Epidemiology, Biochemistry and Molecular biology Flashcards Preview

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Flashcards in Epidemiology, Biochemistry and Molecular biology Deck (63):
1

A term referring to systematic inaccuracy.

Bias refers to systematic inaccuracy due either to consistent over-recording or under-recording and is usually due to recorder bias which may be subconscious.

2

The proportion of those who do not have the disease that are correctly identified as negative.

Specificity
Sensitivity relates to the test's ability to identify positive results. Where a test has a high sensitivity it is has few false negatives.

Specificity relates to the ability of the test to correctly identify negative results. A test with high specificity has few false positives. If a test with high specificity is positive, that person is likely to have the disease because of the low false positive rate.

Therefore, in order to detect genuine positives (to indicate disease), we need a test with high specificity rather than a high sensitivity.

3

A type 1 error.

False positive
Type 1 error is the incorrect rejection of the null hypothesis (that there is no difference between groups) and may also be interpreted as a 'false positive' observation, that is, you say that there is a difference when there is not.

Error is any random source of inaccuracy. For example an error collecting variable, leading to a less precise estimate.

4

A random source of inaccuracy.

Error

Bias refers to systematic inaccuracy due either to consistent over-recording or under-recording and is usually due to recorder bias which may be subconscious.

Error is any random source of inaccuracy. For example an error collecting variable, leading to a less precise estimate.

5

A type 2 error.

False negative

A type 1 error is a false positive and a type 2 error is a false negative.

6

Ability to exclude a true negative.

Specificity

The terms sensitivity and specificity can be applied to statistical tests as well as to clinical and biological tests. The probability of picking up a genuine positive result is the sensitivity of the test whereas the probability that the test can indicate a true negative result is the specificity of the test.

7

Which is the most abundant immunoglobulin in the plasma?
(Please select 1 option)
IgA
IgD
IgE
IgG
IgM

IgG

IgG makes up 70-80% of plasma immunoglobulin. IgG plays an important role in toxin neutralisation and bacterial opsonisation.

IgA appears selectively in seromucous secretions, tears, sweat and breast milk and fuctions by inhibiting the binding of organisms to mucosal surfaces and prevents them entering cells.

IgD is present only in small amounts in plasma and is possibly involved in the control of B cell activation.

IgE is found in minute amounts in plasma and binds to mast cells.

IgM is the first type of immunoglobulin formed after initial antigen contact.

8

A 38-year-old lady is admitted with cellulitis surrounding a traumatic wound.
She has never taken penicillin previously. She is placed on intravenous flucloxacillin and benzylpenicillin. Shortly after the second dose she becomes acutely short of breath and collapses.
She is resuscitated successfully after administration of intravenous adrenaline.
What type of reaction has this lady experienced?
(Please select 1 option)
Type I hypersensitivity
Type II hypersensitivity
Type III hypersensitivity
Type IV hypersensitivity
Type V hypersensitivity

Type I hypersensitivity

This lady has had an anaphylactic reaction.

This is a type I reaction and is mediated by the binding of the antigen and IgE on mast cells; other examples would include latex allergy, and non-anaphylactic type I reactions include asthma and allergic rhinitis.

Type II reactions involve antibody to cell-bound antigen causing cell destruction, for example, haemolysis following blood transfusion.

Type III reaction results from deposition of immune complexes in tissues, for example, acute post-streptoccoal glomerulonephritis.

Type IV reactions are caused by T lymphocytes which react with antigen producing a delayed hypersensitivity reaction, for example, Heaf test for in immunised individuals.

9

A 48-year-old lady presents complaining of restlessness, weight loss and tremor.
On examination she is found to have warm, sweaty and shaky hands. She is in atrial fibrillation. Eye examination reveals exopthalmos and lid-lag. Thyroid examination demonstrates a smooth goitre. She also has pre-tibial myxoedema. Thyroid fucntion tests (TFTs) show a low level of TSH and elevated T3 and T4.
What is the most likely diagnosis?
(Please select 1 option)
De Quervain’s thyroiditis
Graves’ disease
Hashimoto’s disease
Multinodular goitre
Toxic solitary adenoma

Graves’ disease

This ladies TFTs show hyperthyroidism.

Graves' disease is the most common cause of thyrotoxicosis and occurs as a result of the development of antibodies raised against the thyroid-stimulating hormone (TSH) receptor.

De Quervain's thyroiditis and Hashimoto's disease are causes of hypothyroidism.

Both a toxic solitary adenoma and a multinodular goitre can cause hyperthyroidism (although most multinodular goitres are non-toxic) but do not cause the eye signs.

