The effect of thermal instability of intact human chorionic gonadotropin (ihCG) on the application of its free beta-subunit (free beta hCG) as a serum marker in Down syndrome screening.
The kinetics of free beta hCG concentrations were measured in 30 maternal whole blood samples from second-trimester pregnancies during 72 h incubation at 3, 20, and 30 degrees C. Dissociation of intact hCG (ihCG) was undetectable at 3 degrees C and produced a more than 20 per cent increase of free beta hCG at 20 degrees C and a more than 100 per cent increase at 30 degrees C. hCG dissociation at 30 degrees C was not reduced by a protease inhibitor (sodium iodoacetate) and also occurred in purified hCG dissolved in a protease-free incubation medium. These results were reproduced under conditions of sample transport by post at different environmental temperatures. In conclusion, reliable free beta hCG assessment requires that the specimen be kept cool from vene puncture until assay or completely other transport strategies have to be considered. Evaluation of free beta hCG as an effective marker in prenatal Down syndrome screening must be reconsidered from this aspect.
D001800:Blood Specimen Collection; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D004314:Down Syndrome / Q000097:blood / Q000175:diagnosis*; D004355:Drug Stability; D005260:Female; D006358:Hot Temperature; D006801:Humans; D007461:Iodoacetates / Q000494:pharmacology; D019807:Iodoacetic Acid; D007700:Kinetics; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011296:Prenatal Diagnosis; D011480:Protease Inhibitors / Q000494:pharmacology
D018997:Chorionic Gonadotropin, beta Subunit, Human; D007461:Iodoacetates; D011480:Protease Inhibitors; D019807:Iodoacetic Acid