When diagnosing primary
aldosteronism, the measurement of urinary
aldosterone after oral
sodium loading is one of the currently recommended confirmatory tests. The aim of the study was to assess the repeatability and interpretation of urinary
aldosterone in patients examined for suspected primary
aldosteronism. Sixty-four hypertensive patients with suspected primary
aldosteronism were prospectively enrolled and examined according to the study protocol. After
antihypertensive medications interfering with renin-angiotensin-aldosterone system were withdrawn for at least 2 weeks, the confirmatory testing was performed: oral
sodium loading preceded the collection of 24-h urine sample and subsequent saline infusion test. The identical procedures were repeated after 2 weeks. The concordant results of both saline infusion tests served for confirmation/exclusion of primary
aldosteronism. Forty-nine patients were included in data analysis. Primary
aldosteronism was excluded in 16, and confirmed in 33 individuals. The repeatability of urinary
aldosterone was evaluated in 44 patients: the difference of urinary
aldosterone levels ranged between 1 and 88% (median 31%). Ninety-three urine samples from 49 patients were used to validate the interpretation of urinary
aldosterone in respect to the diagnosis of primary
aldosteronism made by saline infusion testing; 96% sensitivity was characterized by urinary
aldosterone ≥19 nmol/day, and 96% specificity was associated with urinary
aldosterone ≥92 nmol/day. In 22 (45%) patients, urinary
aldosterone remained in the "gray" zone between 19 and 92 nmol/day in all provided samples. The estimation of urinary
aldosterone excretion after oral
sodium loading is associated with marked intraindividual variability, and significant number of inconclusive results.