Screening

Question 1

This is the widespread use of a simple test for a disease in an apparently healthy (asymptomatic) population)

Answer 1

Screening

Question 2

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

Answer 2

Screening programmes

Question 3

Used to test large numbers of apparently healthy people to identify individuals suspected of having early disease who will then go on to have further diagnostic tests to confirm the diagnosis.

Answer 3

Screening test

Question 4

What is the main difference between a screening test and a diagnostic test?

Answer 4

There is greater emphasis on cost and safety in screening test than in a diagnosis

• screening test: presence of preclinical disease (when people are asymptomatic)
• diagnostic test: measures presence/absence of clinical disease (people become symptomatic)

Question 5

What type of prevention is screening?

Answer 5

Secondary prevention

Question 6

The aim of this is to identify people likely to have pre-clinical disease.

Answer 6

Screening test

Question 7

The aim of this is to establish the presence/absense of a disease

Answer 7

Diagnostic test

Question 8

When should screening tests be performed?

Answer 8

Before the development of clinical disease

Question 9

What is the target population of screening tests?

Answer 9

Asymptomatic individuals who are potentially at very high risk for a disease

Question 10

This aims to improve outcomes and reduce mortality (death due to disease)

Answer 10

Screening

Question 11

This is also known as opportunistic screening.

Answer 11

Case finding

Question 12

What are the 4 points to consider when considering when to screen?

Answer 12

• seriousness of disease
• ability to alter course of disease
• lead time
• prevalence of preclinical disease

Question 13

Why screen just for diseases with potentially severe consequences?

Answer 13

Because screening is resource intensive and it is more efficient when there is a high prevalence of pre-clinical disease.

• there’s no point in screening for the flu

Question 14

This is the period of time when disease is detected through screening to when when a disease is detected/diagnosed symptomatically.

Answer 14

Lead time

Question 15

This is the period of time between the biological onset of disease and the appearance of symptoms.

Answer 15

Pre-clinical disease

Question 16

This is the proportion of people with the disease who test positive.

Answer 16

Sensitivity

Question 17

This is the proportion of people without the disease who test negative.

Answer 17

Specificity

Question 18

What are 2 ways to maximise sensitivity and specificity?

Answer 18

• improving screening test
• choice of disease threshold

Question 19

This measures test performance in a particular population.

Answer 19

Predictive values

Question 20

These 2 measure the intrinsic properties of a test. Measures what proportion of people with or without the disease the test correctly classifies.

Answer 20

Specificity and Sensitivity

Question 21

What influences predictive values?

Answer 21

Prevalence in the population of interest

Question 22

What are 2 things to consider when thinking about the effectiveness of screening programmes?

Answer 22

• resource availability
• evaluating effectiveness (is it actually effective)

Question 23

What are the 3 benefits of screening programmes?

Answer 23

• early detection and intervention (for true positives) (reduced mortality/morbidity and to require less radical treatment)
• reassurance (for true negatives)
• improved health of population

Question 24

This is when screening is biased towards detecting slowly developing disease that may have never required treatment.

Answer 24

Length bias

Question 25

This is a result of when overdiagnosis and/or overtreatment may increase morbidity without reducing mortality. (false positives).

Answer 25

Lead time bias

Question 26

What are some potential harms of screening? (4)

Answer 26

• missed cases of disease (false negatives)
• cost-effectiveness
• over diagnosis and treatment (specifically for false positives)
• decreased health equities (because not everyone will participate equally in the screening programmes)