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FPH exam > 2c screening and diagnosis > Flashcards

2c screening and diagnosis Flashcards

1
Q

What is the aim of screening?

A

To reduce the harm caused by a disease or its complications

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2
Q

define screening

A

Screening is a process of identifying apparently healthy individuals who may be an increased risk of a condition. They can then be offered information, further tests or appropriate treatment to reduce their risk of any complications arising from the disease or condition

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3
Q

who is the organization responsible for approving screening programmes in the UK?

A

The UK national screening commitee

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4
Q

What are the UK national screening committee responsible for

A

Responsible for introducing, modifying or ending screening programmes in the UK based on the best available evidence

Advise the UK chief medical officers on screening policy

Considers the evidence for screening benefits, harms and costs and evaluates these against its own criteria based on Wilson and Jungners WHO criteria for assessing the viability, effectiveness and appropriateness of a screening programme

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5
Q

Give examples of some UK ‘screening’ programmes which are not part of UK NSC national, systematic screening

A
  • PSA (prostate screening)
    -NHS health checks (CVS Screening)
  • national child measuring programme (obesity screening)
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6
Q

UK screening programmes: foetal anomaly screening

A
  • All pregnant women
  • about 12 weeks: downs, edwards, pataus (USS and blood)
  • about 20 weeks: foetal anomaly scan (USS)
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7
Q

UK Screening: Sickle cell and thalassaemia

A
  • All pregnant women
  • fathers if the mother is a genetic carrier
  • not always done through blood test, questionnaire may be used to determine likelihood of being affected
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8
Q

UK screening: Infectious diseases in pregnancy screening programme

A
  • all pregnant women
  • HIV, HepB, syphilis
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9
Q

UK screening: Newborn and infant physical examination

A
  • All newborns
  • with 72 hours of birth and 6-8 weeks
    -looks for:
    1. congenital cardiac disease
    2. cryptorchidism
    3. DDH
    4. congenital cataract
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10
Q

UK screening: newborn hearing screeing

A
  • all newborns in first 4-5 weeks
  • uses automated otoacoustic emission tests
  • if no clear response may need:
    1. retest
    2. use of automated auditory brainstem response
    3. audiology referral
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11
Q

UK screening: cervical screening

A
  • england women aged 25- 64 years
  • 3 yearly until 49 years
  • 5 yearly from 50 years -64 years
  • tests for HPV, if present cells are examined for abnormalities
  • may require:
    1. monitoring
    2. colposcopy
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12
Q

UK screening: diabetic eye disease

A
  • all >12 year olds with diabetes
    -2 yearly if no retinopathy on past 2 screens
  • may need:
    1. monitoring
    2. opthalmology referral
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13
Q

UK screening: AAA screening

A
  • one off men aged 65 years
  • USS
  • may need:
    1. monitoring
    2. vascular referal
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14
Q

UK screening: breast

A
  • women aged50 -71 years
  • mammography 3 yearly
  • may need:
    1. USS, repeat mammogram, fine needle aspiration
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15
Q

UK screening: Bowel

A
  • Faecal immunochemical test (FIT)
  • men and women aged 60-74 years
  • every 2 years
  • may need: colonoscopy
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16
Q

sensitivity

A

The proportion of people who have the disease who test positive

Test specific, not affected by population

a/ a+c

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17
Q

Specificity

A

The proportion of people who do not have the disease who test negative

Test specific, not affected by population

b/b+d

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18
Q

Positive predictive value

A

Proportion of people who test positive who have the disease

a/ a+b

Population specific, affected by population prevalence

Increasing prevalence will result in higher PPV

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19
Q

Negative predictive value

A

The proportion of people who test negative who do not have the disease

d/c+d

Population specific, affected by population prevalence

Increasing population prevalence will result in lower NPV

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20
Q

Constructing a screening table

What goes where?

A

Disease ON TOP
test results ON SIDE

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21
Q

What is threshold setting and what needs to be considered

A
  • Need to decide a cut off point at which a test is ‘abnormal’
  • setting a threshold will be a compromise between sensitivity and specificity. a test sensitive enough to detect all cases will also likely label a few without the disease as abnormal
    -Receiver operating characteristic curves can help in making this decision
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22
Q

what are receiver operating characteristic curves and what are they used for?

