The true prevalence of primary hyperaldosteronism is controversial. For many years, it was considered to be a rare disease but, more recently, studies have suggested that it affects approximately 10% of hypertensive patients. It is generally thought to be most prevalent among patients with resistant hypertension.

In this retrospective study, Douma et al. identified 1616 patients with confirmed resistant hypertension (BP > 140/90 mmHg despite a three drug regimen, including a diuretic) who had attended their outpatient clinic over the past 20 years. Three hundred and thirty-eight had a positive screening test, i.e. a high aldosterone to renin activity ratio (ARR) (>65.16) and a serum aldosterone concentration >416 pmol/L. Among these, further testing using a salt suppression test and response to spironolactone treatment lead to a final diagnosis of primary hyperaldosteronism in 182 patients (11.3% of the total study population). A comparison of these patients with 156 matched patients with essential hypertension revealed that systolic (SBP) and diastolic blood pressures (DBP) and the frequency of hypokalaemia were significantly higher in those with primary hyperaldosteronism compared to those with essential hypertension (SBP 182 mmHg vs. 165 mmHg; DBP 111 mmHg vs. 101 mmHg; percentage hypokalaemic 45.6% vs. 15.9%, respectively).

This study highlighted that ARR has a low positive-predictive value; only 53.8% of patients with a positive ARR were eventually diagnosed with primary hyperaldosteronism. There clearly needs to be a more reliable screening test in order to reduce the number of further unnecessary tests. Another notable observation was the low frequency of hypokalaemia indicating that the presence of hypokalaemia is not essential to diagnose primary hyperaldosteronism. Douma et al. suggest that primary hyperaldosteronism is less common than has until recently been considered and is over-represented in patients with resistant hypertension. Its higher prevalence in other studies (14–23%) could be attributed to selected populations in tertiary centres. Further studies in unselected populations are required in order to confidently estimate its true prevalence.