Screening

Question 1

Define diagnosis

Answer 1

The definitive identification of a suspected disease or defect by application of tests, examinations

To definitely label people as either having a disease or not having a disease

Question 2

Define screening

Answer 2

Process of identifying healthy people who may be at increased risk of disease or condition.

The screening provider then offers info, further tests and treatment. This is to reduce associated risks or complications.

Question 3

What is the purpose of screening?

Answer 3

To give a better outcome compared with finding something in the usual way

Question 4

List the criteria for implementing a screening programme

Answer 4

1) Condition = incidence/prevalence must be understood, primary prevention implemented.
2) Test = simple, safe, precise, validated.
3) Intervention.
4) Screening programme = proven reduced mortality/morbidity, benefit outweighs harm.
5) Implementation = staff, QA

Question 5

List the advantages and disadvantages of screening for disease

Answer 5

A = identify people at risk, catch earlier, provides info, reduce risk and complications

D = will refer well people for further investigation: false +ve, fail to refer people who do actually have an early for of disease: false -ve

Question 6

What are the features of test validity?

Answer 6

1) Sensitivity = proportion of disease who test +ve.
2) Specificity = proportion without disease who test –ve.
3) Positive predictive value = probability that someone who has tested +ve actually has disease.
4) Negative predictive value = proportion of people who test -ve who actually do not have disease

Question 7

How is test sensitivity calculated?

Answer 7

Disease present column = (True +ve) / (true +ve) + (false –ve)

Question 8

How is test specificity calculated?

Answer 8

Disease absent column = (true –ve) / (false +ve) + (true –ve)

Question 9

How is test positive predictive value calculated?

Answer 9

Positive test row = (true +ve) / (true +ve) + (false +ve)

Question 10

How is test negative predictive value calculated?

Answer 10

Negative test column = (true –ve) / (false –ve) + (true –ve)

Question 11

What bias are involved in screening programmes?

Answer 11

Lead time bias = early diagnosis falsely appears to prolong survival (actually just detected earlier, die same time).

Length time bias = better at picking up slow growing unthreatening cases

Selection bias = studies of screening often skewed by ‘healthy volunteer’ effect

Question 12

Give examples of screening programmes in the UK

Answer 12

AAA, 
bowel cancer, 
breast, 
cervical, 
diabetic eye, 
foetal anomaly, 
infectious disease in preg, 
newborn blood spot, 
newborn hearing, 
sickle cell/thalassemia

Question 13

Explain sociological critiques of health promotion and screening

Answer 13

Victim blaming / Individualising pathology.

Individuals and populations increasingly subject to surveillance – prevention as social control?

Moral obligation.

Feminist critiques