Comparison of a Biological and an Immunological Assay for the Measurement of Plasma Renin Activity

The present study was undertaken to compare the values of plasma renin activity measured by both a bioassay (Skinner method) and by a radioimmunoassay procedure (Haber method). In 28 normal subjects, mean immunoassayable plasma renin activity (PRA) of 1.2 ng/ml/hr ± 0.1 se was not significantly different from the mean normal value of 1.3 ng/ml/hr ± 0.1 se determined by bioassay. Similarly, of 26 patients with either essential or renovascular hypertension, peripheral venous PRA measured by immunoassay did not differ from that determined by bioassay (p > 0.30). The correlation coefficient of 0.97 obtained by comparing the values from the 2 methods was highly significant (p < 0.001). In 6 of 18 patients being evaluated for renovascular hypertension, PRA in plasma from the vein of the affected kidney was at least 1.5 times that in plasma from the contralateral renal vein with both renin methods. Eleven patients had a renal venous renin ratio of less than 1.5 with both methods. In one patient, renin activity was undetectable in both renal veins by bioassay, and although PRA in the right renal vein was twice that in the left by radioimmunoassay, both values were in the lownormal range. Of 39 patients with severe chronic renal insufficiency, there was again a significant correlation between the 2 methods (p < 0.01), and the mean PRA values did not differ (p > 0.30). Renin disappearance curves with both methods were similar in each of 2 patients following bilateral nephrectomy. In 2 groups of dogs, a significant correlation between both renin methods was demonstrated in response to hemorrhage and in response to furosemide induced diuresis (p < 0.01) ; the actual values measured by the 2 methods were not significantly different. Overall, these results demonstrate a close correspondence between the renin activities determined by the Haber radioimmunoassay and Skinner bioassay procedures. However, in a number of individual instances, the correspondence was relatively poor.