10

Which cells secrete antibodies?
(Please select 1 option)
B lymphocytes
Memory cells
Neutrophils
Plasma cells
T lymphocytes

Plasma cells

Antigen binding leads to B lymphocytes activation and the formation of antibody-secreting plasma cells.

11

Which immunoglobulin forms pentamers?
(Please select 1 option)
IgA
IgD
IgE
IgG
IgM

IgM

IgM molecules are pentameric structures formed from five basic monomer units.

IgA molecules are dimers.

12

This Kaplan-Meier curve provides information regarding the survival in months of two patient groups who received two different oncological therapies.
Which of the following can be concluded from this plot?
(Please select 1 option)
Significantly improved survival is seen in group 1 following five months of treatment
Survival probability is improved with treatment in group 1
Survival probability is improved with treatment in group 2
There is a significantly improved survival associated with therapy in group 1 versus group 2
There is no significant difference in survival between the two groups

Survival probability is improved with treatment in group 1

Kaplan-Meier curves represent the proportion of the study population still surviving (or free of disease, or reaching the designated study endpoint) at successive times.

One cannot infer information regarding statistical significance without an actual calculation and although there appears a clear difference between these two groups, group size may be small and hence the differences in survival may not necessarily be different.

The only thing that one may confidently state regarding the above graph is that survival was increased more in group 1 than group 2. It may or may not be statistically significant.

13

A 35-year-old shop worker presents with pain in her calves which develops after 50 yards of walking. The pain settles with rest.
On examination she has yellow discolouration of her palmar creases.
Her fasting lipid profile reveals:
Cholesterol 9.6 mmol/L (

Type III hyperlipidaemia

Remnant hyperlipidaemia (type III hyperlipidaemia) is associated with:

Hypercholesterolaemia, typically 8-12 mmol/L
Hypertriglyceridaemia, typically 5-20 mmol/L
Normal ApoB concentration
Palmar xanthomata - orange discoloration of skin creases
Tuberoeruptive xanthomata - elbows and knees
Early onset of cardiovascular disease
Early onset of peripheral vascular disease.
Remnant hyperlipidaemia is due to abnormal function of the ApoE receptor, which is normally required for clearance of chylomicron remnants and IDL from the circulation.

The receptor defect causes levels of chylomicron remnants and IDL to be higher than normal in the blood stream. The receptor defect is an autosomal recessive mutation or polymorphism.The genotype of the homozygous condition is apo E-2/E-2 and occurs with a frequency of 1:100.

Hypoalphalipoproteinaemia is a rare, familial condition and is associated with low HDL.

Chylomicronaemia is associated particularly with hypertriglyceridaemia and not with large elevations in cholesterol.

Familial hypercholesterolaemia is due to LDL-receptor deficiency, and is not associated with elevated triglyceride levels.

14

A researcher compared the mean scores for nausea on a rating scale between standard therapy and a new drug in the treatment of chemotherapy induced nausea.
Which one of the following is the most appropriate statistical test?
(Please select 1 option)
Chi square test
Life table analysis (log rank test)
Paired t test
Pearson correlation
Unpaired t test

Unpaired t test This is the correct answerThis is the correct answer
The two sample unpaired t test is used to test the null hypothesis that the two populations corresponding to the two random samples are equal.

For a paired t test, the data are dependent, that is, there is a one-to-one correspondence between the values in the two samples; for example, the same subject measured before and after a process change, or the same subject measured at different times.

15

A clinical investigation examined the effectiveness of a new test for diagnosing pancreatic carcinoma. The sensitivity was reported as 70%.
Which one of the following statements is correct?
(Please select 1 option)
70% of people will be correctly classified as having or not having the disease
70% of people with a normal test result will not have the disease
70% of people with an abnormal test result will have the disease
70% of people with the disease will have a normal test result
70% of people with the disease will have an abnormal test result

70% of people with the disease will have an abnormal test result This is the correct answerThis is the correct answer
Sensitivity is the conditional probability that the test will be positive if the condition is present.

Specificity is the conditional probability that the test will be negative if the condition is absent.

Therefore, interpreting the data there is a 70% probability of the test being positive when tested in a group of patients with the disease.

16

A newborn is noted to have an umbilical hernia.
Which of the following is associated with umbilical hernia?
(Please select 1 option)
Congenital hypoparathyroidism
Down syndrome
Infants of diabetic mothers
Post-term delivery
Turner's syndrome

Down syndrome

Umbilical hernias occur more frequently in infants of Afro-American descent, premature babies and females.

The vast majority of umbilical hernias are not related to any disease condition.

However, umbilical hernias can be associated with rare diseases, such as:

Mucopolysaccharide storage diseases
Beckwith-Wiedemann syndrome
Down syndrome, and
congenital hypothyroidism.

