Not everybody is a big fan of being poked with needles to have their blood drawn. But from a medical perspective, blood tests are far less invasive and carry less potential for harm than other diagnostic tools. That's why medical researchers are increasingly hunting for reliable blood tests for serious diseases, like the experimental Alzheimer's disease test we covered last week. And this week, researchers report progress on assessing a new condition: a promising blood test for determining Down syndrome in a fetus.
The technique involves a blood test for the mother and an ultrasound for the baby. From the combined results, doctors can estimate the chance that the baby has Down's. [CBS News]
Down syndrome happens when a baby has an extra copy of chromosome 21. Because the fetus' DNA can cross over into the plasma of the mother, doctors can seek out the extra chromosome in a blood sample taken from the mother. The researchers reporting in the British Medical Journal
say that in a pool of 753 women, their tests had no false negatives. It accurately found all 86 fetuses with Down (The women selected were all at high risk for down in their fetus; the prevalence among the general public is only about 1 in 800). That's a larger pool of women sampled than in similar research we covered in 2008
, and with a higher success rate. The test is not perfect, though: It also identified false positives for Down in 2 percent of the fetuses that did not have the syndrome, which is why even a test more accurate than this one must have a backup to verify positive results.
The false positive rate could be higher in lower-risk women, which means that any positive test result might still need to be verified with a definitive result -- a drawing of amniotic fluid to look at the fetus's chromosomes themselves -- before a woman makes a decision about whether to continue the pregnancy. [Boston Globe]
A blood for Down syndrome would be hugely welcome:
Currently, women in the United States are offered a blood test combined with an ultrasound test -- called the combined test -- to assess the risk of Down syndrome in pregnancy. The combined test still leaves an estimated 3% to 5% of women in need of invasive testing. [Los Angeles Times]
The invasive testing for Down often includes amniocentesis—drawing amniotic fluid for testing. That method carries with it an approximately 1 percent chance for miscarriage. Related Content: 80beats: New Prenatal Test for Down Syndrome Could Erase Miscarriage Risk
Gene Expression: Down Syndrome and Abortion Rates