Use of inorganic salts to minimize serum interference in a sandwich enzyme immunoassay for human growth hormone using Fab'-horseradish peroxidase conjugate.

In a sandwich enzyme immunoassay (EIA) for human growth hormone (hGH) with anti-hGH Fab'-peroxidase conjugate, the effects of inorganic salts on serum interference were examined, and serum interference was eliminated by incubation of serum samples with anti-hGH IgG-coated polystyrene balls in the presence of 0.4 mol/l NaCl, avoiding the need for hGH-free serum. The sensitivity for hGH was 60 fg/tube or 3 ng/l of serum. No cross-reaction was observed with prolactin, chorionic gonadotropin or luteinizing, thyroid-stimulating and follicle-stimulating hormones. The coefficients of within-assay and between-assay variations were 2.8-6.5% and 4.8-8.7%, respectively. The regression equation and correlation coefficient to radioimmunoassay (RIA) were y(EIA) = 0.89x(RIA) + 0.11 and 0.98 (n = 100), respectively. hGH levels in normal male and female adult serum taken between 9:00 and 10:00 a.m. after overnight fasting and 1 h rest were 312 ng/l (range 53-940 ng/l; n = 10) and 662 ng/l (112-2195 ng/l; n = 13), respectively.