17

Which of the following is a polygenic disorder?
(Please select 1 option)
Ankylosing spondylitis
Erythropoietic porphyria
Fragile X syndrome
Huntington's disease
Pendred’s syndrome

Unlike the other conditions, no one specific genetic defect has been identified to account for ankylosing spondylitis.

Hungtindon's chorea is an autosomal dominant condition.

Fragile X syndrome is due to a trinucleatide repeat at the FMR 1 gene on the X chromosome.

Erythropoietic porphyria is an autosomal recessive condition as is Pendred's syndrome.

18

A publication assesses a new diagnostic test for thyroid cancer.
Which of the following terms would reflect the number of cases of thyroid cancer correctly identified by this new test?
(Please select 1 option)
Accuracy
Negative predictive value
Positive predictive value
Sensitivity
Specificity

Sensitivitiy

The specificity of a test is the probability that a test will produce a true negative result when used on an unaffected population.

The sensitivity of a test is the probability that it will produce a true positive result when used on an affected population (as determined by a reference or "gold standard").

The positive predictive value of a test is the probability that a person is affected when a positive test result is observed.

The negative predictive value of a test is the probability that a person is not affected when a negative test result is observed.

Accuracy is expressed through the above four parameters.

19

A new antiplatelet agent has been proven to reduce the risk of stroke in a year from 10% in patients treated with conventional treatment to 6% in patients treated with conventional treatment plus the new agent.
The cost of this new drug is £100 per month.
How much extra would a hospital need to spend over the course of a year to prevent one stroke?
(Please select 1 option)
£1,200
£6,000
£18,000
£30,000
£100,000

£30,000

The 'absolute risk reduction' is 10% − 6% = 4%.

The 'number needed to treat' to prevent a stroke therefore equals 100/4 = 25.

25 patients would need to be treated at a cost of £100/month for 12 months to prevent a stroke which gives the total cost as £30,000.

20

In a trial of a new drug the following results were obtained:
Improved Not improved
Treatment group 44 16
Placebo group 36 26
Which of the following statements regarding the statistical analysis or interpretation of the trial is true?
(Please select 1 option)
A Student's t test could be used
Pearson's co-efficient of linear regression would be an appropriate significance test
The data could be evaluated using the chi square test
The numbers are too small to draw any conclusions
The results so obviously show the benefit of treatment that statistical analysis is not required

The data could be evaluated using the chi square test

These data would be ideal for a chi square test. It is a 2 × 2 contingency table for which there is a special chi squared formula that gives a value that can be looked up in a table giving the p value.

The Student's t test cannot be used as we are comparing proportions not means.

Pearson's co-efficient cannot be calculated as there is no linear regression to plot.

Nothing is ever so obvious that no statistical analysis is needed.

21

Apoptosis is induced by which of the following?
(Please select 1 option)
Activation of caspases
Antibodies
DNA synthesis
Necrosis
The MAP kinase pathway

Activation of caspases

A key event in the initiation of apoptosis is the activation of a cascade of cysteine-aspartate specific proteases known as caspases.

22

A cohort study of 7,500 patients aimed to find out whether the use of olive oil in cooking has an impact on cardiovascular disease.
Approximately half the patients used olive oil in cooking and half used animal fat.
Which of these is a disadvantage of a cohort study?
(Please select 1 option)
It is not possible to measure the incidence/risk of a disease
They are not suitable when exposure to risk factors is rare
They are susceptible to recall bias; there is a differential ability of patients to remember exposure to a risk factor
They can only provide information about one outcome
When the outcome of interest is rare a very large sample size is needed

When the outcome of interest is rare a very large sample size is needed This is the correct answerThis is the correct answer
A cohort study takes a group of individuals and follows them for a period of time, the aim being to study whether the exposure to a particular aetiological factor has any effect on the incidence of disease.

As such they are relatively time consuming and expensive to perform. Advantages include being able to study exposure factors that are rare and being less susceptible to recall bias than case-control studies.

They are also able to measure the incidence/risk of a disease.

Results are usually expressed as the relative risk of developing the disease given exposure to the aetiological factor.

23

A trial is proposed to see whether excess alcohol use is a risk factor for osteoporosis.
It is decided to perform a case-control study rather than a cohort study.
Which of these is an advantage of a case-control study?
(Please select 1 option)
It can provide information on a wide range of outcomes
It is expensive to perform
It is possible to measure the incidence of a disease directly
It is possible to study diseases that are rare
The time sequence of events can be assessed

It is possible to study diseases that are rare

A case-control study compares the characteristics of a group of patients with the disease with a control group of patients who do not have the disease.

