Radioimmunoassay of calcitonin in normal human urine

Direct radioimmunoassay of calcitonin in human urines containing < or = to 3 ng/ml. is complicated by interference from substances most probably structurally similar to the methylated xanthines. A simple, reproducible procedure is described for the removal of the interfering substances prior to radioimmunoassay. Utilizing this procedure and a sensitive antiserum specific for the carboxyl terminal region of calcitonin, it has been possible to obtain precise estimates of calcitonin concentrations in the urine over the range, 0.02 to 3.0 ng/ml within which calcitonin is found in normal urine. The intra- and interassay s/anti X were 5 and 15%, /sup 0/espectively. The urine calcitonin values apparently reflect serum calcitonin concentrations (e.g., urine/serum r = 0.9873 for 40 hypercalcitonemic patients); but urine calcitonin determination has two important advantages: greater reproducibility because of decreased heterogeneity and greater differentiation of patient populations. In view of these results, the assay of urine calcitonin may prove to be a very useful clinical tool.