Rossi GP, et al. - This study was undertaken to determine if aldosterone/renin ratio (ARR) values were affected by the mineralocorticoid receptor antagonist (MRA) canrenone and/or by canrenone plus olmesartan treatment in patients with primary aldosteronism (PA). Participants in the study were treated for 1 month with canrenone (50–100 mg orally), and for an additional month with canrenone plus olmesartan (10–20 mg orally). According to results, canrenone did not lower plasma aldosterone or increase renin, therefore, the high ARR and true positive rate remained unchanged. Canrenone did not preclude accurate diagnosis in patients with PA at doses that effectively regulated the serum potassium and blood pressure values. The addition of angiotensin type 1 receptor blocker olmesartan increased the false negative rate slightly. Thus, MRA did not seem to jeopardize the accuracy of PA diagnosis.