S7 - Screening

Question 1

What is screening?

Answer 1

The presumptive identification of unrecognised disease or defect by the application of tests, examinations or other procedures that can be applied rapidly to sort out apparently well persons who probably have the disease from those who probably don’t

Question 2

When are screening test results confirmed with diagnostics tests/procedures?

Answer 2

If the screening test results are high risk.

Low risk results are assumed to be correct until proven otherwise.

Question 3

What is the difference between clinical care and screening?

Answer 3

Clinical care - person goes to health care professional for help with symptoms or concerns.

Screening - health professional goes to person and offers help where there is no symptoms or concerns.

Question 4

What is positive predictive value?

Answer 4

What proportion of people with high risk results are confirmed to have the disease/defect?

The proportion of positive tests who are cases

Question 5

What is a negative predictive value?

Answer 5

What proportion of people with low risk results are confirmed to not have the disease?

The proportion of negative tests who are not cases

Question 6

What are the 5 criteria needing to be satisfied in screening?

Answer 6

1. The condition
2. The test
3. The intervention
4. The screening programme
5. Implementation

Question 7

What needs to be considered about the condition?

Answer 7

The frequency and severity of the condition linked to the understanding of the condition.

Can the carriers be identified?

How cost effective are all the primary interventions?

Question 8

What needs to be considered about the test?

Answer 8

Is it safe, simple and precise?

Question 9

What needs to be considered for the intervention?

Answer 9

Evidence that intervention at pre-symptomatic phase leads to better outcomes?

Question 10

What needs to be considered for the screening programme?

Answer 10

Is there proven effectiveness in reducing mortality or morbidity?

Is the screening programme clinically, socially and ethically acceptable to health professionals and the public?

Does benefit gained outweigh harm?

Question 11

What needs to be considered for the implementation?

Answer 11

Are there management and monitoring programmes?

Have all other options for managing the condition been considered?

Is there adequate staff and facilities available?

Question 12

What is a false positive?

Answer 12

When well people are refered for further investigation

Question 13

What is a false negative?

Answer 13

When it fails to refer people who actually have an early form of the disease

Question 14

What is sensitivity in terms of screening?

Answer 14

The proportion of cases which the test correctly detects

Question 15

What is the specificity in term of screening?

Answer 15

The proportion of non-cases which the test correctly detects

Question 16

SNout

SPin

Answer 16

Sensitive negative - rule them out

Sensitive positive - rule them in

Question 17

How do you work out the sensitivity of a screening result?

Answer 17

(True positive/positive + negative tests of disease present) x 100

Question 18

How do you work out the sensitivity of the screening result?

Answer 18

(True negative/positive + negative results of disease absent) x 100

Question 19

How do you work out the positive predictive value of a screening result?

Answer 19

(True positive/disease present + disease absent in negative test) x 100

Question 20

How do you work out the negative predictive value of a screening result?

Answer 20

(True negative/disease present + disease absent in negative test) x 100

Question 21

What is lead time bias?

Answer 21

Earlier diagnosis falsely appears to prolong survival time

Question 22

What is length time bias?

Answer 22

Screening programmes are better at picking up slowly growing, unthreatening cases than aggressive fast growing ones.

Question 23

What is selection bias?

Answer 23

Studies of screening are often skewed by the healthy volunteer effect - those who have regular screenings are more likely to do other things to protect themselves from disease.

Randomised controlled trials help with this bias.