The effect of blood collection procedure on plasma renin activity (PRA) and concentrations of direct renin (DRC) and aldosterone

Introduction: Performing measurements of plasma renin activity (PRA) or direct renin concentration (DRC) and aldosterone concentration, we should be well informed about requirements concerning blood sample processing. Material and methods: Forty-seven patients had blood collected in the supine and upright positions. Blood was withdrawn into two EDTA 2 K tubes and one with clot activator. One EDTA 2 K tube was cooled at +4°C and centrifuged at +4°C whereas the other was prepared at room temperature. PRA and DRC were measured by radioimmunoassay (RIA) and radioimmunometry (IRMA), respectively, in both cooled and not cooled plasma samples, and aldosterone was measured by RIA in not cooled plasma and in serum. Results: In all the groups, with low, medium, and high values of PRA and direct renin, the temperature of sample processing within 30 minutes had no marked influence on the final result (correlation coefficient for renin was 0.9994, and for PRA, 0.8297). The measured concentrations of aldosterone also showed high correlation (r = 0.9790) but were markedly higher in plasma. Conclusion: The measurements of DRC, and to a lesser extent PRA, were similar regardless of temperature condition during the 20-30 minutes necessary for blood sample processing. Aldosterone concentrations in plasma vs serum samples appeared to be markedly higher.