Advantages of case-control studies are that:

They are particularly suitable for rare diseases
A wide range of risk factors can be investigated
There is no loss to follow up
They are relatively cheap and quick to perform.
Results are usually quoted as an odds ratio.

24

In a double blind controlled trial assessing the impact of a new antihypertensive in the treatment of stroke versus conventional antihypertensive therapy in the secondary prevention of stroke, the authors report an absolute annual risk reduction in the incidence of stroke of 0.5%.
The cost of the new treatment is £100 more expensive per patient per year than conventional therapy.
What would be the cost of implementing the new therapy for each stroke prevented?
(Please select 1 option)
£2000
£4000
£10,000
£20,000
£50,000

£20,000

In this case, the annual incidence of stroke is reduced by 0.5% and treatment is £100 more than conventional therapy.

Thus for every 200 patients treated one less stroke would occur with the new drug versus the conventional therapy.

Number needed to treat (NNT) is therefore 200 per year to prevent one stroke.

Thus the annual cost of this treatment associated with preventing one stroke would be:

200 patients × £100 = £20,000.

25

An experienced group of surgeons report on a randomised placebo-controlled trial comparing a particular carotid surgery technique to a sham operation.
Their study concludes that 'using this advanced surgical technique reduces the risk of stroke from 4.3% to 3.8% (p .
What has this study proved about the surgical procedure?
(Please select 1 option)
Acceptability
Effectiveness
Efficacy
Safety
Usefulness

Efficacy

This is an experienced group of vascular surgeons working in ideal conditions. Similar studies have been reported for carotid surgery but it has been difficult to prove their usefulness outside areas of expertise.

It is often difficult to generalise the findings in a study group to everyday practice.

Efficacy = the effect of something under ideal or laboratory conditions.
Effectiveness = the effect of something in the real world.

26

Which of the situations listed is most likely to invalidate the following statistical tests?
A study compares two interventions for the treatment of chronic foot ulceration. Comparisons between the average healing times are to be made using the unpaired Student's t test.

Non-normal distribution of data

Non-normal distribution of data
Certain assumptions are required for appropriate interpretation of statistical analyses.

In particular, t tests and ANOVA require that the data should have a normal/Gaussian distribution and the tests are invalid if the data are non-parametric, whereas alternative tests such as the Mann-Whitney U test or the Wilcoxon signed rank tests are appropriate. These latter tests can be used for normally distributed data but their ability to reject the null hypothesis accurately is impaired.

Small sample size would not invalidate test results, as it would be less likely to show differences between groups but the results would still be valid.

Similarly, small SDs and narrow confidence intervals would increase the likelihood of demonstrating a difference but have no effect on validity of the test.

The composition of the groups really makes no difference.

27

A study analyses change in body composition over time before and after intensive care. Results are to be analysed using analysis of variance (ANOVA).

Non-normal distribution of data
Certain assumptions are required for appropriate interpretation of statistical analyses.

In particular, t tests and ANOVA require that the data should have a normal/Gaussian distribution and the tests are invalid if the data are non-parametric, whereas alternative tests such as the Mann-Whitney U test or the Wilcoxon signed rank tests are appropriate. These latter tests can be used for normally distributed data but their ability to reject the null hypothesis accurately is impaired.

Small sample size would not invalidate test results, as it would be less likely to show differences between groups but the results would still be valid.

Similarly, small SDs and narrow confidence intervals would increase the likelihood of demonstrating a difference but have no effect on validity of the test.

The composition of the groups really makes no difference.

28

A randomised placebo control study of a new cholesterol-lowering drug is performed. Patients with a cholesterol of 5.0 - 6.0 are recruited into the study. The mean cholesterol level of each group at three months is compared.

Paired t test
t Tests are significant tests used to compare the means of two different groups.

Paired or independent (unpaired) t tests are appropriate depending on the study design. Paired data are usually measurements taken in the same group of subjects before and after some treatment or intervention. The number of degrees of freedom for the paired t test is n -1, where n is the number of pairs.

29

A randomised placebo control study of a new drug for intermittent claudication is performed. The maximum walking distance (for each patient) at the start of the trial is subtracted from their walking distance at the end of the study. Individual results are compared between the two groups.

Mann-whitney U test

The Mann-Whitney U-test is a significance test for comparing the distribution of a given variable between two groups. This test is a non-parametric alternative to the independent t test. In this case the data from the two independent groups can be ranked and compared.

30

A review of patients who have undergone colonic resection for cancer and have been given a blood transfusion in the post-operative period are compared with those who have not been given a transfusion to assess if recurrence of the cancer is higher in either group.

