses combine the results from individual studies to produce an estimate of the overall effect of interest.

The individual studies do not have to be peer reviewed.

By looking at the effects of numerous small trials, the direction and magnitude of the average effect with an associated confidence interval, allows treatment effects with greater power and precision to be detected.

This would lead to quality differences as the study designs should be similar. This is the main reason for doing a meta-analysis.

It gives conclusions with both high power and precision to estimate effects but also leads to questions that further controlled trials need to address.

27

Which of the following is true of a 95 % confidence interval (CI)?
(Please select 1 option)
Can only be used in parametric data
Is a test of the null hypothesis
Is calculated at ± 1.96 times the standard error of the mean
Is not useful when comparing data with another population
If zero difference lies within the 95% when comparing two groups to a treatment, it indicates the treatment is not effective

Is calculated at ± 1.96 times the standard error of the mean

Ninety five per cent confidence intervals can be used for both distributional and distribution-free data.

A 95% confidence interval looks at the range of values within which we are 95% confident that the true population parameter lies.

Therefore, using the above formula, if we were to repeat the experiment many times the interval would contain the true population mean on 95% of occasions.

Confidence intervals increase the accuracy when comparing means with another population by looking at the spread of differences. A wide confidence interval indicates that the estimate is imprecise and if the 95% CI crosses zero, which is the value of no difference, then it indicates that the treatment has no effect.

28

In a longitudinal study a questionnaire assesses joint symptoms in a population.
The response to the baseline examination of the population sample was 75%. However, 30% of those examined were subsequently lost to follow-up.
Which one of the following statements is correct?
(Please select 1 option)
The incidence of arthritis may be underestimated in this study
The incomplete response at entry and follow-up introduces information bias
The power of the study to assess the association between physical activity and incidence of musculoskeletal problems is unaffected by incomplete follow-up
The prevalence of arthritis will be overestimated in this study
The prognosis of joint disease can be reliably assessed from this study

The incidence of arthritis may be underestimated in this study

Information bias relates to the way questions within the questionnaire may be worded or the way subjects are provided with information concerning the trial which may influence the way they respond.

As the response to the questionnaire is not complete, then potentially both the incidence and the prevalence of arthritis may be underestimated.

Again, the power is reduced due to the loss of follow-up data.

Prognosis cannot be determined from this type of study which is more an assessment of prevalence/incidence

29

Which one of the following is untrue of chromosomes?
(Please select 1 option)
23 Chromosomes are found in germinal cells
In female only one X chromosome is activated
Klinefelter's syndrome result from an extra X chromosome in male
The Barr body is due to inactivated X chromosome
There are 23 pairs of autosomal chromosome traits

There are 23 pairs of autosomal chromosome traits This is the correct answerThis is the correct answer
There are 22 pairs of autosomal chromosomes and one pair of sex chromosomes.

Due to meiosis only 23 chromosomes are found in the germinal cell.

A female has two X chromosomes but only one is activated and the other stays dormant as the Barr body.

In Klinefelter's syndrome the male cell has an extra X chromosome.

30

Which of the following describes the observation that occurs with the greatest frequency?
(Please select 1 option)
Correlation
Mean
Median
Mode
Variance

Mode

The mode is the observation that occurs with the greatest frequency.

The mean is the average of the data, and the median is the middle observation value.

The variance is the spread of the observations.

31

If a characteristic is normally distributed in a population:
(Please select 1 option)
there will be equal numbers who have more or less of the characteristic than the mean
the median value will be greater than the mean
ten percent of individuals will be beyond two standard deviations from the mean
the mode will not equal to the median
this means that most of the population is composed of normal individuals

there will be equal numbers who have more or less of the characteristic than the mean

In a normally distributed population the values will be symmetrical distributed about the mean and as a consequence the median equals the mean and mode. Five percent of individuals will be beyond two standard deviations from the mean in a normal distribution.

32

When evaluating a report of a clinical trial, which of the following is correct?
(Please select 1 option)
Control and treatment groups must be equivalent in size
If randomisation is conducted properly, chance differences are inevitable
Inadequate sample size has been shown to produce true positives and true negatives
Results are invalid if the trial is not of double blind construction
Withdrawal of patients from a trial by the investigator does not lead to bias

If randomisation is conducted properly, chance differences are inevitable

The interpretation of data is a frequently asked question in the examinations.

