Secondary Prevention

Question 1

Define screening.

Answer 1

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

Question 2

List 3 things that screening leads to early detection of.

Answer 2

1 - Disease.

2 - Precursors to disease.

3 - Susceptibility to disease.

Question 3

List 4 ways by which screening can be done.

Answer 3

1 - Questionnaires.

2 - Examinations.

3 - Lab tests.

4 - Imaging.

Question 4

Define sensitivity (with regards to test characteristics).

Answer 4

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

Question 5

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

Answer 5

The number of false negatives are decreased.

Question 6

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

Answer 6

Negative.

Question 7

Define specificity (with regards to test characteristics).

Answer 7

• 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.

Question 8

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

Answer 8

The number of false positives are decreased.

Question 9

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

Answer 9

Positive.

Question 10

What is the positive predictive value?

Answer 10

• 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?

Question 11

What is the negative predictive value?

Answer 11

• 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?

Question 12

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

Answer 12

Prevalence = true positives + false negatives / all results

Question 13

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

Answer 13

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%.

Question 14

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

Answer 14

• 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.

Question 15

What is the national screening committee (NSC)?

Answer 15

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

Question 16

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

Answer 16

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).

Question 17

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

Answer 17

1 - Prostate cancer risk management.

2 - National chlamydia screening programme.

Question 18

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

Answer 18

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.

Question 19

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

Answer 19

1 - The condition.

2 - The test.

3 - The intervention

4 - Implementation.

Question 20

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

Answer 20

1 - Volunteer bias.

2 - Lead time bias.

3 - Length bias.

Question 21

Define volunteer bias.

Answer 21

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

Question 22

Define lead time bias.

Answer 22

• 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.

Question 23

Define length time bias.

Answer 23

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

Question 24

Define pre-clinical detectable period.

Answer 24

The time between onset of disease and first symptoms.

Question 25

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

Answer 25

• 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.

Question 26

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

Answer 26

• 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.