ESTRIOL, UNCONJUGATED, SERUM
- ESTRIOL, UNCONJUGATED, SERUM
- Start Date
- Expiration Date
- Estriol, E3, Unconjugated Estriol
- CPT Codes
- Reference Test
- ATLAS Test Code
- Transport Info
- Fasting Required?
- Patient Instructions
The specimen needs to be collected between the 14th and 22nd week of gestation for proper risk analysis.
- Reference Range
Unconjugated estriol is only seen in pregnancy and concentrations vary depending on gestational age and other factors
Non-pregnant values are typically less than 0.25 ng/mL
Quantitative Chemiluminescent Immunoassay (CLIA)
Most of the estriol circulation or excretion during the third trimester of pregnancy is the joint production of fetus and placental, originating from a precursor synthesized in the fetus by the adrenal glands, and transformed by the fetal level and the placenta into estriol. On traversing the placenta, this is rapidly metabolized, primarily in the maternal liver, to conjugated forms: the estriol sulfates and glucuronides. As a result, “free” estriol, the unconjugated form, accounts for barely nine percent of the total estriol in circulation; the estriol sulfates, which are relatively long-lived, account for roughly half. Urinary estriol consists entirely of conjugated forms since only free estriol enters the maternal circulation while only the conjugated forms are excreted. Normally, as the fetus develops, estriol production increases, resulting in a nearly three-fold rise in circulation estriol levels during the final trimester, and a corresponding increase in urinary levels. There is typically a surge at about the 36th week. According to the literature, free and total estriol concentrations reach approximately 15 and 250 ng/mL at term, while urinary output climbs to approximately 45 mg/day. After 40 weeks, estriol levels subside, declining by roughly 12 percent a week.