A
  • curve that plots sensitivity (true positive rate) on Y axis against 1- specificity on the X axis (false positive rate)
  • for each possible threshold the sensitivity and specificity are calculated and plotted on this curve
  • a straight diagonal line depicts a useless test (ie a true positive is as likely as a false positive- you might as well flip a coin)
  • curves which are up nearer the top left hand corner are better performing
  • ROC curves can be used for:
    1. threshold setting
    2. assessing the accuracy and validity of a test
    3. comparing accuracy and validity of multiple diagnostic tests
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23
Q

What is AUROC and what is it used for

A

-Area under receiver operating characteristic curve
- perfect test (100% sensitive and 100% specifi) would have an AUROC of 1
- an AUROC of 0.5 indicates a useless test- you are as likely to get a true positive as a false positive

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24
Q

What is parallel testing in screening, give an example and what is its impact?

A

When multiple tests are done to look for the condition on the same individual at the same time.

ie quadruple test for downs syndrome antenatally

leads to higher sensitivity but lower specificity

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25
Q

What is serial testing in screening, give an example and what is its impact?

A

When multiple tests are done on the same individual sequentially to screen for a disease

ie cervical screening, samples are tested for HPV first and then under go cytology if positive

Serial testing increases the specificity

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26
Q

In what situations might you want to set a threshold for a higher sensitivity?

A
  • Serious disease with effective treatment
  • risk of infectivity to others
  • subsequent diagnostic tests are cheap and acceptable
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27
Q

In what situations might you want to set a threshold for a higher sensitivity?

A

Subsequent diagnostic tests/ treatment are unpalatable/ expensive

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28
Q

what are screening, diagnosis and case finding and how are they similar/ different

A

SCREENING
Assessing risk of disease in asymptomatic individuals. Used as a guide as to whether or not to offer a diagnostic test

DIAGNOSIS
Offered to people with symptoms, signs or screened positive. Used to determine whether or not the individual has the disease

CASE FINDING
A systematic process of identifying people/ groups at higher risk of a disease or adverse event. Involves systematically searching for people rather than waiting for them to present with active disease

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29
Q

Qualities of a screening test (purpose, threshold, cost, result of the test, invasiveness, population offered the test)

A

PURPOSE
To assess risk of disease in asymptomatic individuals

THRESHOLD
threshold is set to high sensitivity, many of the positive results will be false

COST
test needs to be cheap as many people tested

RESULT OF TEST
result of test indicates ris k of disease to help decide whether to proceed with diagnostic test

INVASIVNESS
often non-invasive

POPULATION OFFERED TEST
asymptomatic individuals at risk of disease where the benefits of offering the test outweigh the risks

30
Q

Qualities of a diagnostic test (purpose, threshold, cost, result of the test, invasiveness, population offered the test)

A

PURPOSE
to determine whether a person has the disease or not

THRESHOLD
threshold is set to high specificty
Diagnostic accuracy is valued above test acceptability

COST
may be higher cost as small number to be tested

RESULT OF TEST
test provides definitive diagnosis

INVASIVENESS
may be invasive

POPULATION OFFERED THE TEST
people with signs, symptoms or screen positive

31
Q

what is case finding and give examples, advantages and disadvantages

A
  • case finding is a process of identifying people or groups who are at higher risk of a disease or adverse event
    -high risk people are systematically searched for rather than waiting for people to present with active disease
  • examples:
    1. GPs identifying patients at high risk of CHD (ie >50 years and high BMI)
    2. identifying cases in communicable disease outbreaks (MOST IMPORTANT)
    3. Identifying people at high risk of unplanned hospital admission (ie using the patients at risk of rehospitalisation (PARR) model)
  • Advantages:
    1. cheap
    2. low personnel demands
    3. allows targeting of resources which may result in a cost saving
    4. can improve the PPV of a test by testing a group with higher prevalence
  • disadvantages
    1. may increase health inequalities as some high risk groups can be hard to access (ie homeless)
32
Q

what is the likelihood ratio?

A

provides an estimate of how many times more likely people with the disease are to have a particular screening result than those without the disease

provides a direct estimate of how much a test result will change the odds of having a disease, and incorporates both the sensitivity and specificity of the test.

