Stability of inhibin A and unconjugated oestriol in the second trimester of pregnancy.

Background: The introduction of a second trimester quadruple test for fetal Down's syndrome adds the measurement of serum inhibin A (InhA) and unconjugated oestriol (UE3) to the existing repertoire of alphafetoprotein and intact human chorionic gonadotrophin. The aim of this study was to assess the stability of InhA and UE3 in whole blood and serum.

Methods: To determine whole blood stability, five extra blood specimens were obtained from each of 10 women attending an antenatal clinic. Samples were stored at room temperature for either two hours, one, three, five or seven days and centrifuged prior to analysis. Serum stability was studied by the analysis of surplus serum from 14 routine second trimester screening samples: seven stored at room temperature and seven stored at 4°C. An aliquot from each specimen was analysed two hours, one, three, five or seven days post centrifugation. Specimens were analysed for InhA and UE3 using the Beckman Access 2(®) Immunoassay analyser.

Results: No significant difference (P > 0.05) was shown in InhA or UE3 concentrations between the initial time point on the day of venepuncture and each of the subsequent analyses at one, three, five and seven days following collection for either whole blood or serum.

Conclusions: InhA and UE3 are stable in whole blood and serum for seven days.