An Initiative of the EMRA Research Committee
Terms
Positive Predictive Value (PPV): The probability that a positive test result predicts disease
Negative Predictive Value (NPV): The probability that a negative test result predicts no disease
| Disease | No Disease | |
| Test + | A | B |
| Test - | C | D |
PPV= A/(A+B) NPV= D/(D+C)
Example: Transvaginal ultrasound (TVUS) has a 94% PPV and 100% NPV in the diagnosis of ectopic pregnancy.
What does this mean?
PPV: If a patient has a positive TVUS, there is a 94% probability that they have an ectopic pregnancy.
NPV: If a patient has a negative TVUS, there is a 100% probability that they do NOT have an ectopic pregnancy.
Extra Point: As the prevalence of a disease increases, the PPV increases. As the prevalence of a disease decreases, the NPV increases.