Aldosterone to active Renin ratio as screening test for primary aldosteronism: reproducibility and influence of orthostasis and salt loading.

Measurement of the aldosterone to active renin ratio (AARR) is the recommended screening test for primary aldosteronism (PA), but several sampling conditions impact on the AARR. We aimed to evaluate the reproducibility and the influence of orthostasis and salt loading on the AARR. The Graz Endocrine Causes of Hypertension (GECOH) study is a diagnostic accuracy study among hypertensive patients at a tertiary care centre in Graz, Austria. With a median interval of 4 weeks we determined the AARR under standardized sampling conditions twice in the sitting position, after 1h in the supine position, and after a salt infusion test (SIT). We identified 9 patients with PA and 151 patients with essential hypertension (EH). The Pearson correlation coefficient between both AARR measurements in the sitting position was 0.79 (p<0.001). In EH, recumbency was associated with a significant decrease of aldosterone and, to a lesser extent, of renin, thus lowering the AARR as compared to the sitting position (p<0.001 for all). In PA, recumbency had only minor effects, but it increased the rate of false negative AARR. SIT suppressed the AARR and its components in EH, whereas in PA only renin was slightly decreased. AARR has a good intra-individual reproducibility and decreases during recumbency. These results suggest that a single AARR determination in the sitting position is a reliable screening tool for PA.