Exercise: Test for urinary tract infection, answer 4

Question 4: The negative predictive value of urine Gram stain was 95.2%. What does this mean and what can we conclude?

Suggested answer:

The negative predictive value of a test is the proportion of those people who are negative on the test who do not actually have the disease, i.e. have no urinary tract infection. It depends not only on the test but on the population in which the test is being used.

95.2% is very high, so, among those whose urine is sent for urine culture, most people who are negative by the urine Gram stain test will not have a UTI.

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