screening

Question 1

define screening

Answer 1

the widespread use of a simple test for a disease in an apparently healthy population.

Question 2

whats a screening programme

Answer 2

an organised system using a screening test among asymptomatic people in the population to identify early cases of a disease in order to improve health outcomes

Question 3

define screening test

Answer 3

a test that is usually cheap and simple, that is used to test large numbers of apparently healthy people to identify individuals suspected of having disease. these people will then go on to have diagnostic test to test the diagnosis

Question 4

what prevention type is screening an example of and why

Answer 4

example of secondary prevention as it aims to limit the consequences of disease through early diagnosis and treatment

Question 5

4 considerations of when we should screen

Answer 5

is the disease appropriate
is the test appropriate
would a screening program be effective
consider benefits vs harms

Question 6

4 considerations when determining if disease is appropriate to screen

Answer 6

seriousness,
ability to alter the course of the disease
lead time
prevalence of pre-clinical disease

Question 7

why consider disease seriousness

Answer 7

screening is resource intensive, so it makes sense to screen for diseases with potentially severe consequences

Question 8

why is prevence of pre-clinical disease an important consideration

Answer 8

screening is resource intensive, its more efficient when there’s a high prevalence of pre-clinical disease.
unless disease is rather serious and the test is easy and cheap

Question 9

why is lead time an important consideration

Answer 9

long lead time means greater chance of detecting disease early

Question 10

what are the three critical points

Answer 10

between first biological onset and disease detectable is critical point one, at this point no disease is detectable.
between DD and symptoms appear is CP 2, screening may be beneficial here
between SA and outcome is CP3 at this point disease is usually diagnosed, so no benefit.

Question 11

what is length time bias

Answer 11

how screening is biased towards detecting slowly developing disease that may not have required treatment, therefore we get the impression of a better prognosis

Question 12

what is lead time bias

Answer 12

when those who are screened earlier for a disease appear to have survived with the disease longer, simply due to an earlier diagnosis date.

Question 13

what are the two intrinsic properties of a test

Answer 13

sensitivity and specificty, there is usually a trade off between these two factors

Question 14

what is sensitivity

Answer 14

proportion of people with the disease who test positive

Question 15

what is specifity

Answer 15

proportion of people without the disease who test negative

Question 16

when do we chose to maximise specificity in a screening test

Answer 16

when there is high cost or high risk involved in the next step

Question 17

when do we choose a screening test which maximises sensitivity

Answer 17

when detecting as many cases as possible is important. costs or risks of the following step is no too high

Question 18

what are predicted values

Answer 18

these are test performance measures in a particular population. these are no intrinsic to the test type

Question 19

whats positive predicted value

Answer 19

the proportion of people who test positive and actually have the disease

Question 20

what is negative predicted value

Answer 20

proportion of people who test negative who don’t have the disease

Question 21

what are PPV and NPV influenced by

Answer 21

these are influenced by the prevalence of the disease in the population, unlike sensitivity and specificity

Question 22

when looking at screening programme effectiveness what do we need to consider
will it be effective?

Answer 22

are there resources to implement and cope with positives,
is the programme actually effective

Question 23

important considerations when looking if there are resources to implement and cope with positives

Answer 23

Facilities and systems
Manage participation
Cost and accessibility
Quality control and monitoring
Treatment
Capacity to treat true positives
Cost effectiveness
Many people over long period
Cost vs benefit

Question 24

what must we consider if we are looking at if the screening test will actually be effective

Answer 24

is there Evidence from Randomized Controlled Trials of benefit (reduced mortality and/or morbidity) prior to initiation
Ongoing evaluation of programmes once implemented

Question 25

what are the benefits of screening programmes

Answer 25

potential for early detection and intervention, reduced mortality or morbidity. there is possible less radical treatment required
there is reassurance for the true negatives
improved health for populations

Question 26

harms of screening tests

Answer 26

all screening programmes are harmful, some do good as well
increases health inequities due to unequal participation or treatment
financial harm to health services
physical harms of the test or receiving diagnostic test when actually a false positive
Psychological- from anxiety from waiting, distress
from invasive tests or procedures, or from false results