The performance data for the UNITY Carrier Screen NIPT can be interpreted based on the threshold used for the calculations. The figures below are drawn from the cited validation study of single-gene NIPT (Wynn et al., 2023). Let’s break down what these performance metrics mean:
1. PPV (Positive Predictive Value): PPV indicates the probability that a positive test result accurately reflects the presence of the condition being tested for. The cited validation study reports a PPV of around 50% for the sgNIPT assay in a general-population setting, meaning roughly half of high-chance results reflect a genuinely affected fetus; PPV depends on the specific condition and the mother's carrier status, so a high-chance result should always be confirmed by diagnostic testing.
2. Specificity: Specificity measures the test’s ability to correctly identify individuals who do not have the condition (true negatives). In the cited validation study the specificity of the sgNIPT assay was around 95%, indicating the test is very good at correctly identifying cases where the condition is not present.
3. NPV (Negative Predictive Value): NPV represents the probability that a negative test result accurately reflects the absence of the condition. In the cited validation study the negative predictive value of the sgNIPT assay was around 99.8%. This means that if the test returns a low-chance result, there is a very high probability that the absence of the condition is genuine.
4. Sensitivity: Sensitivity measures the test’s ability to correctly identify individuals who have the condition (true positives). In the cited validation study the sensitivity of the sgNIPT assay was around 96% (about 92% across the end-to-end screening workflow). This suggests that the test is effective at identifying cases where the condition is genuinely present.
In summary, the cited validation data show that UNITY Carrier Screen NIPT demonstrates a moderate PPV, meaning a meaningful proportion of high-chance results reflect a genuinely affected fetus while some do not, so high-chance results should be confirmed diagnostically. The test also exhibits excellent specificity and NPV, meaning that it effectively rules out the condition when it is not present. Additionally, the sensitivity is at a good level, indicating its ability to detect cases with the condition.
It’s important to note that the choice of reporting threshold can impact the performance metrics, and these values are drawn from the cited general-population validation study. Different thresholds may yield different performance outcomes, and healthcare providers often consider the specific clinical context and risk factors when interpreting test results.
Reference:
Wynn J, Hoskovec J, Carter RD, Ross MJ, Perni SC. Performance of single‐gene noninvasive prenatal testing for autosomal recessive conditions in a general population setting. Prenat Diagn. 2023;1‐11