Screening and diagnosis of primary aldosteronism

Primary aldosteronism (PA) is the commonest form of secondary hypertension in South Africa with an approximate prevalence of 7.5% in the primary-care setting. Hypokalaemia is a poor screening test with 70% of proven cases having normal serum potassium levels. The aldosterone/rennin ratio is a robust screening test with a high sensitivity and specificity, but in South Africa this should be combined with an absolute aldosterone level because of the high incidence of low-renin hypertension in Blacks. The limitations of the ratio, especially with regard to concomitant drug therapy will be discussed in detail. The fludrocortisone suppression test remains the investigation of choice for confirming the diagnosis, but requires four days of hospitalisation. CT scanning will miss 50% of adenomas and incorrectly lateralise the adenoma in occasional cases, and bilateral adrenal venous sampling is the gold standard for indirectly confirming and adenoma by demonstrating lateralisation of aldosterone secretion, but its use is limited by lack of technical expertise in South Africa. Low-dose spironolactone is the medical therapy of choice for PA.