Chi squared test

The Chi-squared (X2) is a significance test for comparing two or more proportions from independent groups. When carrying out the Chi-squared test for trend, the observed frequencies are displayed in a contingency table, and the expected frequencies calculated. These are then compared with the null hypothesis.

31

A 17-year-old female developed insulin dependent diabetes mellitus. Her uncle and grandmother also had diabetes mellitus.

Polygenic
There is no specific mode of inheritance associated with diabetes mellitus. The inheritance is therefore considered polygenic - many genes contributing rather than one single gene defect. There are a few rare exceptions such as the DIDMOAD syndrome (diabetes insipidus, diabetes mellitus, optic atrophy and nerve deafness) (Wolfram syndrome) which is an autosomal recessive condition.

32

A 4-year-old male child presents with mild jaundice, pallor and a palpable spleen tip. His father has had a work up for anaemia.

Autosomal dominant
This child has hereditary spherocytosis, which has an autosomal dominant inheritance pattern.

33

A 14-year-old boy presents with increasing instability, ataxia and tremor with recurrent respiratory and sinus infections. On examination he has prominent capillaries on his sclerae.

Autosomal recessive
This male has the typical features of ataxia telangiectasia. It is a rare disorder of childhood that occurs in about 1/40,000 and 1/100,000 persons worldwide.

The ailment is progressive. By their teens, patients with AT are frequently wheelchair-bound.

34

A 4-year-old boy developed swelling of his left knee with trivial injury. He had similar episodes like this before. His grandfather had the same disease.

X-linked recessive
This boy's case is typical of haemophilia A or possibly B (Christmas disease).

Haemophilia A often presents at a young age with spontaneous bleeding into a joint. The level of factor VIII (A) or IX (B) in the blood determines the severity of haemophilia. Factor levels of less than 1-2% are found in subjects with severe haemophilia, and they experience spontaneous bleeds into joints or muscles.

Both are X-linked recessive inheritance.

35

An 18-year-old female underwent caries tooth extraction and developed profuse bleeding. On history she revealed menorrhagia. Her mother and her grandfather had the same disease.

Autosomal dominant
This young woman with a bleeding tendency following a dental procedure, together with menorrhagia, suggests von Willebrand disease. This disease is due to a deficiency of von Willebrand factor and is inherited in an autosomal dominant pattern with variable penetrance most commonly, but rarely can be recessive.

von Willebrand's disease is the most common hereditary bleeding disorder. It affects both sexes approximately equally. Most cases are mild, and bleeding may occur after a surgical procedure/tooth extraction. It is also associated with menorrhagia.

36

In a study of 950 subjects with a BMI below 25 kg/m2, a new serological marker for coeliac disease was assessed against the gold standard test of jejunal biopsy.
The following results were obtained:
Test positive Test negative
Biopsy positive 40 10
Biopsy negative 60 840
What is the sensitivity of this test?
(Please select 1 option)
40%
55%
66%
80%
93%

80%

Sensitivity relates to the probability that the person with a disease will be correctly identified with the disease. Therefore, in this study, 50 subjects have the disease, of whom 40 are correctly identified with the disease giving a sensitivity of 80%.

The specificity is the probability that a person without the disease will be correctly identified by the test. In this case, there are 900 subjects without the disease of whom 840 were identified by the test - giving a specificity of 93%.

This is perhaps best illustrated by annotating the table used in the question:

Test positive Test negative
Biopsy positive 40 (True Positives) 10 (False Negatives)
Biopsy negative 60 (False Positives) 840 (True Negatives)
Sensitivity = True Positives / (True Positives + False Negatives) = 40/(40+10) = 80%

Specificity = True Negatives / (True Negatives + False Positives) = 840/(840+60) = 93%

37

In a study of the treatment of elderly patients with atrial fibrillation the findings were:
Subjects receiving warfarin (n= 6000): 6% had strokes or died as a consequence of stroke over the three year study period.
Subjects treated with aspirin (n = 8000): 9% had stroke or death from a stroke over the three year study period.
The risk of stroke in the untreated (placebo) subjects (n = 6000) with atrial fibrillation over the three year study period was 12%.
Which of the following percentages is the approximate annual incidence of stroke in the treated population in this study?
(Please select 1 option)
2.6%
3.3%
5.5%
6.9%
7.7%

2.6%

One needs to calculate the incidence as follows:

In the group treated with warfarin there were 360 strokes (6% of 6000).

In the aspirin treated group there were 720 strokes (9% of 8000).

Thus, there are 1080 strokes amongst the treated population (n=14000) over a three year time period.

Therefore there are 360 strokes annually in the treated group (14000) giving an annual incidence of stroke of approximately 2.6%.

