What Do PPV and NPV Mean? Why Are They Important?
When interpreting NIPT results, it is not enough to only know a "positive" or "negative" result. It is also important to understand how reliable the result is.
What is PPV?
PPV (Positive Predictive Value) is the probability that the baby actually has the condition when the test is positive.
In other words, if the risk is high in the test, it shows how strongly this result actually supports the disease.
What is NPV?
NPV (Negative Predictive Value) is the probability that the baby actually does not have the condition when the test is negative.
In other words, it shows how reassuring the result is in low-risk results.
Why is it Important?
Because even if the sensitivity and specificity of a test are high, the actual meaning of a positive result may not be the same for every patient. Especially PPV can change according to the prevalence of the disease in the population and the risk level of the pregnancy.
Short Summary
- PPV: The probability that a positive result is true
- NPV: The probability that a negative result is true
Important Note
When an NIPT result is high risk, this result usually does not mean a definitive diagnosis. Confirmatory tests such as amniocentesis or CVS may be recommended for diagnosis when necessary.