Brief Cryoactivation Markedly Affects Plasma Renin Activity and Direct Renin Measurement in Low Renin Samples: Pp.24.473

Background: Exposure of plasma to low temperature (0°-4°C) i.e. cryoactivation (C) is known to increase plasma renin activity (PRA, ng/ml/h) but it is not known to what extent C affects the measurement of immunoreactive renin (IR, mU/L) measured with the direct renin assays (DRA) in plasmas with different renin content. Methods: Aliquots of human pool plasmas with low (L), intermediate (I) and high (H) renin were exposed to C for 0, 24, 48, 72 and 96 hours (hrs) and then measured in triplicate as PRA with the conventional enzymatic method and as IR with a new chemiluminescent DRA (Dia-Sorin LIAISON). Results: In L samples PRA rose from 0.14 ± 0.01at baseline to 0.53 ± 0.01(+ 270%) and to 1.1 ± 0.03 (+ 680%) respectively after 24 and 96 hrs of C whereas at the corresponding times IR rose from a baseline of 4.1 ± 0.1 to 11.3 ± 0.4 (+ 174%) and to 24.6 ± 0.4 (+ 595%). In I samples, for the same hrs of C, PRA rose from 1.9 ± 0.02 to 2.3 ± 0.04 (+ 17%) and to 4.1 ± 0.05 (+ 110%), whereas IR rose from 48.7 ± 0.3 to 61.7 ± 0.9 (+ 27%) and to 118 ± 3 (+ 142%). In H samples PRA rose from 7.8 ± 0.2 at baseline to 8.7 ± 0.2 (+ 11%) and to 10.5 ± 0.6 (+ 34%) whereas IR rose from 222 ± 2 to 241 ± 2 (8%) and to 289 ± 2 (+ 30%). The increments of PRA and IR were always statistically significant with respect to baseline values and, in percent, similar with the two assays. Conclusions: Thus C affects the measurement of renin to the same extent with the two assays, but the percent increases in PRA and IR are particularly relevant in L samples. In these cases even short period of inadvertent C can lead to an overestimation of the true renin levels.