Prevention and screening

Question 1

What criteria used for screening?

Answer 1

Wilson and Jungner criteria

Question 2

Types of prevention and example of each?

Answer 2

Primary - Prevent onset of disease (exercise more, eat well)
Secondary - Early identification of disease and prevent disease from worsening (QRisk and statin administration)
Tertiary - Rehab following significant illness (medication post-MI +/- PCI)

Question 3

What is the definition of screening?

Answer 3

A process which sorts out apparently well people who probably have a disease from those who probably do not.

Question 4

Types of screening?

Answer 4

Population-based screening programmes
Opportunistic screening
Screening for communicable diseases
Pre-employment and occupational medicals
Commercially provided screening

Question 5

What are some of the Wilson and jungner criteria?

Answer 5

The condition:
Important health problem
Latent / preclinical phase
Natural history known

The screening test:
Suitable
Acceptable

The treatment:
Effective
Agreed policy on who to treat

The organisation and costs:
Facilities
Costs and benefits
Ongoing process

Question 6

Define sensitivity

Answer 6

the proportion of people with the disease who are
correctly identified by the screening test

Sensitivity = No. of true positives/(no. of true positives + false negatives)

High sensitivity ideal for contact tracing purposes in a pandemic

Question 7

Define specificity

Answer 7

the proportion of people without the disease who are
correctly excluded by the screening test

Specificity= No. of true negatives/(no. of true negatives+ false positives)

Question 8

Define positive predictive value

Answer 8

the proportion of people with a positive test

result who actually have the disease

Question 9

Define negative predictive value

Answer 9

the proportion of people with a negative

test result who do not have the disease

Question 10

Difference between predictive values and sensitivity/specificity?

Answer 10

Predictive values based on underlying prevalence. Sensitivity and specificity are not.

Question 11

Type of bias in screening?

Answer 11

Lead-time bias (Screened patients have same survival rate as those not screened)
Length-time bias (less aggressive cancers more likely to be picked up from screening compared to more aggressive cancers –> hence die later)