Screening

Question 1

What is the purpose of screening?

Answer 1

The purpose of screening is to identify apparently well individuals who have (or at risk of developing) a particular disease so that you can have a real impact on the outcome

Question 2

Disadavantages of screening Important

Answer 2

• Exposure of well individuals to distressing or harmful diagnostic tests
• Detection and treatment of sub-clinical disease that would have never caused any problems
• Preventive intervention that may cause harm to the individual or population

Question 3

Benefits of screening

Answer 3

• Early detection
• Reduced risk of developing a condition or its complications
• Improved QoL
• Informed decisions = screening can help people make better informed decisions about their health
• Reduce mortality
• Reassurance

Question 4

UK screening programmes

Answer 4

3 in pregnancy:
- Infectious diseases in Pregnancy Screening Programme (Hepatitis B, Syphilis, HIV)
- Sickle cell and Thalassaemia Screening
- Foetal Anomoly Screening Programme (DS, Edward’s, Patau)
3 In Newborn Babies:
- Newborn and Infant Physical Examination
- Newborn Hearing Screening Programme (permanent childhood hearing impairment)
- Newborn Blood Spot Screening Programme (sickle cell, CF, Congenital hypothyroidism + 6 inherited metabolic disease)
5 Young People and Adults:
- AAA screening programme
- Bowel Cancer Screening
- Breast Cancer Screening
- Cervical Screening
- Diabetic Eye Screening

Question 5

Wilson and Jungner Criteria Important

Answer 5

• Knowledge of disease
• The Screening Test
• Treatment
• Organisation and Cost

Question 6

How to remember W+J criteria Important

Answer 6

In Exam Season NAP
I = Important Disease
E = Effective Tx available
S = Simple and safe
N = Natural Hx of disease known
A = Acceptable
P = Policy on who to Tx agreed

Question 7

Sensitivity definition Important

Answer 7

Proportion of those with disease who are correctly identified

Question 8

Specificity definition Important

Answer 8

Proportion of people without disease who are correctly excluded by screening test

Question 9

Positive predictive value definition Important

Answer 9

Proportion of people with a positive test result who actually have the disease

Question 10

Negative predictive values definition Important

Answer 10

Proportion of people with a negative test who do not have the isease

Question 11

Calculations Important

Answer 11

Sensitivity = True Positive / (True Positive + False Negatives)
Specificity = True Negative / (True Negative + False Positive)
Positive Predictive Value = True Positive / (True Positive + False Positive)
Negative Predictive Value = True Negative / (True Negative + False Negative)

Question 12

Two types of bias in screening

Answer 12

• Length time bias: occurs when screening is more likely to detect slow-growing disease that has a long phase without symptoms. There will appear to be a survival benefit to screening even when early detection does not improve outcomes
• Lead time bias: occurs when patients diagnosed earlier appear to live longer because they know they have the disease for longer. Awareness of disease may make it falsely seem like early diagnosed patients live longer