Screening Flashcards
Give three criteria a disease must meet before being considered for screening
Must be an important health problem
Epidemiology must be well understood
Must have an early detectable stage
Define screening
A systematic attempt to detect an unrecognised condition by the application of tests and examinations, which can be applied cheaply and rapidly to distinguish between apparently well people who probably have a disease and those who probably do not.
Give three criteria a test must meet before being used for screening
Must be simple and safe
Precise and valid
Acceptable to the population
Give three criteria a treatment must meet before being considered in a screening programme
Must be evidence based
Must be advantageous to give treatment early
Their must be an agreed policy on whom to treat
Give three criteria the screening programme must meet to be used in practice
Other options must be available for consideration
Benefits should outweigh both physical and psychological harm
The facilities must be available for treatment
What are false positives?
Well people who are referred for further investigations after screening
What are false negatives?
People who are not referred for follow up post screening despite actually having the disease
Define sensitivity
The proportion of the people with the disease who test positive. Sensitivity = a/(a+c)
Define specificity
The proportion of people without the disease who test negative. Specificity = d/(b+d)
Define ‘positive predictor value’
The probability that someone who has tested positive actually has the disease. PPV = a/(a+b)
Define ‘negative predictor value’
The probability that someone who has tested negative does not actually has the disease. NPV = d/(c+d)
What is ‘lead time bias’
Screened patients appear to survive longer, but only because they were diagnosed earlier - spend a longer time knowing they have a disease.
What is ‘length time bias’
Screening is better at picking up slow-growing diseases then fast- growing ones. There is a possibility a disease picked up screening may never have caused the patient any problems.
Give five examples of screening programmes in the UK
Abdominal aortic aneurysm Bowel cancer Breast cancer Cervical cancer Diabetic retinopathy
What is the ‘surveillance critique’ of screening?
Prevention is purely part of a wider apparatus of surveillance and social control
