9) Population Based Screening

Question 1

What are the different way in which disease can be detected?

Answer 1

Spontaneous presentation
Opportunistic case finding
Screening

Question 2

What is the purpose of screening?

Answer 2

Give a better outcome compared with finding something in usual way, due to intervening earlier

Question 3

What is screening?

Answer 3

Systematic attempt to detect an unrecognised condition by tests, examination and/or other procedures

Question 4

What is a diagnosis?

Answer 4

Identification of a suspected disease through tests, examination and/or other procedures

Question 5

What are the criteria that need to be considered for a screening programme?

Answer 5

Condition
Test
Intervention 
Programme
Implementation

Question 6

In terms of the condition, what things need to be considered if there is to be a new screening programme?

Answer 6

Important health problem that is well understood

All cost effective primary prevention intervention implemented

Question 7

In terms of the test, what things need to be considered if there is to be a new screening programme?

Answer 7

Simple, safe, precise and validated
Cut off levels defined, test values in pop. known
Acceptable
Agreed policy on further diagnostic investigation to those that test positive

Question 8

In terms of the intervention provided, what things need to be considered if there is to be a new screening programme?

Answer 8

Evidence that intervention at pre-symptomatic phase leads to better outcomes
Agreed policies on which people and what intervention should be offered

Question 9

In terms of the programme itself, what things need to be considered if there is to be a new screening programme?

Answer 9

Effectiveness in reducing mortality
Clinically, socially and ethically acceptable
Benefit gained should outweigh harms

Question 10

In terms of the implementation, what things need to be considered if there is to be a new screening programme?

Answer 10

Patient outcomes optimised
All other options for managing condition considered
Informed choice to potential participants
Quality assurance

Question 11

What is a false positive in screening?

Answer 11

Refer well people for further investigation

Question 12

What are the implications of false positives?

Answer 12

Stress, inconvenience and costs

Lower uptake of screening In future

Question 13

What is a false negative in screening?

Answer 13

Failure to refer those who have an early form of disease

Question 14

What are the implications of false negatives?

Answer 14

Inappropriate reassurance and delayed presentation

Question 15

What is sensitivity?

Answer 15

Detection rate, proportion of people with the disease that test positive (a/a+c)

Question 16

What is specificity?

Answer 16

Proportion of people who don’t have the disease who are correctly identified by the test as not having the disease (d/b+d)

Question 17

What is the positive predictive value?

Answer 17

Probability that someone who is tested positive actually has the disease (a/a+b)

Question 18

What is the negative predictive value?

Answer 18

Proportion of people who are test negative who actually don’t have the disease (d/c+d)

Question 19

Why is evaluation required on screening programmes?

Answer 19

Programmes must be base on good quality evidence

Great pressure to start screening programmes

Question 20

What is lead time bias?

Answer 20

Screened patients appear to survive longer but only because they were diagnosed earlier

Question 21

What is length time bias?

Answer 21

Programmes better at picking up slow growing cases rather than aggressive, fast-growing ones, so screened diseases have favourable prognosis

Question 22

What is selection bias, in reference to screening?

Answer 22

‘Healthy volunteer’ effect - those who are regularly screened likely to do other things that protect them from disease

Question 23

Give some sociological critiques of screening:

Answer 23

Victim blaming
Population increasingly subject to surveillance
Moral obligation
Financial incentives for GPs to put patient in for screening