Use of polyethylene glycol in radioimmunoassay of human placental lactogen.

We describe a rapid radioimmunoassay for human placental lactogen in biological fluids, with use of polyethylene glycol to separate free from antibody-bound placental lactogen. The standard curve obtained, easily fitted to a logit-log transformation, is useful over a concentration range of 6 to 400 ug/liter. Within-assay variability is 1.97%, between-assay variability 2.20%. The relation is linear when lactogen added is plotted against that accounted for analytically, the actual recovery being 100.26%.