Journal of Medical Biochemistry (Jan 2010)
Effects of serum-clot contact time on second-trimester prenatal screening markers and their stability in serum
Abstract
Alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol are screening markers for fetal trisomies and structural disorders of the neural tube defect type. Determination of these biochemical markers is per for med in laboratories that receive samples, serum or blood, and sample preparation as well as transport conditions may affect analyte stability and test results. The effect of serum-clot contact time prior to centrifugation (30, 60, 90, 120 minutes and 24 hours) was examined for serum values of alpha-fetoprotein, human chorionic gonadotropin and unconj ugated estriol, as well as their stability in serum samples over periods of up to five days at 2-8°C, and 30 days at -20°C. No statistically significant difference was found for analyte values in serum obtained by centrifuging blood samples after serum-clot contact times of 30, 60, 90 and 120 minutes at room temperature and 24 hours at 2-8°C, i.e. there is a 24-hour tolerance for prolonged serum-clot contact. Alpha-fetoprotein and free estriol serum values do not show statistically significant changes over a period of 5 days at 2-8°C. Similarly, serum freezing does not affect alpha-fetoprotein and free estriol values. As for human chorionic gonadotropin values showing statistical differences where serum is stored at both +4°C and at -20°C, their levels are concentration-dependent. Free estriol serum values at +4°C over the time period of 5 days showed statistically significant differences.
