Does the patient have hyperaldosteronism?
Spontaneous or diuretic-induced hypokalaemia has traditionally been considered a useful diagnostic guide for hyperaldosteronism in hypertensive patients. However, it has become apparent that up to 50% of subjects with primary hyperaldosteronism are normokalaemic (Gordon 1994). Moreover, the use of ACE inhibitors for hypertension elevates plasma potassium and might disguise underlying hyperaldosteronism. Therefore a high degree of clinical suspicion is required for diagnosis and hypokalaemia can no longer be considered a sufficiently sensitive diagnostic tool. The use of random aldosterone/renin ratios as a first line test is becoming more established and is probably less affected by drug therapy, day and diurnal variation and patient position that either aldosterone or renin alone (McKenna et al 1991). The use of a ratio also helps to diagnose those subjects with early adenomatous hyperaldosteronism in whom the renin is suppressed but with a still “normal” plasma aldosterone concentrat
