Screening Flashcards
What is screening?
Investigating apparently healthy people to detect disease so it can be prevented or delayed
Why do we screen?
- better prognosis e.g. Brest cancer
- identify risk of disease e.g. cholesterol and CVD
- improve outcome and prevent transmission e.g. chlamydia
What are the limitations of screening?
False positives, cause stress and anxiety
What is validity?
The ability for a test to distinguish between those with the disease and those without
What is sensitivity?
The ability for a test to correctly identify those with disease
=CORRECT PEOPLE WITH DISEASE/ALL THE PEOPLE TEST DETECTS HAVE DISEASE
What is specificity?
The ability for a test to correctly identify who doesn’t have the disease
=PEOPLE WHO DON’T HAVE DISEASE AND HAVE BEEN IDENTIFIED/TOTAL WITHOUT DISEASE
What is the positive predicted value?
The likelihood of patient with positive test to have the disease
What is negative predicted value?
Likelihood of person with negative test not having disease
What is the ROC?
Receiver operator characteristic curves are used to determine cut-off value for diagnostic / screening tests
Y axis = sensitivity x axis = 1- specificity
What is the difference between mass and targeted screening?
Mass = whole population Targeted = a certain group
Name some major screening programmes
Antenatal = HIV, Hep B,
Neonatal =sickle cell, phenylketonuria
Cancers = breast, cervical
Infections= chlamydia
3 things to consider about a screening programme
- feasibility = how easy to screen population, facilities
- effectiveness = how does it affect outcomes
- cost
Which 3 biases effect effectiveness of screening
Selection bias
Lead time bias - detect disease that would otherwise be detected later
Length bias = some diseases may not develop to be life threatening but are detected
