Screening

Question 1

Define “screening”

Answer 1

The systematic application of a test to identify individuals at sufficient of a disorder to warrant further investigation or prevention amongst people who have sought medical attention on the account of symptoms

Question 2

Give three examples of screening tests

Answer 2

1. Ultrasound to identify a wide abdominal aorta
2. Measuring serum AFP, bhCG, oestriol during pregnancy for Down’s syndrme
3. Guthrie test for PKU

Question 3

Why should we screen?

Answer 3

• Opportunities for primary prevention are limited
• Opportunities for treatment are limited
• Screening gives potential for early or more effective treatment

Question 4

For a condition to be appropriately screened, what kind of symptom profile should it have?

Answer 4

Diseases must have a pre-symptomatic phase for it to be detected by a screening programme

Question 5

What is it about a condition which makes it an appropriate candidate for a screening test?

Answer 5

1. It must be an important health problem
2. The epidemiology / history of condition must be understood, should be a detectable risk factor and a pre-symptomatic period
3. Cost-effective primary prevention should already have been implemented

Question 6

What does a screening test have to be for it to be a candidate for a screening test?

Answer 6

1. It should be simple, safe, precise and validated
2. Test values should be known with an agreed cut off
3. Test should be acceptable to patients

Question 7

What things should we bear in mind when considering the treatment following a screening programme?

Answer 7

1. There should already be an effective treatment in place with better outcomes
2. Agreed policies who should be offered treatment
3. Management of condition should be optimised before a screening programme

Question 8

What things should we bear in mind when setting up the logistics of a screening programme itself?

Answer 8

1. Must have RCT evidence that programme is effective in reducing mortality / morbidity
2. Evidence it is acceptable to professionals and public
3. Benefit of programme > harm of it
4. Opportunity cost should be balanced to healthcare spending
5. Plan for quality assurance / adequate staffing / facilities

Question 9

Define “selection bias”

Answer 9

Selection of individuals in such a way that proper randomization is not achieved, thereby ensuring that the sample obtained is not representative of the population

Question 10

Define “length bias”

Answer 10

The idea that screening detects more slowly progressing diseases and diseases with short pre-symptomatic stages are harder to pick up

Question 11

Define “lead time bias”

Answer 11

The length of time between detection of disease and its usual clinical presentation

Question 12

Define “overdiagnosis”

Answer 12

Diagnoses of conditions which are either non-growing / slow-growing that would not cause problems or shorten your life