There are 2 different likelihood ratios- positive likelihood ratio and negative likelihood ratio

33
Q

what is the positive likelihood ratio and how is it calculated

A

LR+ is the likelihood ratio for a positive result

It indicates by how much the odds of a disease increases if the test is positive

sensitivity/ (1- specificity)

34
Q

what is the negative likelihood ratio and how is it calculated

A

LR- is the likelihood ratio for a negative result

It indicates how much the odds of a disease decrease is the test is negative

(1-sensitivity)/ specificity

35
Q

How to interpret likelihood ratios

A

LR <0.1: indicates test result is associated with absence of disease
LR>1: indicates test result is associated with the presence of disease

36
Q

Why to use post test probability

A

Positive predictive value is sometimes considered a proxy for post test probability.

However, it is often calculated of values for a study population that may have a different disease prevalence and baseline risk factors to the individual you are testing.

It is better to calculate post test probability based on the individuals pre test probability of disease and the likelihood ratio.

37
Q

How might pre test probability be estimated

A

Pre test probability may be estimated in different ways:
1. may simply use population prevalence if nothing is known about individual
2. post test probability (if individual has already had one or more preceding tests)
3. estimation based on clinical characteristics of the individual

38
Q

What is positive post test probability and how is it calculated

A

Calculated using LR+ (sensitivity/1-specificity)

Probability of having the condition if the test is positive

39
Q

What is negative post test probability and how is it calculated

A

Probability of having the condition if the test is negative.

Calculated using LR- (1-sensitivity/specificity)

40
Q

Calculating post test probability stages

A

Pre test odds= pre test probability/ (1- pre test probability)

Post test odds= Pre test odds x likelihood ratio

Post test probability = post test odds/ (1+ post test odds)

41
Q

What is a fagn nomogram

A
  • chart for helping calculate post test probability
  • draw a straight line connecting pre test probability and likelihood ratio and see where it intersects the post test probability this can then be read off.
42
Q

Ethical considerations of screening

A

Using Beauchamp and Childress ethical framework (1979):

JUSTICE
- screening programmes should only be introduced once all primary prevention is in place (as likely to be more cost effective)
- need to ensure screening programmes do not exacerbate health inequalities (need to work to ensure uptake is as good amongst deprived as amongst affluent)

AUTOMONY
- Provide enough information on harms and benefits to enable an informed decision
- communicating risk is notoriously difficult

BENEFICENCE
- all those screened are asymptomatic but at some risk
- screening will have large benefits for few but most will receive no benefit

NON-MALFEASANCE
- Screening can cause harm in many ways which need to be minimised:

  1. psychological trauma from false positives whilst awaiting diagnostic test
  2. increased anxiety from both true and false positives
  3. Overdiagnosis- Treatment of conditions that would not have come to light during a persons lifetime
  4. harm from diagnostic test
  5. Unwarranted reassurance from false negatives
43
Q

Economic considerations of screening

A
  • screening is expensive
  • there is an associated opportunity cost which must be considered
  • there may be some savings from early treatment of people who may not require more expensive treatment for more advanced disease
  • the costs include:
    1. marketing and patient information
    2. Administration
    3. training
    4. staffing
    5. Equipment and machinery
    6. cost of subsequent diagnostic tests
    7. cost of subsequent treatment
44
Q

Legal aspects of screening (5)

A
  • There are some legal considerations when setting up screening:

TEST LISCENCE
The screening test needs regulatory approval

STAFF ACCREDITATION
Diagnosticians involved need appropriate training, qualification and accreditation with a statutory body

CONFIDENTIALITY
Individual level data must be kept confidential and managed in line with Caldicott principals

VULNERABLE GROUPS
The rights of vulnerable groups are protected in law and they should not be coerced into screening, however, the opportunity of screening should be made available to them

CONSENT
Patients should be given adequate information to be able to give informed consent for particpation

45
Q

Social aspects of screening

A

-Attitudes and health beliefs can have a large impact on screening participation
- these attitudes and health beliefs can vary between communities and cultures
- these need to be considered when planning and monitoring screening to ensure a screening programme does not act to widen health inequalities (ie between social classes or ethnic groups)
-need to consider factors likely to increase or decrease screening particpation

46
Q

Social considerations in screening: factors likely to increase screening participation (4)

