Measurement of plasma renin concentration instead of plasma renin activity decreases the positive aldosterone-to-renin ratio tests in treated patients with essential hypertension

Background: The plasma aldosterone-to-renin ratio (ARR) for the diagnosis of primary aldosteronism is normally calculated with plasma renin activity (PRA) as denominator. However, new direct renin assays that measure plasma renin concentration (PRC) are progressively replacing PRA because these are faster, simpler, and more reproducible. Objective: To assess whether the calculation of ARR with a direct assay (ARRD, ng/dl/mU/l) instead of PRA (ARRP, ng/dl/ng/ml/h) affects the rate of positive tests in patients on liberal antihypertensive treatment. Design and participants: PRA, PRC, and plasma aldosterone concentration (PAC) were measured in 88 patients with essential hypertension, both in the supine position and after 60min of active standing while on treatment with a variety of antihypertensive medications. The same measurements were carried out, for comparison, in 10 patients with proven aldosterone-producing adenoma. Setting: Single center, outpatient hypertension clinic in a tertiary care hospital. Results: In patients with essential hypertension, median ARRP was 12 (range 0-71) in the supine position and 13 (range 0-80) after standing. The corresponding values of ARRD were 0.4 (range 0.01-3) and 0.5 (range 0.02-7.8). Between ARRP and ARRD, there was a linear, highly significant relationship both in supine and standing position (r=0.88 and r=0.92, respectively). Using as threshold of normalcy for ARRP a value less than 30, as it is recommended by guidelines, there were 13 (15%) and 18 (20%) false positives, respectively in supine and standing position, whereas with the threshold of 3.7 for ARRD, there were no false positives in recumbent position and four (5%) after standing. Accordingly, the specificity of ARRP was 0.85 and 0.78 and that of ARRD 1 and 0.95. In 10 patients with primary aldosteronism, median supine ARRP was 298 (range 48-1222) and ARRD 34 (range 2.8-244). Among these patients, no false negatives were found with ARRP and just one with ARRD. Conclusion: The rate of positive tests calculating ARR with PRC is lower than with PRA, the lower rate being found in patients studied in the recumbent position and apparently it is not affected by ongoing antihypertensive treatment.