Category Archives: Triple Test

Triple Test

Screening for Down syndrome in the United States

This year marks the 30th anniversary of the use of laboratory tests to screen pregnancies for Down syndrome. The tests have evolved over the last three decades and as have their ability to detect affected fetuses. Currently there are several different lab tests available to screen for Down syndrome during pregnancy, including the recently developed cell-free DNA tests (commonly referred to as non-invasive prenatal testing, or NIPT).

How has the landscape of Down syndrome screening evolved over the last few decades? That was the question considered by investigators of a recent report that sought to determine the number of women screened for Down syndrome in the United States in 2011 and 2012, along with the type of test they received.

The results of this report were based on surveys completed by 168 laboratories that offered Down syndrome screening tests in 2011 and/or 2012 and are rather interesting:

  • Of the 4.13 million pregnancies that occur each year in the United States, approximately 72% are screened for Down syndrome.
  • The most common screening test is the quadruple test (50%) followed by the first-trimester combined test (18%), and the sequential test (14%). The other types of tests (e.g. triple test, full integrated test, and serum integrated test) were less commonly performed.
  • The 6 largest laboratories (those that screened more than 100,000 pregnancies each year) performed 61% of all screening tests.
  • The 32 smallest laboratories (those that screened fewer than 1,500 pregnancies each year) performed only 1% of all screening tests.
  • Between 2011 and 2012, the use of the first trimester and integrated testing increased by 27% and 6% and the use of the quad test decreased by 1.2%.
  • As shown in the figure below, there was an inverse relationship between the percent of laboratories that offered testing only in the second trimester (e.g. triple or quadruple tests) and the number of pregnancies screened each year.

Labs offering only 2nd trimester tests

That last bullet point is an important one because nearly 70% of women have their first prenatal visit in the first trimester and it is recommended that integrated screening be offered at this visit. However, because the number of laboratories offering only second trimester testing is much greater than the number of labs that offer all types of screening tests, this recommendation may not be easily adopted.

The Triple Test: time to say good bye

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:

  1. 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%.
  2. 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.
  3. 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.