Cell Free DNA Screening is not a Simple Blood Test

A recent article in the Boston Globe presents a disturbing picture of prenatal testing, in a report describing how “Oversold prenatal tests spur some to choose abortions.” The article goes on to discuss prenatal screening with cell free DNA, and to present a number of patient cases in which the screening test indicated that a patient was at high risk for aneuploidy when in fact, the fetus was normal.

It is important for providers to remember that cell free DNA is a screening test, and does not have the diagnostic accuracy of amniocentesis.  By its very nature, a screening test does not tell with 100% certainty whether or not a fetus will be affected by a given disorder. Unfortunately, in part because of the high stakes in this very competitive market, the tests are being presented as having >99% accuracy, the same accuracy as is used to describe amniocentesis and CVS. 

While the detection rates for trisomy 21 are very high, and the false positive rate is very low, the test is less accurate and effective for detection...