Friday, October 21, 2011

some Utah doctors are cautious about using Sequnom's MaterniT21 test

Salt Lake City is one of 20 national launching sites for a new blood test to detect Down syndrome in the womb. But some Utah doctors are cautious about using it, including the Salt Lake City physician who participated in a study showing how the blood test works.

San Diego-based company Sequnom, Inc., launched the MaterniT21 test this week, touting it as a way to better screen for Down syndrome and reduce the need for invasive diagnostic tests that pose a risk of miscarriage.

Using blood drawn from the mother, the new test measures circulating cell-free DNA to detect Trisomy 21, the most common chromosomal anomaly that causes Down syndrome. It can be done as early as 10 weeks with results in about 10 days, according to the company.

The test was launched in 20 cities — large metropolitan areas and those with high birth rates like Salt Lake City. The test must be ordered by a physician, and it’s meant for women at high risk of having a baby with the disorder — those who are 35 years and older or who have an ultrasound showing fetal anomalies, for example.

The company estimates the test would cost insured patients $235.

But Intermountain Healthcare facilities will not be using MaterniT21 yet, said physician Nancy Rose, director of reproductive genetics for the hospital system, even though Intermountain and Salt Lake City-based ARUP participated in a study of the blood test that Sequnom is using to bolster claims that it works.

"I don’t think it’s ready for prime time," said Rose, noting that she participated in the industry-funded study because it was overseen by Brown University. "This study has proven that it works in a certain population of patients, but that’s a long way from actually implementing it in your clinic. What does it cost? Will insurance cover it? What do we know about its effectiveness? If someone screens negative, is that good enough?"

Rose noted that the new test doesn’t detect other chromosomal abnormalities like spina bifida, while traditional screening tests do. And it hasn’t been proven useful among low-risk women, the majority of pregnant women, she said.

The study, published this week in Genetics in Medicine, included 4,600 high-risk women from 27 sites (including 78 Utahns). Among the 1,600 women on whom the genetic test was used, MaterniT21 detected Down syndrome with 99 percent accuracy with one false positive and two false negatives.

The fact that there were only three wrong results shows "that this test is actually ready for prime time," said physician Mathias Ehrich, Sequenom’s senior director of research and development. He acknowledged some details need to be worked out, including whether it will work on heavier women (13 samples couldn’t be analyzed because the percentage of fetal DNA in the mothers’ blood was too low).

Still, "It’s a young but not immature field," he said. "The test has certainly withstood all the necessary validations you need in order to implement it."

Existing screening tests — which combine ultrasound with maternal blood tests — have lower accuracy rates with higher false positive rates, according to the study. That means more women may go on to get amniocentesis or chorionic villus sampling, the study said. Those tests, which involve sampling amniotic fluid or placental tissue, can cause miscarriages in up to one of 200 procedures.

Ehrich said women now can take the MaterniT21 test before the invasive tests if the screening tests show they are at risk. If the genetic test comes back negative, he said doctors would "most likely" not recommend an amnio or CVS. If MaterniT21 is positive, women who want confirmation would need one of the invasive tests.

Physician Robert Silver, chief of the University of Utah’s maternal fetal medicine program for high-risk women, sees value in using MaterniT21 as a second screen. He noted that women who seek confirmation aren’t always doing it to terminate the pregnancy. They want to rule out a problem or prepare themselves emotionally for a child with special needs.

Women, he noted, are anxious about the invasive diagnostic tests. "The emotional baggage of potentially harming a normal baby is very difficult for families. There’s a lot of potential and certainly a desire to have a test like this," he said. "The downside is the test has not been perfected."

1 comment:

  1. I have doubts too. I wrote about them in my article here.