Note: remember to divide by three since the study lasted three years and the figures given are for the three years incidence rates.

38

The upper and lower limit of normal, of a biochemical test in the hospital laboratory, is two standard deviations of the population. What percentage of the population is represented by 2 standard deviations?
(Please select 1 option)
85%
95%
97%
99%
99.7%

95%

If one assumes that there is a normal distribution of this test in the population, then one standard deviation includes 68% of the population, 2 standard deviations include approximately 95% of the population; 3 standard deviations include 99.7% of the population.

39

Immunological function is not characteristically suppressed by which of the following?
(Please select 1 option)
Antimetabolites
Corticosteroids
Fulminant sepsis
Ionising radiations
The presence of a low platelet count in the blood

The presence of a low platelet count in the blood This is the correct answerThis is the correct answer
Immune function is suppressed by:

Steroids
Antiproliferative agents (which affect white cell generation)
Ionising radiation
Fulminant sepsis
Tumours (leukaemia but other solid cancers too)
Malnutrition deficiency.
Neither anaemia nor thrombocytopenia has any effect on immune function.

40

Which of the following is true of the thymus?
(Please select 1 option)
Descends anterior to the brachiocephalic vein
Develops from the fourth pharyngeal pouch
Is made up of cells of ectodermal origin
Lies within the posterior mediastinum
Increases in size with age

Descends anterior to the brachiocephalic vein

The thymus is a lymphatic organ that develops mainly from the endoderm of the third pharyngeal pouch.

Some of the epithelial cells become the thymic (Hassall's) corpuscles; others form a network of epithelial reticular cells believed to secrete the thymic hormones that are linked to differentiation of T lymphocytes.

The developing thymus descends in front of all the major structures of the neck to enter the anterior mediastinum.

It doubles its size rapidly after birth and stays the same size throughout the life but the lymphoid components decrease with age. However, the secretion of thymic hormones and its effect on lymphocytes that migrate to it continue throughout life.

41

Concerning DNA structure, which of the following statements is correct?
(Please select 1 option)
Adenine pairs with cytosine
Each nucleotide pair includes two purines
Genetic information is transferred from nuclear DNA to ribosomes by tRNA
Pairs of nucleotides form bonds between the two strands of the DNA double helix
Uracil differs from cytosine by one ribose sugar

Pairs of nucleotides form bonds between the two strands of the DNA double helix

The structure of deoxyribonucleic acid (DNA) is an antiparallel double helix. Hydrogen bonds between complementary base pairs hold the two strands together.

Nucleic acids are classified as purines (adenine and guanine) and pyrimidines (cytosine and thymine). In DNA adenine and thymine form one pair and guanine and cytosine form the other.

In ribonucleic acid (RNA) thymine is replaced by uracil. Uracil can be formed by deamination of cytosine.

Information is transferred from nuclear genomic DNA to ribosomes by messenger RNA (mRNA). Transfer RNA (tRNA) is involved in translation of mRNA into a polypeptide.

42

A baby with left congenital diaphragmatic hernia presented with dyspnoea and cyanosis one hour after birth.
Which of the following features would be expected?
(Please select 1 option)
Both apex beat and trachea are likely to be deviated to the left
The abdomen would also be distended
The first resuscitative measure would be to supply oxygen and assist ventilation with a face mask
The most common site of the diaphragmatic defect is on the right
The prognosis would be better for a baby that presented later at 48 hours after birth

The prognosis would be better for a baby that presented later at 48 hours after birth This is the correct answerThis is the correct answer
The displacement of abdominal contents into the thoracic cavity occurs. The stomach and abdominal contents cause displacement of thoracic structures to the right, and lung collapse ensues.

A diaphragmatic hernia is a surgical emergency. The abdominal organs must be replaced into the abdominal cavity, and the opening in the diaphragm repaired. Children presenting late tend to have smaller hernias with less respiratory compromise.

Invasive ventilation is necessary immediately after birth until the infant recovers from surgery. Some infants are placed on ECMO (extracorporeal membrane oxygenation), a heart/lung bypass machine which enables the lungs to expand after surgery.

43

In a trial of a new therapeutic agent, the required sample size varies with which of the following?
(Please select 1 option)
Experience of the investigator
Level of acceptance of failing to discover a true effect
Level of statistical significance required
Type of patient recruited
Type of statistical test to be employed

Level of statistical significance required

Sample size influences level of significance through its use in the calculation of SD/SE.

It does not affect

The level of acceptance
The alternative hypothesis with a general level set at p

44

A 45-year-old male presents with severe abdominal pain and vomiting with radiation through to his back. He has a past history of hypertension and excess alcohol consumption.

