THE STABILITY OF hCG AND FREE β-SUBUNIT IN SERUM SAMPLES

✍ Scribed by ANDREW KARDANA; LAURENCE A. COLE

• Book ID: 101236042
• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 245 KB
• Volume: 17
• Category: Article
• ISSN: 0197-3851
• DOI: 10.1002/(sici)1097-0223(199702)17:2<141::aid-pd47>3.0.co;2-i

✦ Synopsis

Human chorionic gonadotropin (hCG) free -subunit measurement is used as a screening test for Down syndrome pregnancies. Use, shipping, and storage conditions have, however, to some extent been limited by a stability problem; the swamping of serum free -subunit levels by new molecules coming from the dissociation of hCG. We examined the stability of free -subunit levels in six fresh serum samples from the first trimester of pregnancy. The mean hCG level in the fresh serum samples was 3710 886 g/l; this included a 3•0 0•39 per cent nicked hCG component. The mean free -subunit level was 0•27 0•04 per cent and the nicked free -subunit level was 0•10 0•04 per cent of the hCG concentration. Samples were incubated for 0, 0•5, 1, 2, and 4 weeks at 21 C, with no additives. After half a week, the free -subunit level rose to 137 17 per cent, and after 4 weeks to 360 53 per cent of the starting level (ANOVA P^0•05). Parallel, but greater, increases were observed in nicked hCG and nicked free -subunit levels. The experiment was repeated with the addition of penicillin-streptomycinfungizone to fresh serum. After half a week, the free -subunit level increased to only 101 3•0 per cent (t-test, with/without additive, P^0•05), and after 4 weeks to only 136 7•8 per cent (P^0•05) of the starting level. At 4 weeks, nicked hCG production was reduced from 499 83 to 158 15 per cent of the starting level. We infer that nicking of hCG and dissociation of unstable nicked hCG may be pathways supplementing free -subunit in serum samples. We further infer that hCG nicking activity comes from microbes, and that free -subunit levels can be stabilized for shipping and longer storage by antibiotic/antimycotic additives. 1997 by John Wiley & Sons, Ltd.