ESTRIOL, UNCONJUGATED (uE3)

CLINICAL UTILITY:

The presence of unconjugated estriol in maternal serum is due primarily to the secretion of estriol by the fetal liver and placenta. Estriol precursors, cholesterol and pregnenolone are derived from the mother and the placenta. The fetal adrenal glands convert pregnenolone to dehydroepiandrosterone (DHEA), which is then converted to 16-OH-DHEA-sulfate by the fetal liver. The sulfated derivative then passes to the placenta where it is converted to estriol and enters the maternal plasma. Once in the maternal circulation its half-life is approximately 20 minutes before conjugation in the liver.

Estriol comprises 90% of the circulating estrogens in normal pregnancies. Determining the serum levels of the unconjugated form provides a sensitive indicator of fetal well-being and placental function.

Estriol in combination with bHCG and AFP and several maternal factors including gestational age, maternal age, race, weight, and diabetes can be used to estimate the prenatal risk for Down syndrome. Risk calculations can be calculated on specimens collected from 15 – 20 weeks gestation. These calculations are performed by the AFP Expert computer program (Benetech, Toronto, Canada).

METHOD DESCRIPTION:

The Estriol (Unconjugated) assay is a competitive binding immunoenzymatic assay.

REFERENCE RANGE:

Estriol results do not have a reference range. The are used as one factor in a multivariant analysis to calculate the prenatal risk of Down syndrome.

SPECIMEN REQUIREMENTS:

Serum (2.0 ml - min volume 1.0 ml), collected between 15-20 weeks gestation is the preferred specimen type.