School of Nursing and Academic Division of Midwifery

RLO: Positive and Negative Predictive Value of Diagnostic Tests

Introduction
Tests
False results
Prediction table
Using PPV and NPV
Assessment
Feedback
Resources

Using PPV and NPV

What does a Positive Predictive Value of 85% mean? For every 100 positive tests in patients from a similar population how many would be true positives?

A positive test result usually means that a patient will have treatment or a further test.

In an asthma clinic a positive test is followed by corticosteroid treatment. If there are 20 positive tests and a PPV of 75%, how many patients would be given corticosteroids unnecessarily?

The NPV for the same test in the same clinic is 90%. For every 20 patients who test negative, how many will be false negative?

DISCLAIMER: The clinical examples in this RLO are there purely to provide context. They should not be used to guide or inform patient care.

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