Results of all trials may be valid irrespective if they are double blind or not. However, inaccuracies can occur due to too small a sample size.

Again, bias may arise due to the withdrawal of selective patients and this may be positive or negative.

The size of groups need not necessarily be (and seldom are) equal for meaningful results.

33

Which of the following is true regarding carcinoma of the pancreas?
(Please select 1 option)
Has a better prognosis than ampullary adenocarcinoma
Is less common in smokers
Is most commonly situated in the body of the pancreas
Is not associated with chronic pancreatitis
Rarely causes pancreatic calcification

Rarely causes pancreatic calcification This is the correct answerThis is the correct answer
"Risk factors for the development of pancreatic cancer include smoking cigarettes, obesity, diabetes and chronic pancreatitis."

34

Which of the following is correct concerning the standard deviation of a group?
(Please select 1 option)
Is the square of the variance
Is a valid statistical parameter for observations that have a skewed distribution
Is numerically lesser than the standard error of the mean
Can be used for the calculation of chi square
Is a measure of the scatter of observations about the mean

Is a measure of the scatter of observations about the mean This is the correct answerThis is the correct answer
A . It is the square root of the variance.

B. It applies only to normal distribution.

C. It is numerically greater; standard error = standard deviation divided by square root of n.

D. Chi square compares proportions.

35

In a set of values which of the following is correct?
(Please select 1 option)
Having a normal distribution, approximately 95% of the values will lie within the range between (mean +2 standard deviations) and (mean - 2 standard deviations)
Having a skewed distribution, the arithmetic mean, the mode and the median are equal
Of a normally distributed variable, the probability of attaining a value higher than two standard deviations above the mean is approximately 1 in 4 (p = approx. 0.25)
The median is the value that occurs the most frequently
The mode is that point on the scale of measurement above which lie exactly half the values and below which lie the other half

Having a normal distribution, approximately 95% of the values will lie within the range between (mean +2 standard deviations) and (mean - 2 standard deviations)

The mode is the value that occurs the most frequently.

The median is that point on the scale of measurement above which lie exactly half the values and below which lie the other half.

Having a normal distribution the arithmetic mean, the mode and the median are equal.

Of a normally distributed variable, the probability of attaining a value higher than two standard deviations above the mean is approximately 1 in 40 (p = approx. 0.025).

36

Which of the following is correct regarding familial adenomatous polyposis?
(Please select 1 option)
Has an increased incidence of ampullary carcinoma
Is an autosomal recessive condition
Is associated with colonic carcinoma in 100% of individuals by age of 40 years
May be associated with peripheral nerve tumours
The gene is found on chromosome 21

Has an increased incidence of ampullary carcinoma

Familial adenomatous polyposis has an increased incidence of ampullary carcinoma, hence the need to follow up even after total colectomy.

It is an autosomal dominant condition.

It is associated in almost all, but not 100% of individuals with colonic carcinoma. It may also be associated with CN tumours. Gardner's syndrome is associated with soft tissue tumours.

The gene is found on chromosome 5q 21-22d - Turcot's syndrome.

37

Which of the following is correct in comparing confidence intervals with P values?
(Please select 1 option)
95% confidence intervals are equivalent to a P value of 0.95
As the sample size decreases, the confidence interval will decrease
Confidence intervals refer to the target population
The confidence interval is approximately equal to the standard deviation
The P value measures how clinically significant a statistical result is

Confidence intervals refer to the target population

Estimation procedures can be of two types:

Point estimates
Interval estimates
The sample mean (x) is a logical point estimate of the population with a mean of u.

The confidence interval gives a measure of the true mean u lying between two values.

The 95% confidence interval is defined as: mean +/- 1.96 × the standard error of the mean.

The standard error of the mean equals the population variance o /(N)0/2. The standard error of the mean therefore decreases as the population sample increases. The confidence intervals therefore decrease as the population sample increases.

Unfortunately, statistical significance does not equate with clinical significance. For example, a doubling of risk from 0.0001% to 0.0002% may be completely insignificant, even though it is statistically highly significant.

