Exercise: Test for urinary tract infection, answer 3

Question 3: The positive predictive value of urine Gram stain was 94.3%. What does this mean and what can we conclude?

Suggested answer:

The positive predictive value of a test is the proportion of those people who are positive on the test who actually have the disease, i.e. have a urinary tract infection. It depends not only on the test but on the population in which the test is being used.

94.3% is very high, so, among those whose urine is sent for urine culture, most people who are detected by the urine Gram stain test will actually have a UTI.

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