Secondary Prevention Flashcards
Define screening.
A process of identifying apparently healthy people who may be at increased risk of a disease.
List 3 things that screening leads to early detection of.
1 - Disease.
2 - Precursors to disease.
3 - Susceptibility to disease.
List 4 ways by which screening can be done.
1 - Questionnaires.
2 - Examinations.
3 - Lab tests.
4 - Imaging.
Define sensitivity (with regards to test characteristics).
- The proportion of all tests for those that have a disease that are true positives.
- How good the test is at picking up disease.
What is the effect of a highly sensitive test on false negatives?
The number of false negatives are decreased.
Is a highly sensitive test more useful when the result is positive or negative?
Negative.
Define specificity (with regards to test characteristics).
- 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.
What is the effect of a highly specific test on false positives?
The number of false positives are decreased.
Is a highly specific screening test more useful if the result is positive or negative?
Positive.
What is the positive predictive value?
- 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?
What is the negative predictive value?
- 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?
How can a set of test results be used to calculate the prevalence of a disease?
Prevalence = true positives + false negatives / all results
In which populations might the rate of false positives be high?
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%.
How does prevalence affect the positive predictive value and the negative predictive value?
- 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.
What is the national screening committee (NSC)?
A group that advises the NHS in the 4 UK countries about population screening.
List 4 examples of NSC-approved screening programmes in the UK.
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).
List 2 examples of non-NSC-approved screening programmes in England.
1 - Prostate cancer risk management.
2 - National chlamydia screening programme.
List 3 things that are needed to make the screening process possible.
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.
List the 4 criteria that are assessed by the NSC when appraising the viability and effectiveness of a screening programme.
1 - The condition.
2 - The test.
3 - The intervention
4 - Implementation.
List the biases that arise when comparing outcomes in patients identified by screening to those identified clinically.
1 - Volunteer bias.
2 - Lead time bias.
3 - Length bias.
Define volunteer bias.
The bias that arises from the difference in health between populations that choose to attend screening and populations that do not.
Define lead time bias.
- 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.
Define length time bias.
The bias that arises from the increased probability of screening to detect individuals with a long pre-detectable period.
Define pre-clinical detectable period.
The time between onset of disease and first symptoms.
Describe the case of mammography screening in 40-49 year olds in the USA in 1996.
- 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.
Describe the case of the 2001 BMJ article ‘European women’s group calls for HPV testing’.
- 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.