A
  1. Knowledge of the disease
  2. Perception of susceptibility to disease
  3. perception of disease severity
  4. knowledge of the availability of treatment
47
Q

Social considerations in screening: factors likely to decrease screening participation (9)

A
  1. Perception that disease is rare
  2. Perception that disease is not serious
  3. Fear of diagnosis of the disease
  4. stigmatised condition
  5. Unpalatable screening tests (ie faecal tests)
  6. Socioeconomic barriers (ie cannot read letter, cannot drive to screening site)
  7. Sociodemographic barriers (ie language barrier, cultural barrier (internal exams))
  8. screening site inaccessible
  9. High residential mobility (screening invite letters not received)
48
Q

Mnemonic for GMC requirements for informed choice regarding screening

A

Proud lions fear revealing silly feather umbrellas

49
Q

GMC requirements for informed choice regarding screening

A

Proud lions fear revealing silly feather umbrellas

-PURPOSE of the screening test
-LIKELIHOOD of positive and negative results
-Possibility of FALSE results
- RISKS associated with the screening process
-Any SIGNIFICANT implications of screening for the particular condition (social, medical or financial)
- FOLLOW UP plans

it should always be stressed that as a screening test not a diagnostic test, positive result does not mean definitely has the disease and a negative result does mean definitely does not have the disease.

50
Q

Planning and operational considerations for a screening programme

A

Some planning and operational considerations include:
- Who is eligible for screening
- how will those people be identified (ie GP registers) and contacted
- is there an appropriate screening test
-How often will they be screened
- What will be done with the results
- How will quality assurance be given?

51
Q

What did Wilson and Jungner outline?

A

The WHO criteria for assessing the viability, effectiveness and appropriateness of a screening programme

52
Q

What are the WHO criteria for assessing the viability, effectiveness and appropriateness of a screening programme

A

THE DISEASE
1. important health problem
2. Long latent period
3. Well recognised pre-clinical stage (during which screening could detect)
3. Natural history understood

THE TEST
1. simple and cheap
2. acceptable
3. Valid (Sensitive and specific)
4. reliable

DIAGNOSIS AND TREATMENT
1. Agreed, evidence based, pathway for management of positive results
2. Agreed, evidence based, pathway for treatment when needed
3. Facilities for further diagnosis and treatment available
4. Treatment available that is effective (with early treatment conferring a benefit), safe, acceptable, cost effective.

THE OVERALL SCREENING PROGRAMME
1. RCT evidence that the programme reduces morbidity and mortality
2.Evidence that the screening programme is acceptable
3. Adequate staffing and facilities are available
4. Opportunity cost of screening programme should be economically balanced

53
Q

Evaluating a planned screening service , what are the 4 key components

A
  1. Burden of disease
  2. Feasibility
  3. Effectiveness
  4. cost
54
Q

Evaluating a planned screening service (4 key components): 1. Burden of disease

A

Assessing the disease prevalence and severity and therefore the burden it places on society

55
Q

Evaluating a planned screening service (4 key components): 2. Feasibility

A
  • depends on test availability, ease of delivery, acceptability, availability of treatment and staff and facilities
56
Q

Evaluating a planned screening service (4 key components): 3. effectiveness

A
  • extent to which a screening programme reduces morbidity and mortality
  • this is difficult to assess due to 3 key biases effecting screening programmes:
    1. Selection bias
    2. Lead time bias
    3. Length time bias
  • Overdiagnosis also complicates assessment of effectiveness. The requires long term follow up of large numbers to see what the actual impact on mortality is
57
Q

What are the 3 key biases effecting screening programmes

A
  1. selection bias
  2. lead time bias
  3. length time bias
58
Q

Evaluating a planned screening service (4 key components): 3. effectiveness- what is selection bias

A

selection bias occurs when those people attending screening are systematically different from those who do not

this can work both ways

In some instances more patients at higher risk attend ie if FHx of breast cancer more likely to attend screening

In other instances those at lower risk are more likely to attend (know has health screenee effect) ie more affluent more likely to attend cervical screening but lower risk

Performing a RCT helps eliminate this bias but results may not be generalisable

59
Q

What is the healthy screenee effect

A

When people at lower risk of a disease are the ones more likely to attend for screening

60
Q

Evaluating a planned screening service (4 key components): 3. effectiveness- what is lead time bias

A

People in screened groups can appear to live longer than those in unscreened groups.