38

A cohort study suggests a statistical link between drinking a specific local herbal tea and the development of oesophageal cancer.
Which one of the following would suggest that the link is causative?
(Please select 1 option)
An odds ratio of 2:1
The finding of a number of different histological types ofoesophageal carcinoma in the cluster
The finding of similar odds ratios for osteoarthritis in thesame environment
The finding of similar results in a number of studies
The finding that increasing consumption is associated with adecreased rate of disease

The finding of similar results in a number of studies

Criteria for assessing causation include:

Strength: strong associations are more likely than weak ones.
Consistency: multiple studies finding the same thing are more likely to be causal.
Specificity: if a variable is associated with a single outcome, and the outcome is associated with only a single possible cause, then the relationship is more likely to be causal.
Temporality: causes must precede effects. This is absolutely necessary to suggest causation.
Biological gradient: if an increased exposure is associated with an increased rate or severity of disease, then causality is more likely.
Plausibility: hypotheses should sound reasonable. However, new epidemiological findings may expand knowledge.
Coherence: causal association is strengthened if epidemiological data fit in with pathology.
Experiment: if the cause is removed and disease frequency declines, the likelihood of a causal link is strengthened.
Analogy: if a similar association has been shown to be causal, then the association under investigation is more likely to be causal.

39

In a case-control study, 10/127 patients in the exposed group, and 4/253 in the unexposed group developed the condition.
Which one of the following would be the standard methods of reporting the results?
(Please select 1 option)
Mean, standard deviation, and 95% confidence intervals
Median, range, and interquartile ranges
Odds ratio and standard error
Rate and 95% confidence interval
Risk difference and 95% confidence interval

Risk difference and 95% confidence interval This is the correct answerThis is the correct answer
Measurements may be continuous or categorical and single or two group.

Continuous data:

Single group:
Normally distributed: mean standard deviation, 95% confidence interval
Non-normal: median, range, interquartile range
Two groups:
mean difference, 95% confidence interval
Categorical:

Single group:
rate (risk), 95% confidence interval
Two groups:
Risk difference, 95% confidence interval
Relative risk, 95% confidence interval
Odds ratio, 95% confidence interval
The relative risk is the rate of one compared with the rate of the other. The odds ratio is calculated from data collected in a case-control study.

40

Which of the following is correct if a characteristic is normally distributed in a population?
(Please select 1 option)
20% of individuals will be more than two standard deviations from the mean
The mean will be less than the mode
The median will be less than the mean
The numbers of individuals above and below the mean will be equal
This implies that most of the population are normal individuals

The numbers of individuals above and below the mean will be equal

About 5% of individuals will be more than two standard deviations from the mean

In a normal distribution the mean, mode and median are all equal.

If the numbers of individuals above and below the mean are not equal then the distribution is said to be skewed.

The word 'normal' has a different meaning - it refers to 'The Normal Law' of Poincare and the mathematics of Abraham de Moivre. De Moivre described the 'normal curve of error' in 1733 which described natural phenomena such as errors in astronomical observations and gambling with dice. Normal distribution does not mean that individuals are normal as one might say that height is normally distributed - there is no 'normal' height but there is an average height.

41

A middle-aged lady who is being investigated for abdominal pain 'accidentally' has a nutritional profile taken instead of basic electrolyte estimation and this reveals an elevated magnesium level.
Her only medical history is of chronic constipation for which she has been self-medicating with Epsom salts.
What is the likely cause of her abnormal magnesium?
(Please select 1 option)
Acute pancreatitis
Bowel preparation
Diarrhoea
Laxatives
Malabsorption

Laxatives

Long term treatment with Epsom salts (magnesium sulphate), a popular over the counter preparation, may lead to hypermagnesaemia.

The other four options, which are not uncommon scenarios in general surgical practice, all lead to lower than desired magnesium levels.

42

A 58-year-old man undergoes a liver resection for a colorectal metastasis.
On the second postoperative day he was noted to be hypophosphataemic despite having a normal phosphate level pre-operatively.
What is the likely cause?
(Please select 1 option)
Enteral nutrition
Haemolysis
Hepatic failure
Ischaemic bowel
Renal failure

Hepatic failure

Hypophosphataemia is a common finding after liver resection in patients with normal renal function.

