A two-site monoclonal immunoradiometric assay for total renin protein: comparison with an established enzyme kinetic...

1. A two-site monoclonal immunoradiometric assay (IRMA) for total renin protein was established to cover the range 0.3-300 microIU. The limit of sensitivity was 2 microIU/ml plasma. 2. IRMA after acid activation of plasma prorenin gave the highest and most consistent values for total plasma renin (TPRC = 197 microIU/ml, s.e.m. = 22, in 17 normal adults). In untreated plasma, TPRC measured by IRMA was lower than expected, but in amniotic fluid expected values were obtained. 3. Human angiotensinogen at normal concentrations did not interfere with binding of renin to the first antibody, but ovine angiotensinogen displaced the standard curve significantly. 4. TPRC measured by IRMA is convenient and highly sensitive, but either the state of activation of the enzyme or another effect of acidification of plasma influences the estimated value. 5. Active renal renin may not be the appropriate reference standard for this IRMA unless plasma renin is previously activated.