title: A liquid chromatography tandem mass spectrometry assay for plasma renin activity using online solid-phase extraction.
abstract: BACKGROUND
  The plasma renin activity (PRA) assay measures the ability of renin to generate angiotensin I (AngI) from angiotensinogen. It is used to monitor mineralocorticoid therapy and to screen hypertensive individuals for primary aldosteronism (PA).
  
  
  METHODS
  Samples were incubated in the presence of protease inhibitors for 6.5 and 24 h. The reaction was stopped by the addition of 2% ammonium hydroxide. AngI was then quantified by liquid chromatography tandem mass spectrometry using online solid-phase extraction (XLC-MS/MS).
  
  
  RESULTS
  This method requires a sample volume of 50 μL and has an inter-assay precision <14% across the working range. A 6.5-h incubation gave a lower limit of quantification (LLOQ) of 0.3 nmol/L/h and this can be reduced to 0.08 nmol/L/h using a 24-h incubation. Comparison to a radioimmunoassay revealed excellent correlation (r(2) = 0.98), but a 37% negative bias. We also found that renin is stable in whole blood for up to 24 h at room temperature. In contrast, storage at 4°C should be avoided as prorenin cryoactivation can affect the PRA result in some patient groups.
  
  
  CONCLUSIONS
  We have developed and fully validated a semi-automated XLC-MS/MS method for the measurement of PRA. In addition, a reference range specific to this assay has been defined. We have also demonstrated that renin is stable for up to 24 h at room temperature. This will enable this assay to be extended to samples taken in primary care, potentially increasing the number of hypertensive patients who can be screened for PA.
authors.affiliation: Department of Clinical Biochemistry, University Hospital of South Manchester, Southmoor Road, Manchester M23 9LT, UK.
authors.forename: S
authors.initials: S
authors.lastname: Carter
authors.forename: L J
authors.initials: LJ
authors.lastname: Owen
authors.forename: M N
authors.initials: MN
authors.lastname: Kerstens
authors.forename: R P F
authors.initials: RP
authors.lastname: Dullaart
authors.forename: B G
authors.initials: BG
authors.lastname: Keevil
mesh_terms: D000803:Angiotensin I / Q000097:blood; D001774:Blood Chemical Analysis / Q000379:methods*; D002853:Chromatography, Liquid; D012015:Reference Standards; D012083:Renin / Q000097:blood* / Q000378:metabolism; D052616:Solid Phase Extraction; D053719:Tandem Mass Spectrometry
chemical_list: D000803:Angiotensin I; D012083:Renin