Stability of direct renin concentration and plasma renin activity in EDTA whole blood and plasma at ambient and refrigerated temperatures from 0 to 72 hours.

Objectives: The aim of this study was to determine the appropriate transport and storage conditions for blood taken for direct renin concentration and plasma renin activity measurement, and whether cryoactivation of prorenin is seen at time points relevant to clinical practice.

Methods: Blood was extracted from n=10 volunteers into K-EDTA tubes. Stability of renin was assessed in whole blood stored at room temperature (15-25 °C) and in the refrigerator (2-8 °C) at 0 h, 8 h, and 24 h. The stability of renin in plasma was determined under the same conditions at 0 h, 24 h and 72 h.

Results: Stability of plasma renin activity and direct renin concentration in whole blood stored at room temperature was found to be acceptable for up to 24 h. At refrigerated temperature, whole blood stability was acceptable for measurement of direct renin concentration up to 8 h and plasma renin activity up to 24 h. In contrast, plasma renin activity was not stable in plasma stored at either room or refrigerated temperatures up to 24 h; however, direct renin concentration had acceptable stability in plasma stored at room temperature for up to 24 h, but stability was unacceptable at refrigerated temperatures.

Conclusions: Samples collected for plasma renin activity and direct renin concentration should be transported as whole blood to optimise stability. After sample processing, plasma can be kept at room temperature for up to 24 h for direct renin concentration, however, for determination of plasma renin activity separated plasma should be analysed or frozen as soon as possible.