Direct Versus Enzymatic Renin Measurement for the Calculation of Aldosterone / Renin Ratio in Patients with Essential Hypertension and with Primary Hyperaldosteronism

Background. A new chemiluminescent immuno assay (CLIA) has been recently developed, as an alternative to the enzymatic method, for the direct quantification of plasma renin (R). Methods. We aimed at comparing the aldosterone/renin ratios with R measured as plasma renin activity (ng/ml/h) or as plasma renin concentration (mU/dl), respectively ARRE and ARRD, in plasma samples collected in the supine position (S) and after 1 hour of active standing (AS) in 42 patients with essential hypertension (EH) off treatment with angiotensin converting enzyme inhibitors (ACEI) or angiotensin receptor antagonists (ARA), in 35 EH on treatment with these medications and in 8 patients off treatment with primary hyperaldosteronism (PHA) due to adrenal adenoma. Results: In the 42 EH not on treatment with ACEI/ARA ARRE was 17.7 ± 1.7 (range 1.1-47) in S and rose to 20.7 ± 2.4 (range 2.5-58.4) after AS, the corresponding values of ARRD being 5.2 ± 1.0 (range 0.5-30.3) and 6.8 ± 1.3 (range 1.1-33.6). In the 35 EH on treatment with ACEI/ARA, ARRE was 10.6 ± 1.8 (range 0.4-39.5) in S and rose to 13.6 ± 2.8 (range 0.4-69.7) after AS, the corresponding values of ARRD being 1.8 ± 0.9 (range 0.1-27.3) and 2.4 ±2.5 (range 0.1-77.5). The standing induced changes in ARRE and ARRD were not significantly different with respect to S whereas both in S and after AS ARRE and ARRD were higher in EH not on treatment with ACEI/ARA (p< 0.001). In patients with PHA, ARRE was 336 ± 101 (range 33-857) in S and 343 ± 108 (range 11-850) after AS, the corresponding values of ARRD being 304 ± 107 (range 30-779) and 271 ± 97 (range 17- 686). In these patients ARRE and ARRD were similar in S and after AS but in both positions were higher than in patients with EH treated or not treated with ACEI/ARA (p< 0.001). Conclusions: These data provide the reference limits of ARRD in EH, both on and off treatment with ACEI/ARA, and show that the calculation of ARR with the new CLIA direct method can be a valid alternative to that of ARRE for detecting PHA. Moreover in PHA, as well as in EH, ARRE and ARRD are unchanged after AS, whereas in EH are significantly reduced by treatment with ACEI/ARA.