Background: Classically, primary hyperaldosteronism was diagnosed in no more than 1% of patients with hypertension, when hypokalemia was used as the screening test. However, numerous patients with primary hyperaldosteronism do not have hypokalemia and the disease remains undiagnosed.
Aim: To assess the prevalence of normokalemic primary hyperaldosteronism among patients classified as having essential hypertension.
Patients and methods: One hundred hypertensive patients with a blood pressure over 145/95 were studied. Plasma aldosterone and plasma renin activity were measured in all. A primary hyperaldosteronism was diagnosed when high aldosterone levels (over 16 ng/dl) and low plasma renin activity (below 0.5 ng/ml/h) coexisted in two blood tests or the aldosterone/plasma renin activity ratio was over 50. A probable primary hyperaldosteronism was diagnosed when the ratio was between 25 and 50 and these patients were subjected to a Fludrocortisone test to confirm the diagnosis. A dexametasone suppression test was done to discard glucocorticoid remediable aldosteronism. An adrenal TAC scan was done to all patients with primary hyperaldosteronism.
Results: A diagnosis of primary hyperaldosteronism was reached in ten patients. Seven had elevated aldosterone and low plasma renin activity. In three the diagnosis was confirmed with the fludrocortisone test. All ten patients had normal serum potassium levels. Dexametasone suppression test was positive in three patients, that normalized their blood pressure levels. Adrenal TAC scans showed an adenoma in one patient and hyperplasia in another.
Conclusions: Primary hyperaldosteronism is more frequent than previously thought, it is overlooked when hypokalemia is used as the screening test and it can only be diagnosed measuring plasma aldosterone and renin activity.