Amylase
The 45-year-old male has a history suggestive of pancreatitis and an amylase would provide the diagnostic information. None of the others would provide this.

45

A 43-year-old female presents with a peri-anal abscess. She is noted to have a body mass index of 35.6 kg/m2 and has a history of recurrent intertrigo.

Glucose
The 43-year-old female has a perianal abscess, is obese and has a long history of intertrigo. This should prompt investigation for diabetes and preferably a fasting glucose should be measured.

46

A 72-year-old male presents one day following a TURP with a fit. On examination he is drowsy with up going plantar responses.

Urea and electrolytes
The elderly male with fits following TURP suggests a diagnosis of acute hyponatraemia and U+Es need to be measured. Acute hyponatraemic encephalopathy is a life threatening condition with features developing due to cerebral oedema. Some patients may be prone to this postoperatively due to the release of ADH precipitated by pain and anaesthetic agents, creating SIADH. A complication of TURP may be transurethral resection syndrome which is not associated with SIADH secretion.

47

A 47-year-old female presents one week after a partial thyroidectomy performed for a multinodular goitre with tiredness and paraesthesia of her hands.

Calcium
The 47-year-old female has symptoms suggestive of acute hypocalcaemia with hand paraesthia following thyroidectomy. Symptomatic hypocalcaemia may occur in up to 25% of thyroidectomies.

48

A 72-year-old male presents with increasing deformity of his left tibia which he has noticed over the last one year. Examination reveals a bowing of the left tibia.

Alkaline phosphatase
The 72-year-old male with a bowed tibia is likely to have Paget's disease and the most appropriate investigation would be measurement of alkaline phosphatase. The concentration is usually markedly elevated. x Rays are also usually diagnostic.

49

A 19-year-old female is admitted with abdominal pain and vomiting. She has a one month history of weight loss and thirst. Examination reveals that she is dehydrated and has a BMI of 19 kg/m2.

Glucose
In this young girl's case the one month history of thirst and weight loss is crucial and would be suggestive of diabetes mellitus. The presentation appears to be with diabetic ketoacidosis - abdominal pain and vomiting being a frequent presentation.

In the latest guidance from Joint British Diabetes Societies Inpatient Care Group, arterial blood gas analysis is not recommended over venous blood gases. The difference between the two "will change neither diagnosis nor management of DKA and it is not necessary to use arterial blood to measure acid base status" 1 (p 8). Furthermore, the guidance states that "arterial line insertion should only be performed if its use will influence management i.e. for frequent arterial oxygen level measurements or monitoring blood pressure in the critically unwell patient"1 (p 8).

50

Masking individuals and investigators in the trial from the treatment assignment.

Double blinding
Double blind refers to a type of research study. In a double blind study, neither the study participants nor the person giving the treatment know which treatment any particular subject is receiving. In this way, both the researchers and the study participants are 'blind' to who is receiving which treatment during the study.

This method helps researchers get more accurate results from their research. Double blinding allows researchers to 'control' a study for the psychological effects that sometimes help people feel better, simply because they expect to feel better when they receive a medication. In other words, double blinding helps researchers separate the 'power of suggestion' from the real effects of a medication or therapy.

51

A measure of how much an intervention impacts upon a specified outcome compared with that of the non-interventional group.

Relative risk
Relative risk is a measure of how much a particular risk factor (say cigarette smoking) influences the risk of a specified outcome such as lung cancer, relative to the risk in the population as a whole.

52

An outcome usually, but not necessarily, beneficial, that is attributable to an expectation of an effect.

Placebo effect
A beneficial effect in a patient following a particular treatment that arises from the patient's expectations concerning the treatment rather than from the treatment itself is termed the placebo effect. Studies reveal that this effect can be potent.

53

Occurs when subjects that are chosen are not representative of the target population.

Selection bias
Selection bias is an error in choosing the individuals or groups to take part in a study. Ideally, the subjects in a study should be very similar to one another and to the larger population from which they are drawn (for example, all individuals with the same disease or condition). If there are important differences, the results of the study may not be valid.

54

Gives an estimated range of values which is likely to include an unknown population parameter, the estimated range being calculated from a given set of sample data.

Confidence interval
A confidence interval is a statistical range with a specified probability that a given parameter lies within the range.

55

Carcinoma of the prostate

PSA
Tumour markers are commonly used to identify cancers, or are used as a screening test for certain cancers. An example of this is PSA for prostate cancer in men.

56

Hepatocellular carcinoma

Alpha-fetoprotein
Alpha-fetoprotein is often elevated in patients with hepatocellular carcinoma. It is also found in non-seminomatous germ cell tumours of the gonads. Beta-HCG is a tumour marker that may be found in bronchial carcinoma. It is also found in choriocarcinomas.

