Effects of Serum-Clot Contact Time on Second-Trimester Prenatal Screening Markers and their Stability in Serum

Effects of Serum-Clot Contact Time on Second-Trimester Prenatal Screening Markers and their Stability in Serum 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 performed 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 unconjugated 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. Uticaj Dužine Kontakta Koaguluma sa Serumom na Vrednosti Biohemijskih Markera Prenatalnog Skrininga Drugog Trimestra i Njihova Stabilnost u Serumu Alfa-fetoprotein, humani horioni gonadotropin i nekonjugovani estriol koriste se za skrining trizomija fetusa i strukturnih poremećaja tipa defekata neuralne tube tokom drugog trimestra trudnoće. Za određivanje ovih biohemijskih markera u laboratorije se šalju uzorci, serum ili krv, a način pripreme uzoraka, kao i uslovi tokom transporta mogu da utiču na stabilnost ispitivanih analita i rezultate testa. Ispitivan je uticaj dužine kontakta koaguluma sa serumom pre centrifugiranja (30, 60, 90, 120 minuta i 24h) na vrednosti alfa-fetoproteina, humanog horionog gonadotropina i nekonjugovanog estriola u serumu, kao i njihova stabilnost u uzorcima seruma tokom 5 dana na 2-8 °C i 30 dana na -20 °C. Utvrđeno je da nema statistički značajne razlike za vrednosti ispitivanih analita u serumu dobijenom centrifugiranjem uzorka krvi posle kontakta sa koagulumom u trajanju od 30, 60, 90 i 120 minuta na sobnoj temperaturi i 24h na 2-8 °C, odnosno da postoji tolerancija od 24h za produženi kontakt seruma sa koagulumom. Alfa-fetoprotein i slobodni estriol ne menjaju se statistički značajno u serumu tokom 5 dana na 2-8 °C. Zamrzavanje seruma takođe ne utiče na vrednosti alfa-fetoproteina i slobodnog estriola. Vrednosti humanog horionog gonadotropina, čuvanjem seruma na +4 °C i na -20 °C, menjaju se statistički značajno, ali različito u zavisnosti od koncentracije. Za slobodni estriol u serumu na +4 °C, tokom 5 dana, dobijene su statistički značajne razlike.