Session 7

Question 1

How can disease be detected?

Answer 1

Spontaneous presentation
Opportunistic case finding
Screening

Question 2

What is Spontaneous presentation?

Answer 2

The person presents with symptoms and defines self as patient eg. GP, A&E

Question 3

What is Opportunistic case finding?

Answer 3

Person presents with symptoms relating to a disease/problem

Gp takes the opportunity to check for other diseases eg Urine dipstick, Blood pressure

Question 4

What is Screening?

Answer 4

Systematic attempt to detect an unrecognised condition (So no signs/symptoms yet) by the application of tests, examinations or other procedures
Can be applied rapidly and cheaply to distinguish between apparently well people who probably have a disease (or its precursor) an those who probably do not

Question 5

What happens if a patient screens positive for a disease?

Answer 5

They are at a high risk of getting the disease and will have diagnostic tests to see if they have the disease or not
Does NOT mean they definitely have the disease

Question 6

How many patients with a positive screen for breast cancer have it?

Answer 6

~8%

Question 7

What is the purpose of screening?

Answer 7

To have a better outcome compared to if the patient had found it in the usual way
Finding something earlier is NOT the primary outcome of screening
There is no point in screening if treatment can wait until symptoms appear with no difference in survival rates

Question 8

What are some examples of the NHS screening programmes in the UK?

Answer 8

Breast cancer
Bowel cancer
Cervical cancer
Diabetic retinopathy (Specific population)
Abdominal Aortic aneurysm (Men at a specific age)
Fetal abnormalities

Question 9

What features should the disease have for a screening process?

Answer 9

Must be an important health problem
Epidemiology and Natural history must be understood
Must have an early detectable stage
Cost effective Primary prevention interventions must have been considered and implemented where possible

Question 10

What properties should all Screening tests have?

Answer 10

Simple & safe (As will be screening healthy people)
Precise & valid
Acceptable to the population
Distribution of test values in the population must be known
Agreed cut off level must be defined
Agreed policy on who to investigate further

Question 11

What are the 2 main errors any screening test will make?

Answer 11

False positives (Healthy people who test positive)
False negatives (Ill people who test negative)

Question 12

What are the features of test validity?

Answer 12

Sensitivity (Detection rate)
Specificity
Positive predictive value
Negative predictive value

Question 13

What is Sensitivity of a test?

Answer 13

Proportion of people with the disease who test positive

Question 14

How do you calculate sensitivity?

Answer 14

True positives / (True positives + False negatives)

Question 15

What does high sensitivity mean?

Answer 15

The test is good at correctly identifying people with the disease you are screening for

Question 16

What is Specificity of a test?

Answer 16

Proportion of people without the disease who test negative

Question 17

How do you calculate specificity?

Answer 17

True negatives / (False positives + True negatives)

Question 18

What does a high specificity mean?

Answer 18

Test is good at identifying people without the disease as not having the disease

Question 19

Sensitivity & Specificity are a function of the characteristics of the test, what does this mean?

Answer 19

That when the test is applied in the same way in different populations, the test will have the same Sensitivity and Specificty

Question 20

What is the Positive predictive value?

Answer 20

Proportion of people who test positive that actually have the disease
Value is strongly influenced by the prevalence of the disease (A low prevalence disease may have a lower PPV than a higher prevalence disease even if the sensitivity and specificity of the tests are the same)

Question 21

How do you calculate the Positive predictive value?

Answer 21

True positives / (True positives + False positives)

Question 22

How do you calculate the prevalence of a disease?

Answer 22

(True positives + False negatives) / Whole population

Question 23

What is Negative predictive value?

Answer 23

Proportion of people who are test negative who actually do NOT have the disease

Question 24

How do you calculate Negative predictive value?

Answer 24

True negatives / (False negatives + True negatives)

Question 25

What are the implications of a False positive result?

Answer 25

The test indicates patient may have the disease when they do not.
Patients will have to undergo invasive tests
May lead to lower uptake of screening programmes
Uneccessary stress

Question 26

What are the implications of a False negative result?

Answer 26

The test indicates patient doesn’t have the disease when they do
Will not be offered diagnostic test
False reassurance so may present with symptoms later

Question 27

For a screening programme to be approved, what sort of treatment should be available?

Answer 27

Effective evidence based
Early treatment that is advantageous
Agreed policy on who to treat

Question 28

What should a screening programme have to be approved?

Answer 28

Facilities for counselling
Facilities for diagnosis & treatment
Quality assurance for the whole programme
Proven effectiveness
Benefit should outweigh physical/psychological damage

Question 29

What type of Health intervention is Screening an example of?

Answer 29

Secondary

Question 30

What is the Lead time bias?

Answer 30

Patients live the same length of time (Whether they were screened or not) but they live longer knowing they have the disease

Question 31

What is a bias associated with screening?

Answer 31

Those who have regular screening are likely to do other things to protect their health

Question 32

What are the sociological critiques of screening?

Answer 32

Victim blaming (Individuals encouraged to take responsibility for own health, not all may be equally able to do this)
Individualising pathology