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 (usually the second trimester).

Contents

[edit] Conditions detected

The most common abnormality the test can detect is fetal trisomy 21 (Down syndrome). In addition to Down syndrome, the triple and quadruple tests screen for fetal trisomy 18, 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.[1]

[edit] Values measured

The triple test measures the following three levels in the maternal serum: [2]

[edit] Interpretation

The levels may indicate increased risk for certain conditions:

Levels Associated conditions
Low values for AFP and UE3 and high values for hCG Down's Syndrome
Low levels of all three trisomy 18
High levels for AFP neural tube defects like spina bifida

An estimated risk is calculated and adjusted for the expectant mother's age;[3] 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,[4] and does not have nearly the same predictive power of amniocentesis or chorionic villus sampling. However, the screening test carries a much lower risk to the fetus, and in conjunction with the age-related risk by the patient is useful to indicate the need to proceed to the more invasive tests.

[edit] Variations

If only two of the hormones above are tested for, then the test is called a double test. In contrast, a quad test focuses on yet another hormone in addition. 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[5], because unconjugated estriol, the omitted hormone, is, in practice, not detected at a higher rate in people who have it, than in people without[5].[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."[6] Other names used include "quad test", "quad screen", or "tetra screen."

[edit] References

  1. ^ Benn PA (2002). "Advances in prenatal screening for Down syndrome: I. general principles and second trimester testing". Clin. Chim. Acta 323 (1-2): 1–16. doi:10.1016/S0009-8981(02)00186-9. PMID 12135803. 
  2. ^ Ball RH, Caughey AB, Malone FD, et al (2007). "First- and second-trimester evaluation of risk for Down syndrome". Obstet Gynecol 110 (1): 10–7. doi:10.1097/01.AOG.0000263470.89007.e3. PMID 17601890. 
  3. ^ Downs Syndrome Screening at Nottingham City Hospital. Retrieved on 2007-12-20.
  4. ^ Lamlertkittikul S, Chandeying V (2007). "Experience on triple markers serum screening for Down's syndrome fetus in Hat Yai, Regional Hospital". J Med Assoc Thai 90 (10): 1970–6. PMID 18041410. 
  5. ^ a b gpnotebook
  6. ^ Wald NJ, Morris JK, Ibison J, Wu T, George LM (2006). "Screening in early pregnancy for pre-eclampsia using Down syndrome quadruple test markers". Prenat. Diagn. 26 (6): 559–64. doi:10.1002/pd.1459. PMID 16700087. 

[edit] External links


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