Triple test

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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. The Triple test measures serum levels of AFP, estriol, and beta-hCG, with a 70% sensitivity and 5% false-positive rate. It is now nearly obsolete in some regions of the United States, replaced by the Quad test (81% sensitivity and 5% false-positive rate by adding inhibin A to the panel) and more sophisticated and sensitive prenatal diagnosis, although it remains widely used in Canada^[1] and other countries. These tests classify a patient as either high-risk or low-risk for chromosomal abnormalities (and neural tube defects); high-risk patients are then referred for an invasive procedure such as an amniocentesis to receive a definitive diagnosis. 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. ^[2] Direct testing of fetal DNA in maternal blood may simplify current screening programs.^[3]

Contents 1 Conditions screened 2 Values measured 3 Interpretation 4 Variations 4.1 Double test 4.2 Quadruple test 5 References 6 See also 7 External links

[edit] Conditions screened

The most common abnormality the test can screen is trisomy 21 (Down syndrome). In addition to Down syndrome, the triple and quadruple tests screen for fetal trisomy 18 also known as Edward's syndrome, open neural tube defects, and may also detect an increased risk of Turner syndrome, triploidy, trisomy 16 mosaicism, fetal death, Smith-Lemli-Opitz syndrome, and steroid sulfatase deficiency.^[4]

[edit] Values measured

The triple test measures the following three levels in the maternal serum: ^[5]

• alpha-fetoprotein (AFP)
• human chorionic gonadotropin (hCG)
• unconjugated estriol (UE₃)

[edit] Interpretation

The levels may indicate increased risk for certain conditions:

AFP	UE3	hCG	Associated conditions
low	low	high	Down Syndrome
low	low	low	trisomy 18 (Edward's syndrome)
high	n/a	n/a	neural tube defects like spina bifida associated with increase levels of acetylcholinesterase in aminonic fluid, or omphalocele, or gastroschisis, or multiple gestation like twins or triplets

An estimated risk is calculated and adjusted for the expectant mother's age;^[6] if she's diabetic; if she's having twins or other multiples, and the gestational age of the fetus. Weight and ethnicity may also be used in adjustments.^{[citation needed]} Many of these factors affect the levels of the substances being measured and the interpretation of the results.

The test is for screening, not for diagnosis,^[7] and does not have nearly the same predictive power of amniocentesis or chorionic villus sampling. The screening test carries a much lower risk to the fetus, however, and in conjunction with the age-related risk of the patient it is useful to help determine the need for more invasive tests.

[edit] Variations

If only two of the hormones above are tested for, then the test is called a double test. A quad test tests an additional hormone, inhibin. Furthermore, the triple test may be combined with an ultrasound measurement of nuchal translucency.^{[citation needed]}

[edit] Double test

Only AFP and hCG are measured. However, the maternal age, weight, ethnicity etc. are still included. A double test is almost as effective as a triple test^[8], because unconjugated estriol, the omitted hormone, is, in practice, not detected at a higher rate in people who have it than in people without^[8].^{[citation needed]}

[edit] Quadruple test

A test of levels of dimeric inhibin A (DIA) is sometimes added to the other three tests, under the name "quadruple test."^[9] Other names used include "quad test", "quad screen", or "tetra screen."

[edit] References

[edit] See also

• Triple bolus test

[edit] External links

• AmericanPregnancy.org
• Risk and Down screening

v • d • e Obstetrical surgery and other procedures (ICD-9-CM V3 72-75) Delivery Induction · Episiotomy · Symphysiotomy · Caesarean section (Elective, On maternal request) · EXIT procedure Diagnostic sampling: Amniocentesis · Chorionic villus sampling · Triple test · Apt test imaging: Cardiotocography (Non-stress test) · Biophysical profile (Amniotic fluid index) · Fetoscopy · Nuchal scan challenge: Contraction stress test Intervention Fetal surgery obstetric navs: conditions, eponymous signs, proc