Screening II

Question 1

Define detection rate (DR).

Answer 1

The proportion of affected individuals with a positive test result

Question 2

Define false positive rate (FPR).

Answer 2

The proportion of unaffected individuals with a positive test result

Question 3

Define the odds of being affected given a positive test result (OAPR).

Answer 3

True positives : False-positives

Question 4

Which of the following depend on the prevalence of the disorder being screened for?
DR, FPR, OAPR

Answer 4

OAPR

Question 5

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?

Answer 5

LR x prevalence = 3 x 1:1000

= 3:1000

Question 6

Prevalence of Down syndrome with a maternal age of 30?

Answer 6

1:1000

Question 7

Prevalence of Down syndrome with a maternal age of 40?

Answer 7

1:100

Question 8

Simply, how do you calculate test specific risk?

Answer 8

LR x age specific risk

Question 9

How do you calculated a combined LR?

Answer 9

X the two together (if the tests are independent)

Question 10

What is the quadruple test?

Answer 10

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

Question 11

What is medical screening?

Answer 11

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.

Question 12

Understand why cholesterol and blood pressure measurement are poor screening tests for cardiovascular disease.

Answer 12

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.

Question 13

What are better screening tests for cardiovascular disease?

Answer 13

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

Question 14

What is the screening test for future AAA?

Answer 14

Measure max. aortic diameter

Question 15

AAA >6cm in diameter - what is the mortality rate with/without surgery?

Answer 15

With 5%, without 50%

Question 16

Who is screened for future ruptured AAA?

Answer 16

Men age 65 and over

- done by ultrasound scan