title: Pre-analytical and analytical considerations for the determination of plasma renin activity.
abstract: 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.
authors.affiliation: Department of Nuclear Medicine, University Hospital and University of Bordeaux, France. julie.brossaud@u-bordeaux2.fr
authors.forename: Julie
authors.initials: J
authors.lastname: Brossaud
authors.forename: Jean-Benoît
authors.initials: JB
authors.lastname: Corcuff
mesh_terms: 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
chemical_list: D004798:Enzymes; D011933:Reagent Kits, Diagnostic; D000803:Angiotensin I; D012083:Renin