PRIMARY HYPERALDOSTERONISM - A MISSED DIAGNOSIS IN ESSENTIAL HYPERTENSIVES

Background: It has been recognised recently that primary hyperaldoster onism may be more common than previously thought, the frequency of dia gnosis being improved by screening using a plasma aldosterone concentr ation to renin activity ratio. Aims: To determine the frequency of pri mary hyperaldosteronism, screening with both plasma aldosterone to ren in concentration (PRC) and activity (PRA) ratios, in normokalaemic sub jects previously diagnosed as having essential hypertension. Methods: Plasma potassium, aldosterone and PRCs and PRA and blood pressure (BP) were measured in 74 hypertensive subjects previously diagnosed by one physician as having essential hypertension. A normal range for plasma aldosterone/renin ratios was determined in 147 control subjects. Hype rtensive subjects with elevated aldosterone/renin ratios were further assessed for primary hyperaldosteronism using saline loading and fludr ocortisone suppression. Those in whom plasma aldosterone concentration exceeded 140 pmol/L after suppression tests underwent adrenal vein sa mpling for measurement of aldosterone and cortisol concentrations as w ell as adrenal CT scanning to diagnose the cause of primary hyperaldos teronism. The main outcome measures were a diagnosis of aldosterone pr oducing adenoma or bilateral adrenal hyperplasia based upon adrenal ve in sampling. Results: Four subjects (5%) had an elevated plasma aldost erone to renin ratio using PRC and six (8%) using PRA. Two subjects (2 .7%) in this selected population had primary hyperaldosteronism, both of whom had BP > 160/110 mmHg at the time of testing. Conclusions: The frequency of normokalaemic primary hyperaldosteronism appears to be g reater than previously thought, though the true incidence in the gener al population of hypertensive subjects remains unknown. The sensitivit y of diagnosis (but not specificity) may be improved by measurement of the plasma aldosterone/renin ratio and PRC is at least as adequate as PRA for this process.