Pre-analytical and analytical considerations for the determination of plasma renin activity.
BACKGROUND
Primary hyperaldosteronism diagnosis is helped by assaying renin concentrations either by immunodetection (active renin) or by enzymatic reaction followed by angiotensin I immunoassay (plasma renin activity). We investigated the impact of pre-analytical and analytical conditions on a PRA assay.


METHODS
PRA was assayed using a commercial kit. Firstly, a retrospective analysis of PRA results from 1yr was performed. Secondly, the impact of pre-analytical temperature conveyance/storage of samples was tested (4 and 25 degrees C). Thirdly, 2 durations of enzymatic reaction 1.5 and 18h were tested.


RESULTS
Retrospectively, 9.5% samples displayed elevated "blanks": calculating PRA with or without "blank" subtraction elicited a difference of >10% in 1/3 samples. There was a significant decrease of PRA values in samples left at 25 degrees C vs 4 degrees C (50% "blank" increase). Finally, the longer the enzymatic reaction (1.5 vs 18h), the higher the production of angiotensin I and the better the PRA assay sensitivity.


CONCLUSIONS
We propose a 2 step procedure: a brief 1.5h enzymatic reaction time followed by a prolonged reaction (18h) only if PRA is <0.2ng mL(-1) h(-1). We would recommend performing "blank" samples for the brief enzymatic reaction time. Finally, conveyance/storage temperature does modify PRA results albeit in our hands this had little clinical impact.
Brossaud
Julie
J
Department of Nuclear Medicine, University Hospital and University of Bordeaux, France. julie.brossaud@u-bordeaux2.fr
Corcuff
Jean-Benoît
JB
D000803:Angiotensin I; D004798:Enzymes; D006801:Humans; D006929:Hyperaldosteronism / Q000175:diagnosis; D008722:Methods; D011933:Reagent Kits, Diagnostic / Q000592:standards; D012083:Renin / Q000097:blood*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013696:Temperature; D013997:Time Factors
D004798:Enzymes; D011933:Reagent Kits, Diagnostic; D000803:Angiotensin I; D012083:Renin