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Flashcards in Secondary Prevention Deck (26)
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1
Q

Define screening.

A

A process of identifying apparently healthy people who may be at increased risk of a disease.

2
Q

List 3 things that screening leads to early detection of.

A

1 - Disease.

2 - Precursors to disease.

3 - Susceptibility to disease.

3
Q

List 4 ways by which screening can be done.

A

1 - Questionnaires.

2 - Examinations.

3 - Lab tests.

4 - Imaging.

4
Q

Define sensitivity (with regards to test characteristics).

A
  • The proportion of all tests for those that have a disease that are true positives.
  • How good the test is at picking up disease.
5
Q

What is the effect of a highly sensitive test on false negatives?

A

The number of false negatives are decreased.

6
Q

Is a highly sensitive test more useful when the result is positive or negative?

A

Negative.

7
Q

Define specificity (with regards to test characteristics).

A
  • The proportion of all tests for those that do not have a disease that are true negatives.
  • How good the test is at correctly excluding people without the condition.
8
Q

What is the effect of a highly specific test on false positives?

A

The number of false positives are decreased.

9
Q

Is a highly specific screening test more useful if the result is positive or negative?

A

Positive.

10
Q

What is the positive predictive value?

A
  • The proportion of all positive tests that are true positives rather than false positives.
  • If you test positive, how likely is it that you really do have the disease?
11
Q

What is the negative predictive value?

A
  • The proportion of all negative tests that are true negatives rather than false negatives.
  • If you test negative, how likely is it that you really don’t have the disease?
12
Q

How can a set of test results be used to calculate the prevalence of a disease?

A

Prevalence = true positives + false negatives / all results

13
Q

In which populations might the rate of false positives be high?

A

In very low risk populations.

*To test this, create a table with disease + and - against test + and - and use a specificity and sensitivity of 99%.

14
Q

How does prevalence affect the positive predictive value and the negative predictive value?

A
  • At low prevalences, the negative predictive value is high and the positive predictive value is low.
  • At high prevalences, the positive predictive value is high and the negative predictive value is low.
  • Where the prevalence is 50%, both values are high.
15
Q

What is the national screening committee (NSC)?

A

A group that advises the NHS in the 4 UK countries about population screening.

16
Q

List 4 examples of NSC-approved screening programmes in the UK.

A

Antenatal and newborn:

1 - Fetal anomaly screening programme (FASP).

2 - Infectious diseases in pregnancy screening programme (IDPS).

Young person and adult:

1 - Abdominal aortic aneurysm programme (AAA).

2 - Bowel cancer screening programme (BCSP).

17
Q

List 2 examples of non-NSC-approved screening programmes in England.

A

1 - Prostate cancer risk management.

2 - National chlamydia screening programme.

18
Q

List 3 things that are needed to make the screening process possible.

A

1 - A disease with a pre-clinical detectable period (time between onset of disease and first symptoms).

2 - A test that can be applied.

3 - Treatment that will alter the outcome of the disease.

19
Q

List the 4 criteria that are assessed by the NSC when appraising the viability and effectiveness of a screening programme.

A

1 - The condition.

2 - The test.

3 - The intervention

4 - Implementation.

20
Q

List the biases that arise when comparing outcomes in patients identified by screening to those identified clinically.

A

1 - Volunteer bias.

2 - Lead time bias.

3 - Length bias.

21
Q

Define volunteer bias.

A

The bias that arises from the difference in health between populations that choose to attend screening and populations that do not.

22
Q

Define lead time bias.

A
  • The bias that arises from the difference in time by which a diagnosis occurs because of screening as opposed to being diagnosed in a usual clinical setting.
  • E.g. screening can have an impact on the amount of time between diagnosis and death, but no impact on when death actually occurs.
23
Q

Define length time bias.

A

The bias that arises from the increased probability of screening to detect individuals with a long pre-detectable period.

24
Q

Define pre-clinical detectable period.

A

The time between onset of disease and first symptoms.

25
Q

Describe the case of mammography screening in 40-49 year olds in the USA in 1996.

A
  • The national institute of health concluded that there was insufficient data to warrant screening.
  • There was a national response saying that the report was fraudulent.
  • The head of the NIH asked the committee to reconsider, and a revised recommendation was made in favour of screening every 1-2 years.
26
Q

Describe the case of the 2001 BMJ article ‘European women’s group calls for HPV testing’.

A
  • The article stated that many high profile women were pressing for HPV screening, and that the evidence for HPV screening was overwhelming.
  • In reality, the evidence suggested no benefits, and that there was possibly more harm from over-detection, costs and stigma.
  • An investigation found that none of the celebrities were involved, and that the campaign was run by a PR firm working for the manufacturers of the HPV test.