Background: Determination of the aldosterone-to-renin ratio (ARR) in blood is the preferred screening test for primary aldosteronism. Renin can be measured as the plasma renin activity (PRA) or the plasma renin concentration (PRC). Consequently, the ARR can be measured either based on the PRA (ARR(pra)) or based on the PRC (ARR(prc)). In contrast with the ARR(pra), the data on reference values for the ARR(prc) are limited. Moreover, whether the ARR(pra) or ARR(prc) is affected by variations in salt intake is unknown.
Methods: We measured the PRA, the PRC, and serum aldosterone in 100 normotensive individuals between 20 and 70 years of age before and after a 3-day oral sodium-loading test (SLT). Participants were stratified according to age and sex. Data are presented as the median and interquartile range (IQR).
Results: Urinary sodium excretion after the SLT was ≥200 mmol/24 h in all participants. Serum aldosterone, PRA, and PRC values were significantly reduced after the SLT. PRC and PRA results were highly correlated [Spearman rank correlation r(s) = 0.80 and 0.74 before and after SLT, respectively; P < 0.001 for both]. The central 95% reference intervals for ARR(pra) before and after SLT were 0.07-1.45 h(-1) and 0.06-1.84 h(-1), respectively. The corresponding reference intervals for ARR(prc) were 4.1-81.3 pmol/ng and 3.9-74.8 pmol/ng. The median ARR(prc) decreased after the SLT from 19.5 pmol/ng (IQR, 13.0-29.4 pmol/ng) to 18.6 pmol/ng (IQR, 9.4-27.1 pmol/ng) (P = 0.005), whereas the median ARR(pra) did not change (P = 0.12). Both the ARR(prc) and ARR(pra) at baseline were higher in women than in men, whereas no sex difference was observed after sodium loading.
Conclusions: We present reference values for the ARR(prc) for healthy individuals. The ARR is affected to a variable degree by sex and sodium intake.