The objective of the study was to assess whether the calculated ratio of plasma aldosterone concentration (PAC) to renin activity (PRA) removes variation in PAC attributable to differences in PRA making ARR independent of PRA. Population-based samples of 149 black and 180 white subjects, ages 30–60 years, with essential hypertension were recruited. All antihypertensive drugs were stopped for at least 4 weeks; then hydrochlorothiazide was given for 4 weeks. PAC and PRA were measured at the end of the drug-free period (baseline) in the supine and upright postures, and after diuretic therapy. Inter-individual differences in PRA: In each race-gender group, the ARR was significantly and inversely related to PRA both in the supine and upright postures and after diuretic therapy; in some race-gender groups, the ARR demonstrated greater interindividual variation than PAC. Intra-individual differences in PRA: In each race-gender group, the change from supine to upright was associated with a disproportionately greater increase in PAC than in PRA, causing the ARR to increase. In contrast, diuretic therapy was associated with a disproportionately greater increase in PRA than in PAC, causing the ARR to decrease. The ARR inappropriately adjusts PAC for PRA and does not allow unbiased comparisons among or within individuals with different PRA.