It was believed that the low phosphate was due to hepatic regeneration but recent evidence now suggests that it is due to renal loss (hyperphosphaturia), although the mechanism is uncertain.

In hepatic failure alkaline phosphatase levels are also elevated.

The other options all cause elevated levels of phosphate.

43

The following laboratory results were returned in a 6-week-old boy admitted with six days of severe projectile vomiting:
pH 7.51 (7.36-7.44)
PO2 12 KPa/95 mmHg (11.3-12.6)
PCO2 4.7 KPa/35 mmHg (4.7-6.0)
Blood Urea 11 mmol/L (2.5-7.5)
Na+ 131 mmol/L (137-144)
K+ 3 mmol/L (3.5-4.9)
Chloride 83 mmol/L (95-107)
Which of the following is true concerning this patient?
(Please select 1 option)
An x ray of the abdomen is likely to show dilated loops of small bowel
He has respiratory alkalosis
He is likely to have a bulging anterior fontanelle
He should be commenced immediately on half strength soy protein, low lactose formula
He should be resuscitated immediately with normal saline

He should be resuscitated immediately with normal saline This is the correct answerThis is the correct answer
He has a metabolic, rather than respiratory alkalosis as CO2 is not reduced. He is likely to have a sunken fontanelle as he is very dehydrated.

Pyloric stenosis would highly likely because of the age and hypochloraemic, hypokalaemic metabolic alkalosis.

He should be resuscitated with normal saline first.

Dilated bowel would not be expected, as pyloric rather than small bowel obstruction is present.

44

A 44-year-old man was involved in a head on car crash at 70 mph during which his car burst into flames.
On admission he has a BP 96/65 mmHg; heart rate 130/min regular and has oliguria. After initial resuscitation his injuries are noted to be: 40% burns; compound fracture of the left tibia; and fracture dislocation of the right hip.
His baseline investigations of note include:
Hb 7.5 g/dL (13.0-18.0)
pH 7.1 (7.36-7.44)
Potassium 6.1 mmol/L (3.5-4.9)
Which of the following is an explanation for his potassium level?
(Please select 1 option)
Insulin therapy
Rhabdomyolysis
Steroid therapy
SIADH
Vomiting

Rhabdomyolysis

A multiply injured patient may be hyperkalaemic due to tissue injury (burn or crush) as a result of potassium being released from cells.

If hypotensive for a prolonged period there is a risk of acute tubular necrosis and if there is rhabdomyolysis the myoglobinuria may lead to acute renal failure.

45

Combined salt and water depletion is not associated with which of the following?
(Please select 1 option)
Fall in the central venous pressure (CVP)
High blood urea concentration
Low concentration of sodium in the urine
High urine specific gravity (SG)
Pre-renal uraemia

Low concentration of sodium in the urine

Combined salt and water depletion would result in generalised dehydration (hypovolaemia) with equal depletion of total, extracellular and intracellular fluid volume and a low central venous pressure (CVP).

The consequence of this dehydration would be an effort to concentrate the urine and hence relatively high sodium concentration in a concentrated urine of high SG and osmolality. Blood urea, sodium and potassium concentrations are likely to be elevated with an elevated haematocrit.

46

Which of the following is true regarding bilirubin?
(Please select 1 option)
Conjugates iron
Facilitates absorption of carbohydrate from the gut
Is a steroid
Is bound to albumin in the circulation
Is conjugated to glycerine

Is bound to albumin in the circulation

Bilirubin is not synthesised from cholesterol (like the steroids) but is a break down product of haem metabolism. When red cells and haemoglobin are broken down in the reticuloendothelial system the iron is re-utilised. The tetrapyrrole ring of haemoglobin is broken down to bilirubin.

Myoglobin is another source of bilirubin. Unconjugated bilirubin forms 95% of bilirubin in the circulation. It is not water soluble (unlike conjugated bilirubin) and is bound to albumin. Bilirubin is conjugated in the liver, mainly with glucuronic acid. Conjugated bilirubin is secreted into the biliary canaliculi.

