Recent reports have indicated that substances such as arginine, leucine, epinephrine and heparin artifactually alter the radioimmunoassay measurement of insulin. To further evaluate this problem fifty-eight plasma samples were enriched with arginine, fifty-eight samples with leucine and 141 samples with epinephrine, and all were assayed for insulin by a double antibody radioimmunoassay technic. Addition of these substances resulted in no alteration in insulin measurements. Arginine, leucine and epinephrine did not alter the measurement of insulin in standard solutions of human insulin. Also, 114 pairs of heparinplasma and serum samples were assayed for insulin, but no significant differences were noted. Heparin also had no effect on the measurement of standard solutions of human insulin. It is concluded that radioimmunoassay is capable of specifically measuring insulin levels in the presence of arginine, leucine or epinephrine. It also appears that either plasma or serum are equally suitable for insulin determinations. Comparison of our data with published reports from other laboratories indicate that there are differences in the specificity of radioimmunoassay methods used in various laboratories, and each laboratory must validate its own radioimmunoassay procedure.

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