Particle-counting immunoassay of human somatotropin.

Human somatotropin was assayed by a novel automated nonradioisotopic technique, "particle-counting immunoassay," that requires a 45-min incubation and only 60 microL of 10-fold diluted sample. The principle of the assay is agglutination of antibody-coated latex particle by somatotropin, the reaction being measured by the (instrumented) counting of residual non-agglutinated particles. The dynamic range in serum extends from 0.2 to 40 micrograms/L. The between-assay CV was 12% for a concentration of 3.3 micrograms/L and 8.5% for 31.9 micrograms/L. The coefficient of correlation (r) with radioimmunoassay was 0.97. Curves for various dilutions of the macromolecular and monomeric forms of the hormone were not parallel.