47

Which of the following are not correctly paired?
(Please select 1 option)
Conn's syndrome and metabolic alkalosis
High altitude and respiratory acidosis
Pancreatic fistula and metabolic acidosis
Shock and metabolic acidosis
Uretero-colic anastomosis and hyperchloraemic acidosis

High altitude and respiratory acidosis

Conn's syndrome (hyperaldosteronism) produces an alkalosis due to potassium/hydrogen exchange.

Altitude sets up over breathing with a respiratory alkalosis.

Pancreatic fistula causes loss of bicarbonate and a metabolic acidosis.

All types of shock result in reduced tissue perfusion causing lactic acidosis.

48

Which of the following is normally in a higher concentration outside the cell than in the intracellular fluid?
(Please select 1 option)
Adenosine monophosphate (AMP)
Adenosine triphosphate (ATP)
Magnesium
Potassium
Sodium

Sodium This is the correct answerThis is the correct answer
The following are found in higher concentrations intracellularly than extracellularly:

Potassium
Magnesium
ATP
Adenosine diphosphate (ADP)
AMP
Phosphate

49

Regarding fluid balance, which of the following statements is true?
(Please select 1 option)
0.9% sodium chloride solution contains no free water and is thus restricted to the extracellular compartment
After intravenous administration of crystalloids, the distribution of these fluids throughout the body depends on its osmotic activity
In patients with pathological capillary leakage, the oncotic pressure becomes decreasingly important in determining fluid fluxes
The intracellular fluid volume is insensitive to changes in the sodium concentration of the extracellular fluid
The microvascular endothelium separating interstitial fluid from the intravascular compartment is freely permeable to water

After intravenous administration of crystalloids, the distribution of these fluids throughout the body depends on its osmotic activity

Oncotic pressure becomes a distinct problem when capillary leakage occurs as in dependent oedema or ascites.

The intracellular sodium concentration is exquisitely sensitive to the extracellular sodium with osmosis resulting in shifts in water between the compartments.

The microvascular endothelium is not freely permeable to water and relies upon a number of processes including osmosis.

50

Which of the following is true of hypernatraemia?
(Please select 1 option)
Commonly causes arrhythmias
May be associated with intra-abdominal haemorrhage
May be caused by trans-urethral resection of prostate (TURP) syndrome
May cause seizures
Sodium levels should be corrected rapidly

May cause seizures

Hypernatraemia is defined as a sodium over 145 mmol/l.

Arrhythmias do not commonly occur.

Causes of hypernatraemia can be sub-divided into

Water loss, for example, diarrhoea, vomiting, diuresis, diabetes insipidus
Reduced water intake, for example, altered thirst, impaired access
Excessive sodium intake, for example, salt tablets, hypertonic saline, hyperaldosteronism.
Hypernatraemic patients are usually dehydrated, and the effects of hypernatraemia are mainly on the central nervous system (seizures) and muscle function. Cerebral dehydration with rupture of the vessels and intracranial haemorrhage may occur.

TURP syndrome is usually associated with hyponatraemia.

Rapid correction of the serum sodium may lead to cerebral oedema and convulsions, and full correction should take at least 48 hours.

51

Which of the following is a cause of hyponatraemia?
(Please select 1 option)
Cirrhosis
Conn's syndrome
Cushing's syndrome
Diabetes insipidus
Hypertonic saline

Cirrhosis

Assessment of the volaemic status of the patient allows the causes of hyponatraemia to be sub-divided into three categories:

Euvolaemia, for example, syndrome of inappropriate anti-diuretic hormone (SIADH), high water intake, hypothyroidism.
Hypovolaemia, for example, diarrhoea, vomiting, diuretics, renal tubular dysfunction.
Hypervolaemia, for example, cirrhosis, heart failure.
Diabetes insipidus and the administration of hypertonic saline cause hypernatraemia.

Mineralocorticoid excess, due to a disease state such as Conn's syndrome or Cushing's syndrome, results in hypernatraemia.

