Screening

Question 1

What is screening

Answer 1

actively identifying disease/pre-disease in apparently health subjects who may benefit from early treatment

Question 2

What are the criteria for screening to be justified

Answer 2

Condition must be important ie high freq or big impact on individuals

Primary prevention not feasible/effective

There must be an identifiable pre-clinical stage of the disease

There must be a test which separates subjects with a high risk of the disease from subjects with a low risk of the disease

The test must give many true positives/negatives

Question 3

What screening programmes exist in the UK

Answer 3

Bowel cancer screening for 60-74 yr olds every 2 years

Question 4

What biases exist in screening

Answer 4

Lead time bias = wanting screened cases to survive longer

Length bias = slow growing tumours detected by screening

Selection bias + overdiagnosis (may never be diagnosed otherwise)