A recent post in the NACB blog titled "Jurassic Lab" invited readers to comment on which laboratory tests they thought should be considered obsolete. I suggested that the Triple Test, a blood test used during the second trimester of pregnancy to screen for Down syndrome, should go the way of the dinosaur.
Labs that offer Down syndrome screening tests should seriously consider taking the Triple Test off of their menus. Why? There are a few reasons:
- It is not a great test. As a screening test for Down syndrome, the Triple test is only okay. If I were grading it, then I would give it a C. It detects about 70-75% of fetuses with Down syndrome and it has a false-positive rate of 5-8%.
- Better tests are available. I've already wrote about the different types of Down syndrome screening tests. Other tests, like the Quad and the Integrated tests perform much better than the Triple test. Given a choice, I imagine most mothers-to-be would prefer to have the best screening test available. It's abundantly clear that of all the tests used to screen for Down syndrome, the Integrated test is best. It has a detection rate of about 90-95% and (importantly) a false-positive rate that is lower than the Triple test. A low false-positive rate is important because it decreases the number of unnecessary invasive diagnostic procedures that are performed due to an abnormal result from a screening test.
- Lack of recommendation. Several national guidelines no longer recommend use of the Triple test and recommend better performing screening tests instead.
Clearly the Triple test is irrelevant. That doesn't mean that all the doctors that order Down syndrome screening tests have gotten the message. A 2009 survey of obstetricians in the US revealed that nearly a quarter of them (23%) continued to use the Triple test. That's lower than it used to be but still rather high for a test that shouldn't be ordered. Until laboratories that offer the Triple test take it off of their menus, it will continue to be (inappropriately) utilized.