Noninvasive prenatal testing (NIPT) has limitations in determining the risk of fetal aneuploidy, according to an article published Aug. 7 in Genetics in Medicine, the journal of the American College of Medical Genetics and Genomics.

The test method has produced strong results in some instances. In one study by Quest Diagnostics, NIPT demonstrated 100% sensitivity for trisonomy 21 and 18, yielding a specificity of greater or equal to 99.7% for each. Data from several independent groups, however, prompted the review of “the concordance of results among cases with positive or negative NIPT results referred to Quest Diagnostics for confirmation with cytogenic studies,” the article explains.

Researchers looked at results from more than 100 consecutive specimens that were either prenatally and/or postnatally studied by fluorescence in situ hybridization, karyotyping, and/or oligo–single-nucleotide polymorphism microarray.

True-positive rates varied among the cytogenic results. As an example, 38 of the 41 noninvasive prenatal testing cases for trisomy 21 were positive, yielding a true-positive rate of 93%. However, for trisomy 18, the true-positive rate was only 64%.

For trisomy 13 and sex chromosome aneuploidy, the true-positive rates were only 44% and 38%, respectively.

“These findings raise concerns about the limitations of noninvasive prenatal testing and the need for analysis of a larger number of false-positive cases to provide true positive predictive values for noninvasive testing and to search for potential biological or technical causes,” the article states.

Any NIPT findings should be carefully interpreted, the researchers suggest. “To an average clinician, the claim that a test is >99% specific leads him or her to expect that the false-positive rate will be <1%. As can been seen by the data in this report and others, the ability of NIPT to correctly predict a positive result for trisonomy 18 and trisonomy 13 is less than 60%.”

Providers and consumers alike should be aware that NIPT is just a screening test and is not a substitute for invasive prenatal diagnosis, the article notes.