57

Ovarian carcinoma

CA-125
Ca-125 is typically elevated in association with ovarian malignancy.

58

A 77-year-old woman is admitted as an emergency with dehydration following an episode of gastroenteritis.
Past medical history includes an ileostomy for Crohn's disease 30 years previously and hypertension. She is noted to be hypokalaemic at 2.9 mmol/L (3.5-5.5).
Which of the following is a reasonable explanation for her potassium level?
(Please select 1 option)
Blood transfusion
Chronic renal failure
Use of amiloride
Use of furosemide
Use of spironolactone

Use of furosemide

Furosemide is a loop diuretic and would lead to hypokalaemia.

The other options are all common causes of hyperkalaemia.

Many patients are inadequately resuscitated both as emergency admissions and post-operatively and it is important to identify and treat causes of salt loss, for example, anti-emetics/anti-diarrhoeal agents as well as correcting the potassium imbalance.

59

A 62-year-old woman develops a pancreatic fistula following a Whipple resection for adenocarcinoma.
What is her uncorrected acid base status likely to be?
(Please select 1 option)
Metabolic acidosis
Metabolic alkalosis
Normal
Respiratory acidosis
Respiratory alkalosis

Metabolic acidosis

In the presence of an untreated pancreatic fistula there will be a large loss of bicarbonate leading to a fall in pH.

Respiratory compensation will include blowing off the carbon dioxide to reduce the acidosis and the kidneys will try to secrete hydrogen and hold onto bicarbonate.

The use of somatostatin analogues slows down the pancreatic losses and so reduces the loss of bicarbonate.

60

A 28-year-old man is recovering following a laparotomy for perforated appendicitis 24 hours previously.
His pain scores are constantly 9-10 and the pain team review is awaited.
If his blood gases were checked what would be the likely finding?
(Please select 1 option)
Metabolic acidosis
Metabolic alkalosis
Normal
Respiratory acidosis
Respiratory alkalosis

Respiratory acidosis

Patients in pain after surgery especially those undergoing major abdominal operations will show evidence of a respiratory acidosis as a result of hypoventilation not clearing the carbon dioxide.

Patients should be provided with adequate analgesia for their pain so as to prevent this complication but care should be taken not to cause central nervous system suppression as this would exacerbate the situation.

61

Exudative ascites occurs in which of the following?
(Please select 1 option)
Congestive cardiac failure
Constrictive pericarditis
Hepatic failure
Nephrotic syndrome
Peritoneal malignancy

Peritoneal malignancy This is the correct answerThis is the correct answer
A transudate has a low protein concentration (25 g/l).

Tuberculous peritonitis
Peritoneal malignancy
Budd-Chiari syndrome
Pancreatic ascites
Chylous ascites and
Meigs syndrome
are all due to an exudate.

62

The stroke mortality rates of areas X and Y are the same.
The SMR (Standardised Mortality Ratio) for stroke in X is 110 and the SMR for stroke in Y is 90.
Which one of the following can be deduced?
(Please select 1 option)
Incidence of stroke is higher in X than in Y
The age-specific mortality rates for stroke are lower in X than in Y
The case fatality for stroke is higher in X than in Y
The numbers of deaths coded as due to stroke are the same in the two areas
The population in area X is, on average, younger than in Y

The population in area X is, on average, younger than in Y This is the correct answerThis is the correct answer
This epidemiological study finds the stroke mortality the same for both areas but this is not the entire picture as, if the stroke mortality rates are the same (say 4%) for the population yet the SMR for X is 20 points higher than that of Y then the population of X is younger (strokes occurring at a younger age group hence higher SMR).

The incidence is the number of strokes occurring in the population which is the same for both areas.

The case fatality rate is calculated as the number that have the condition who die from that condition. This cannot be determined from the figures provided, as for whatever reason the mortality rate could be lower (or higher) in X despite the mortality rates being the same.

63

Which of the following is not observed in Crohn's disease?
(Please select 1 option)
Dermatitis herpetiformis
Erythema nodosum
Haemolytic anaemia following sulphasalazine treatment
Pyoderma gangrenosum
Steatorrhoea

Dermatitis herpetiformis is a manifestation of coeliac disease.

Fat malabsorption may be a feature of crohn's with Erythema nodosum and pyoderma gangrenosum being cutaneous manifestations.

Oligoarthritis with Sacroilitis and iritis may also feature.

Sulphasalazine can produce a number of haematological problems in particular thrombocytopaenia, leucopaenia but haemolysis can occur.