Triple test

The triple test, also called triple screen, the Kettering test or the Bart's test, is an investigation performed during pregnancy in the second trimester to classify a patient as either high-risk or low-risk for chromosomal abnormalities (and neural tube defects).

The term "multiple-marker screening test" is sometimes used instead.^[1][2] This term can encompass the "double test" and "quadruple test" (described below).

The Triple screen measures serum levels of AFP, estriol, and beta-hCG, with a 70% sensitivity and 5% false-positive rate. It is complemented in some regions of the United States, as the Quad screen (adding inhibin A to the panel, resulting in an 81% sensitivity and 5% false-positive rate for detecting Down syndrome when taken at 15–18 weeks of gestational age)^[3] and other prenatal diagnosis techniques, although it remains widely used in Canada^[4] and other countries. A positive screen indicates an increased risk of chromosomal abnormalities (and neural tube defects), and such patients are then referred for more sensitive and specific procedures to receive a definitive diagnosis, often prenatal diagnosis via amniocentesis, although the stronger screening option of cell-free fetal DNA screening (also popularly known as noninvasive prenatal screening) is frequently offered. The Triple test can be understood as an early predecessor to a long line of subsequent technological improvements. In some American states, such as Missouri, Medicaid reimburses only for the Triple test and not other potentially more accurate screening tests, whereas California offers Quad tests to all pregnant women.^[5]

While the triple test can be performed at any point between 15 and 21.9 weeks of gestation, the highest detection rate for open neural defects is given by a test performed between 16 and 18 weeks of gestation.^[6]