DOSAGGIO DIRETTO DELLA RENINA CON METODICA CHEMILUMINOMETRICA:CONFRONTO CON LA TECNICA ENZIMATICA ED UTILIZZO NELLO SCREENINGDELL¿IPERALDOSTERONISMO PRIMITIVO

Background: Direct plasma renin concentration determined with chemiluminometric immunoassay (CliR, mU/l) is progressively replacing plasma renin activity (PRA, ng/ml/h) for clinical use but the conversion factors (CF) between the two methods are still unsettled as well as their influence on the calculation of aldosterone/renin ratio (ARRD and ARRP). Methods: CliR, PRA and aldosterone (A, ng/dl) were measured in plasma samples collected in the supine position (S) and after 1 hour of active standing (AS) in 88 patients with essential hypertension (EH) on treatment with various antihypertensive drugs including ACEIs and ARBs. The same determinations were made in S in 10 patients with primary hyperaldosteronism (PHA) due to adrenal adenoma histologically confirmed. Results: In EH the median values (range) of CliR in S and AS were 18 (2-255) and 28 (4-471) respectively, the corresponding values of PRA being 0.6 (0.2-11.2) and 1.3 (0.3-16.0). Supine and upright CliR and PRA were highly correlated with a Spearman rs of 0.85 and 0.84 respectively. The linear non parametric Passing-Bablok regression on all logarithmic values in S and AS gave a slope of 1.01, an intercept of 3.2 and a CF of 24.6 between PRA and CliR on the natural scale. In EH the median values (range) of A in S and AS were 7.8 (0.3-31) and 18.4 (2.3-60). In PHA patients the median values of CliR, PRA and A in S were 0.8 (0.2-10.2), 0.1 (0.1-0.6) and 36.8 (11.8-122). In EH the median values of ARRD in S and AS were 0.4 (0.01-3) and 0.5 (0.02-7.8) respectively, the corresponding values of ARRP being 12 (0-71) and 13 (0-80). ARRD and ARRP were strongly correlated, with an rs of 0.88 and 0.92 in S and AS respectively. The regression analysis of all logarithmic values in S and AS showed a slope of 1.12, an intercept of -3.53 and a CF of 0.03 between ARRP and ARRD on the natural scale. In PHA patients the median value of ARRD in S was 34 (2.8-244) and that of ARRP 298 (48-1222). Assuming as cut-off values of normalcy those recommended by guidelines (Funder et al, JCEM 2008; 93: 3266) i.e. 30 for ARRP and 3.7 for ARRD, there were 13 false positives in S and 18 in AS for ARRP with a specificity of 0.85 (CI95% 0.76-0.92) and of 0.78 (0.68-0.87) respectively while with ARRD there were only 0 and 4 false positives with a specificity of 1 (0.96-1) and of 0.95 (0.88-0.99). Conclusions: In EH on treatment CliR and PRA, as well as ARRD and ARRP, are highly correlated. However, using the conventional cut-off values, for the diagnosis of PHA the specificity of ARRD is better than that of ARRP. Moreover the specificity of ARRD appears to be minimally affected by antihypertensive treatment.