Active renin versus plasma renin activity to define aldosterone-to-renin ratio for primary aldosteronism

Background In recent years, the assessment of the plasma aldosterone-to-renin ratio (ARR) has become an established screening method for the diagnosis of primary aldosteronism. Plasma renin activity (PRA) is usually measured to define ARR although, increasingly, renin concentration alone is often measured in clinical routine. Objective To determine the threshold of ARR using active renin concentration to screen for primary aldosteronism. Design and participants To determine the ARR threshold based on plasma immunoreactive renin concentration 00, we measured plasma aldosterone concentration (PAC), irR and PRA in 36 hypertensive patients, nine thereof with adrenal adenoma, and compared ARRs calculated from irR and PRA, respectively. Setting Single-centre, hypertension clinic in a tertiary care hospital. Results PRA ranged from 0.41-14.9 ng/ml per h and irR from 1.1-72 ng/l. There was an excellent correlation between PRA and irR (r = 0.98, P < 0.0001) and between ARR(PRA) and ARR(irR) (r = 0.96, P < 0.0001). An ARR(PRA) > 750 pmol/l per ng/ml per h was previously found to be highly predictive of primary aldosteronism because 90% of the corresponding patients failed to suppress PAC upon saline infusion or fludrocortisone. The corresponding threshold value for ARR(irR) was 150 pmol/ng in our patients. Using these cut-offs, nine subjects had both increased ARR(PRA) and ARR(irR) while, in three patients, either ARR(PRA) or ARR(irR) were increased. The nine patients with increased ARR(PRA) and ARR(irR) also had PAC > 650 pmol/l. Only these patients had adrenal adenomas. Conclusions The ARR threshold to screen for primary aldosteronism may be based on measurement of irR. An ARR(irR) > 150 pmol/ng may indicate primary aldosteronism. (C) 2004 Lippincott Williams Wilkins.