52

Which of the following is correct regarding carcinoembryonic antigen?
(Please select 1 option)
Is a tumour marker exclusively for colorectal carcinoma
Is elevated in nearly 45% of patients with Duke's A disease
Is not useful to detect tumour recurrence after treatment
Is positive in 100% of patients with distant or liver metastasis (Duke's D)
May be elevated in ulcerative colitis

May be elevated in ulcerative colitis This is the correct answerThis is the correct answer
Carcinoembryonic antigen is a tumour marker which indicates the presence of certain types of cancer in humans. It is normally found in the fetus but is elevated in adults in the presence of colorectal cancer or some other types of cancer, such as

Breast
Thyroid
Lung
Ovary
Pancreas
Stomach.
Serum carcinoembryonic antigen is elevated in fewer than 5% of patients with Duke's A colorectal cancer, about 25% of Duke's B, 44% of Duke's C, and about 65% in distant metastasis.

Apart from cancers, the levels of carcinoembryonic antigen may be elevated in some conditions such as

Benign liver disease
Inflammatory disorders of the GI tract (ulcerative colitis)
Renal impairment
Smoking.
Elevated levels of carcinoembryonic antigen in the blood indicate the occurrence, presence or recurrence of the tumour. It is thus used in the early stages of diagnosis and treatment, to monitor the effect during treatment, and as a follow-up tool to establish the disease-free status or to identify early recurrence.

53

Combined salt and water depletion is associated with which of the following?
(Please select 1 option)
A low blood urea concentration
A low concentration of sodium in the urine
A low urine specific gravity
An increase in the central venous pressure
Pre-renal uraemia

Pre-renal uraemia This is the correct answerThis is the correct answer
Combined salt and water depletion would result in generalised dehydration with equal depletion of total, extracellular and intracellular fluid volume: low central venous pressure (CVP).

The consequence of this dehydration would be an effort to concentrate the urine and hence relatively high sodium concentration in a concentrated urine of high specific gravity (SG) and osmolality.

Blood urea, sodium and potassium concentrations are likely to be elevated with elevated haematocrit.

54

Which of the following is true regarding bilirubin?
(Please select 1 option)
Conjugates iron
Facilitates absorption of fat from the gut
Is a steroid
Is conjugated to glycerine
Is unbound in the circulation

Facilitates absorption of fat from the gut

Bilirubin is not synthesised from cholesterol (like the steroids) but is rather a break down product of haem metabolism.

It is toxic to tissue, and therefore in the blood is transported bound to albumin.

It is responsible for the emulsification of fats and facilitates their absorption from the gastrointestinal tract.

55

Which of the following statements regarding intravenous solutions is correct?
(Please select 1 option)
0.18 saline in 4.0% dextrose is appropriate for the initial management of an infant with signs of peripheral circulatory failure
Normal saline contains 180 mmol/l of sodium
Normal saline with added potassium is appropriate therapy to correct a non-respiratory alkalosis
Ringer's lactate solution is designed for intracellular fluid replacement
Sodium bicarbonate 8.4% is a hypo-osmolar solution

Normal saline with added potassium is appropriate therapy to correct a non-respiratory alkalosis

Normal saline contains 154 mmol/l of sodium.

Ringer's solution is also known as Hartmann's solution. It is a crystalloid and contains 131 mmol/l of sodium and 111 mmol/l of chloride. It is ideally balanced.

In an extracellular loss, such as diarrhoea or haemorrhage, sodium falls and therefore administration of a hyponatraemic solution may further compound the problem. Ringer's is more appropriate.

Sodium bicarbonate 8.4% is a hyperosmolar solution with an osmolarity of approximately 2,000 mOsmol/l.

0.18% saline in 4% dextrose is also called dextrose saline. It is a crystalloid containing 30 mmol/l of sodium and 30 mmol/l Cl.

A child showing signs of hypovolaemia or signs of a peripheral circulatory collapse needs to be resuscitated, preferably with plasma expanders. These include colloid fluids such as blood or plasma. They exert an oncotic pressure and thus retain fluid in the circulating volume.

Crystalloid fluids containing iso- or hypotonic concentrations of sodium do not remain in the plasma volume following IV administration. The volume of distribution of these fluids is extracellular and thus only provides a short term expansion of the circulating volume.

Normal saline with additional potassium is used in the correction of metabolic alkalosis.

