Radioimmunoassay of basic somatomedin in human plasma and serum: effects of incubation time and temperature, and of anticoagulants.

Several different somatomedin radioimmunoassays have been described. This paper reports a study of the effects of various storage conditions and various anticoagulants on the results of one of these assays in plasma and serum. The amount of immunoreactive somatomedin measured in serum increased with the duration and temperature of incubation of the samples before the assay was done. Acidification of the samples, followed by lyophilization and reconstitution, eliminated this variability, enabling measurement of all the immunoreactive somatomedin. Heparin, in association with plasma or serum proteins, artefactually increased the amounts of immunoreactive somatomedin measured. Acidic gel filtration of heparinized plasma prior to the assay similarly enabled measurement of all the immunoreactive somatomedin.