At the Trisomy 18 Foundation, we work to educate healthcare professionals who are on the front lines of delivering a Trisomy 18 diagnosis. Last month, our Executive Director Victoria Miller spoke at the National Society of Genetic Counselors Conference in Seattle, Washington. We regularly build relationships with Genetic Counselors who are important allies in helping the Foundation ensure all parents have access to compassionate, knowledgeable care for their child diagnosed with Trisomy 18.
Victoria’s panel, “Challenges to Prenatal Cell-Free DNA Screening: The Patient Advocacy Perspective,” joined together leaders from a range of advocacy organizations devoted to helping patients cope with genetic conditions from Down Syndrome to Klinefelter Syndrome. Her talk focused on the problems with cell-free DNA (cfDNA) screening, otherwise known as non-invasive prenatal testing (NIPT) and questioned whether NIPT tests for Trisomy 18 and 13 are indeed more accurate than traditional screening methods. These screening tests–Harmony, Verifi, Panorama, and MaterniT21 are some examples–are touted by the labs who market them as more accurate than traditional screening like the Triple or Quad screening blood tests. The labs often cite data that show the tests to be 99% accurate. But are they really for Trisomy 18 and 13? We know that when it comes to the health and futures of our children, nothing is more important than accurate and reliable prenatal screening and testing when the stakes are so high.
Victoria’s talk pointed out the particular troubling problems with using cfDNA screening with Trisomy 18 and 13, and pointed to data that indicates what’s called the Positive Predictive Value (PPV) of the test that is actually much, much lower than the 99% accurate figure would suggest. PPV refers to the proportion of patients with positive test results who do, in fact, have the genetic condition being screened for.
To explain . . . a PPV of 80% tells you that of all the those receiving a “at risk/positive” screening result, that 80% of the time, a diagnosis of Trisomy 18 was accurate when an amniocentesis or CVS was performed to confirm. A PPV of 20% would mean only 20% of the time was the test’s prediction of Trisomy 18 accurate. When you factor in the additional costs for cfDNA test and the fact that a mother’s health insurance may not cover these costs, are these tests really adding additional value to warrant these higher, possibly out-of-pocket costs for Trisomy 18 and 13 conditions? The PPV for these screening tests vary widely in response to factors like the specific brand of test used, the mother’s age, and how far along she is in the pregnancy. (If you want to calculate your own PPV from a cfDNA test, National Society of Genetic Counselors provides an online PPV calculator.)
We know all too well that for parents undergoing cell-free DNA screening for Trisomy 18 or 13, that uncertainty is agonizing. But as Victoria’s talk showed, using the screening test diagnostically is a mistake. In fact, cell-free DNA screening tests are often no better than a coin toss for indicating whether a particular child is affected by Trisomy 18.
Victoria’s talk ended with a call for more research into the accuracy of these tests for Trisomy 18 and 13 specifically, and more focus on patient education and support. The patient’s voice is crucial in understanding these issues, and bringing your voices into those discussions is one of our most important duties on your behalf. That’s why It is so important that we work together to make sure that the diversity of all our families’ voices are part of these important conversations.