1. The sensitivity and specificity of several individual and combined measurements for the diagnosis of primary aldosteronism have been calculated in 22 patients with established primary aldosteronism and 140 essential hypertensive controls.
2. Excellent sensitivity and specificity (93-100%) in the diagnosis of primary aldosteronism cannot be accomplished with any single test but can be achieved with combinations of (a) a low ‘stimulated’ plasma renin activity (PRA) (after frusemide and orthostasis) together with either hypokalaemia or a high ‘stimulated’ plasma aldosterone concentration (above 944 pmol/l), or (b) a low ‘stimulated’ PRA, together with either hypokalaemia or a high saline-suppressed plasma aldosterone concentration (above 236 pmol/l), or (c) a pressor response to saralasin together with elevated values of NaCl-suppressed or frusemide-stimulated plasma aldosterone concentration. Procedures (a) or (c) can be completed in 3–4 h; (b) requires 8 h.