PASS S8 - Screening

Question 1

What are the 5 areas of criteria?

Answer 1

Condition
Test
Intervention
Screening programme
Implementation

Question 2

What does the condition mean in relation to screening criteria?

Answer 2

An important health problem with epidemiology, incidence, prevalence and natural history understood

Question 3

What does the test mean in relation to screening criteria?

Answer 3

Simple, safe, precise and validated screening test

Distribution of test values in the population must be known and an agreed cut-off level must be defined and agreed

Question 4

What does the intervention mean in relation to screening criteria?

Answer 4

Effective intervention for patients identified through screening, with evidence that intervention at a pre-symptomatic phase leads to a better outcome for the screened individual compared with usual care

Question 5

What does the screening programme mean in relation to screening criteria?

Answer 5

Proven effectiveness in reducing mortality or morbidity

Benefit gained by individuals should outweigh any harms

Question 6

What does implementation mean in relation to screening criteria?

Answer 6

Clinical management and patient outcomes should be optimised in all healthcare providers
All other options for managing the condition should have been considered
Quality assurance of the programme

Question 7

What is lead time bias?

Answer 7

Early diagnosis falsely appears to prolong survival (screened patients appear to survive longer, but only because they were diagnosed earlier)
Patients live the same length of time, but longer knowing they have the disease

Question 8

What is length time bias?

Answer 8

Screening programmes better at picking up slow growing unthreatening cases than aggressive, fast-growing ones
Curing people that don’t need curing

Question 9

What is selection bias?

Answer 9

Studies of screening often skewed by ‘healthy volunteer’ effect
Those who have regular screening likely to also do other things that protect them from disease
An RCT would help deal with this bias

Question 10

Which type of prevention is screening?

Answer 10

Secondary

Question 11

What are the two types of error in screening tests?

Answer 11

False positives

False negatives

Question 12

What is the sensitivity of a test?

Answer 12

The proportion of the people with the disease who test positive
High sensitivity = good at picking up the disease

Question 13

What is the specificity of a test?

Answer 13

The proportion of the people without the disease who test negative
High specificity = good at ruling out people who don’t have the disease

Question 14

What is the positive predictive value?

Answer 14

Probability that someone who has tested positive actually has the disease

Question 15

What is the negative predictive value?

Answer 15

Proportion of people who test negative who actually do not have the disease

Question 16

What factors affect screening uptake?

Answer 16

Acceptability of the test
Awareness of the benefits of screening
Convenience 
Accessibility
Reminders and endorsements

Question 17

Examples of screening programmes

Answer 17

AAA screening
Diabetic eye screening
Breast screening

Question 18

Advantages of screening

Answer 18

Disease diagnosed at an earlier stage = more chance of survival
May give an indication of a disease before any symptoms start showing

Question 19

Disadvantages of screening

Answer 19

Over-diagnosis

Tests aren’t 100% accurate

Question 20

Uptake definition

Answer 20

The proportion of those invited who take up the invitation to participate

Question 21

Coverage definition

Answer 21

The proportion of the eligible population who have been screened within a given time period