Screening II Flashcards
Define detection rate (DR).
The proportion of affected individuals with a positive test result
Define false positive rate (FPR).
The proportion of unaffected individuals with a positive test result
Define the odds of being affected given a positive test result (OAPR).
True positives : False-positives
Which of the following depend on the prevalence of the disorder being screened for?
DR, FPR, OAPR
OAPR
What is the risk of a 30 year old woman with a serum AFP value of 0.4 MoM having a pregnancy with Down syndrome?
LR x prevalence = 3 x 1:1000
= 3:1000
Prevalence of Down syndrome with a maternal age of 30?
1:1000
Prevalence of Down syndrome with a maternal age of 40?
1:100
Simply, how do you calculate test specific risk?
LR x age specific risk
How do you calculated a combined LR?
X the two together (if the tests are independent)
What is the quadruple test?
Distribution of risk of Down’s syndrome in
affected and unaffected pregnancies using AFP, uE3, total hCG and inhibin-A at 14-20 weeks with maternal age
What is medical screening?
The systematic application of a test or inquiry, to identify
individuals at sufficient risk of a specific disorder to
benefit from further investigation or direct preventive
action, among persons who have not sought medical
attention on account of symptoms of that disorder.
Understand why cholesterol and blood pressure measurement are poor screening tests for cardiovascular disease.
The distributions for died of IHD and died of IHD for both cholesterol and BP overlap almost completely so it isn’t a good measurement. The detection rate is only about 15% and the false positive rate is 5%.
The same can be said for stroke.
What are better screening tests for cardiovascular disease?
History of cardiovascular disease - 50% of IHDs occur in pts who had a previous MI or stroke
Diabetes - relative risk 2-6
Age - 96% of IHD deaths are in over 55s
What is the screening test for future AAA?
Measure max. aortic diameter
AAA >6cm in diameter - what is the mortality rate with/without surgery?
With 5%, without 50%