Validation of a New Automated Renin Assay

BACKGROUND: Measurement of plasma renin is important for the treatment of patients with congenital adrenal hyperplasia (CAH) and in the evaluation of patients with suspected hyperaldosteronism. Immunologic assays for plasma renin offer easier implementation and standardization than enzyme-kinetic assays for plasma renin activity, but their sensitivity and specificity have been questioned. We studied a renin immunochemiluminescence assay on an automated platform. METHODS: Renin was measured by an enzymatic assay, by IRMA, and by the new Nichols Advantage Specialty System immunochemiluminometric assay (ICMA), in plasmas from unselected individuals from our outpatient departments and in samples from patients with selected diagnoses. RESULTS: The detection limit in the ICMA was 0.1 mU/L. The recovery was >90%, and the imprecision (CV) was generally <9%. Mean (SD) concentrations measured by ICMA were 32 (21)% lower than those measured by IRMA. Renin concentrations as measured by ICMA were identical in serum and EDTA-, heparin-, and citrate-anticoagulated plasmas. Prolonged incubation of whole blood at room temperature before centrifugation did not affect renin concentrations. The central 95% interval for 80 healthy adults was 6-85.5 mU/L. Plasma renin as assessed by ICMA in patients with primary hyperaldosteronism was <0.2 mU/L. CONCLUSIONS: The performance characteristics of the new renin ICMA allow its use for patients with CAH and for the diagnosis of mineralocorticoid hypertension. In view of the variability of renin concentrations, use for other forms of hypertension or physiologic research calls for the development of uniform sampling protocols.