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Cell-Free DNA Testing for Trisomies 21 & 18 Seems More Reliable Than Standard Screens — Physician’s First Watch

Medical News |
February 27, 2014

Cell-Free DNA Testing for Trisomies 21 & 18 Seems More Reliable Than Standard Screens

By Allison Bryant, MD, MPH

Cell-free DNA (cfDNA) screening has lower false-positive rates than standard screening for trisomies 21 and 18 in a general obstetric population, according to a New England Journal of Medicine study.

An industry-supported study enrolled some 1600 average-risk women at 21 general prenatal care centers to evaluate cfDNA's performance relative to standard aneuploidy screens, primarily in detecting trisomies 21 and 18.

cfDNA testing had significantly lower false-positive rates than did standard screening (0.3% vs. 3.6 % for trisomy 21 and 0.2% vs. 0.6% for trisomy 18). Positive predictive values of cfDNA testing for trisomies 21 and 18 were 45.5% and 40.0%, respectively — 10 and 5 times higher than those of standard screens. The overall negative predictive value of either test was 100%.

We must be wary: The false-positive rates, while vastly improved over those of traditional screens, are still not trivial — and other (albeit less common) genetic abnormalities are not detectable with cfDNA technology.

Dr. Bryant is an associate editor for NEJM Journal Watch Women's Health, from which this article is adapted.

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