Prevalence of primary aldosteronism among Asian hypertensive patients in Singapore

Recent studies using the ratio of plasma aldosterone concentration (PAC) to PRA as the screening test for primary aldosteronism in hypertensive popula tions suggested that the prevalence may be as high as 5-15%, with well over half of the subjects having normal serum potassium concentrations. Despite an increasing clinical awareness of this entity, many clinicians are reluc tant to consider routine screening for primary aldosteronism in essential h ypertensive patients because there are few community-based prevalence studi es of primary aldosteronism in different populations. Furthermore, genetic and environmental differences may affect the prevalence and presentation of primary aldosteronism in distinct populations. This study was designed to determine the prevalence of primary aldosteronis m in the predominantly Chinese population in Singapore. Three hundred and f ifty unselected adult hypertensive patients attending two primary care clin ics had random ambulatory measurements for PAC (nanograms per dL) and PRA ( nanograms per mL/h). Serum urea, creatinine, and electrolyte measurements w ere obtained simultaneously. Subjects with renal insufficiency (serum creat inine, >140 mu mol/L) and those treated with glucocorticoids or spironolact one were excluded. Screening was considered positive if the PAC: PRA ratio was more than 20 and the PAC was more than 15 ng/dL (>416 pmol/L). Primary aldosteronism was confirmed with the determination of PAC after 2 L saline administered iv over 4 h. Adrenal computed tomographic (CT) scans were perf ormed in biochemically confirmed cases of primary aldosteronism. Further lo calization with adrenal vein sampling was carried out in selected patients with equivocal findings on adrenal CT scan. Sixty-three (18%) of the 350 hypertensive patients (215 women and 135 men; age range, 23-75 yr) were screened positive for primary aldosteronism. Only 13 of these 63 subjects (21%) were hypokalemic (serum potassium, <3.5 mmol /L). Confirmatory studies were carried out in 56 (89%) of the subjects with a positive PAC:PRA ratio. Using a PAC above 10 ng/dL (>277 pmol/L) after s aline infusion as the diagnostic cut-off, 16 of the 56 patients had biochem ically confirmed primary aldosteronism. Hypokalemia was found in 6 of the 1 6 patients (37.5%) with primary aldosteronism. Subtype evaluation with adre nal CT scan and adrenal vein sampling indicated that half of the patients w ith primary aldosteronism may have had potentially curable unilateral adren al adenoma. Our data suggest that primary aldosteronism occurs in at least 5% of the ad ult Asian hypertensive population, and approximately half of these individu als may have potentially curable, unilateral, aldosterone-producing adrenal adenoma. Our findings also confirm the poor predictive value of hypokalemi a in both the diagnosis and the exclusion of primary aldosteronism.