56

Which of the following is true regarding a solution of 0.18% sodium chloride and 4% dextrose?
(Please select 1 option)
Contains 4 g of dextrose per 1,000 ml
Contains 72 mmol of sodium per litre
Contains 160 calories per litre
Is appropriate intravenous therapy for a child who has hypernatraemic dehydration secondary to gastroenteritis
Is the fluid of choice in the treatment of diabetic ketoacidosis

Contains 160 calories per litre

0.18% saline in 4% dextrose is also called dextrose saline. It is a crystalloid containing 30 mmol/L of sodium and 30 mmol/L Cl. It contains 160 calories per litre and has 4 g dextrose per 100 ml.

In diabetic ketoacidosis the fluid of choice is normal saline, although if there are signs of shock or pre-shock then colloid is preferable in the initial stages of resuscitation.

Correction of the dehydration takes place over 36-48 hours.

57

Metabolic acidosis results from which of the following?
(Please select 1 option)
Gluttonous intake
Pyloric stenosis
Sulphonylureas
Thiazide diuretics
Uraemia

Uraemia This is the correct answerThis is the correct answer
Pyloric stenosis is an important cause of metabolic alkalosis.

SulMetabolic acidosisphonylureas (e.g. glicazide) do not cause a metabolic acidosis. Biguanides (e.g. metformin), however, are associated with lactic acidosis in patients with severe hepatic or renal impairmant.

Thiazide diuretics can cause metabolic alkalosis.

Uraemia is a well recognised cause of metabolic acidosis although the precise mechanism is unclear. It may be related to the diversion of glutamate metabolism to the liver and the consequent bicarbonate consuming effect of hepatic ureagenesis.1

58

Which of the following is true of prostate cancer?
(Please select 1 option)
Incidence is approximately 50 per 100,000 of the population
Is commoner in Asian than Caucasian men
Is commoner in Caucasian men than Afro-Caribbeans
Is the most common cause of cancer death
Risk increases from the age of 40 for those with a first degree relative with the

Risk increases from the age of 40 for those with a first degree relative with the condition This is the correct answerThis is the correct answer
Prostatic carcinoma is commonest cause of cancer in males but due to effective treatment is the second commonest cause of death from cancers next to lung malignancy.

Risk increases from the age of 50 for those without a family history but from 40 for those with a first degree relative with the condition and Afro-Caribbeans where risk is greatest. Asians have the least risk.

About 10% have a family history and the incidence is between 10-20 per 100,000.

59

Which one of the following is not an essential amino acid?
(Please select 1 option)
Arginine
Lysine
Methionine
Tryptophan
Valine

Arginine

The nine essential amino acids, particularly important when considering nutrition, are

Valine
Tryptophan
Lysine
Leucine
Isoleucine
Phenylalanine
Threonine
Methionine and
Histidine.

60

Following a major operation in a normal person, which of the following is true?
(Please select 1 option)
Decreased heart rate
Decreased metabolic rate
Fall in blood glucose concentration
Fluid retention
Potassium retention

Fluid retention

The stress response and increased cortisol levels result in a relative hyperglycaemia, together with a tachycardia.

Fluid retention is frequently seen post-surgery, and potassium loss is seen.

The metabolic rate is raised.

61

Which one of the following statements is true concerning body water in a 70 kg man?
(Please select 1 option)
Distribution depends on osmolar content of various compartments CorrectCorrect
Extracellular fluid is approximately 28 litres
Intracellular fluid is approximately 14 litres
Plasma volume is 7 litres
Total body water is approximately 55 litres

Distribution depends on osmolar content of various compartments

Total body water is roughly 50-60% of body weight, so this man's TBW would be roughly 40 litres.

Of this extracellular water would be roughly a third with intracellular fluid making up 2/3.

Obviously, the distribution of body water is affected by the osmolality (protein concentrations both intra- and extracellularly).

62

In which of the following is increased serum prostate specific antigen (PSA) seen?
(Please select 1 option)
In pancreatitis
After a digital rectal examination
In transitional cell cancer of the bladder
In renal failure
Only when there is extracapsular spread in prostate cancer

After a digital rectal examination

PSA is prostate specific not prostate cancer specific.

In benign prostatic hyperplasia (BPH) 25% have PSA > 4.0 ng/ml and 8% have PSA > 10 ng/ml.

PSA is not raised even in end stage renal failure1. It can be raised in all stages of prostate cancer.