However, this may be entirely due to diagnosis being earlier without any difference in actual life expectancy

2 people may have developed cancer at the same time and both lived for 5 years following. If the screened is diagnosed 1 year following developing cancer and the unscreened diagnosed when symptoms develop 3 years after developing cancer the lead time is 2 years. However the early diagnosis had no impact on life expectancy

61
Q

Evaluating a planned screening service (4 key components): 3. effectiveness- what is length time bias

A

Length time bias occurs when cases detected through screening tend to have less aggressive forms of cancer and therefore appear to have a better prognosis than those detetected clinically

This occurs as aggressive cancers which are faster growing are less likely to be detected by screening (as a shorter preclinical phase) and more likely to be detected clinically. These will tend to have a worse prognosis.

The lower risk cancers will be more likely to be detected by screening and have a better prognosis.

This may make it appear that the screening programme improves the prognosis when in truth it is simply because the case mix is systematically different in the groups.

62
Q

Evaluating a planned screening service (4 key components): 4. cost

A

Cost effectiveness of screening compared to other public health interventions should be considered.

Both the costs incurred and the cost savings enabled by screening should be considered.

63
Q

What is a screening pilot study and why is it needed

A
  • before being rolled out nationwide pilot studies are used to compare the theoretical benefits of screening shown in studies (efficacy) with the actual impact in the real world (effectiveness)

This is important as there may be practical issues that were hitherto unapparent ie staff in a service setting may not be as skilled or committed as those in a research setting

64
Q

Give examples of screening programmes which UK NSC are currently consulting on

A

Addition of the Quadruple test the Edwards syndrome screening pathway is currently under consultation

65
Q

Give examples of screening programmes which UK NSC have decided not to implement

A

Decided not to implement the addition of pulse oximetry to newborn physical screening

66
Q

Give examples of screening programmes which are currently under significant research

A

TRANSFORM study- looking at using innovative methods of prostate cancer screening ie MRI

Addition of SMA screening to newborn heelprick screening- currently under research at oxford university

67
Q

Consider examples of when genetics and screening are combined

A
  • Genetic diagnosis can affect screening eligibility ie women with BRCA gene may be eligible for yearly screening MRIs
  • screening is undertaken routinely for genetic conditions such as Trisomy 21
  • genetic testing is done on healthy asymptomatic people who are at risk of a condition (cross between screening and diagnosis)
68
Q

What are the ethical considerations of genetic screening

A

AUTOMONY
- can be compromised if genetic testing is done for adult onset conditions on children before they are able to consent

REPRODUCTIVE CHOICE
- couples with genetic conditions/FHx should receive counselling on their reproductive choices
- this might include antenatal genetic testing +/- termination or pre implantation genetics and IVF
- this is an emotive subject and can raise concern re eugenics
- at its heart any antenatal genetic screening should seek to allow parents reproductive choice rather than reduce prevalence on a genetic condition

IMPACT OF SCREENING
- T21 is routinely screened for
- this is controversial as does it suggest people with T21 are less valuable to society

69
Q

What are the social considerations of genetic screening?

A

Psychological harm can arise due to stigmatisation associated with genetic diagnoses

70
Q

What are the legal considerations of genetic screening?

A

VULNERABLE PEOPLE
- children have a right not to be screened for adult onset conditions until they can consent
- some people may never be able to consent and appropriateness of genetic screening needs careful consideration within a legal framework (ie some with learning difficulties)

CONFIDENTIALITY
- in general usual principles of confidentiality apply however some challenges arise with genetic testing
- Someone elses results can have a significant impact on them ie a pregnant women who would like to know fathers genetic results to inform reproductive choice
- An individual results can effectively provide a diagnosis for someone who would choose not to be tested Ie if a grandmother has Huntington’s, the son has chosen not to be tested but the granddaughter tests positive. The granddaughters diagnosis has effectively diagnosed the father.

USE OF GENETIC INFORMATION
- genetic information may be very useful to certain groups
- the UK currently has moratoria preventing the use of genetic information for underwriting insurance

FPH exam (24 decks)

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