title: A widely applicable plasma renin activity assay by LC-MS/MS with offline solid phase extraction.
abstract: BACKGROUND
  The measurement of plasma renin activity using LC-MS/MS is an attractive alternative to radioimmunoassay techniques. A published method for renin activity by LC-MS/MS uses equipment that is not available in all LC-MS/MS laboratories. Here, we present an offline modification to allow users of LC-MS/MS to perform this analysis without specialist equipment.
  
  
  METHODS
  Samples were prepared in duplicate and incubated for 6.5 h and 24 h. Solid phase extraction was performed offline using Waters Oasis MAX ion-exchange 96-well plate. A method comparison was performed between this assay and a previously published assay using on-line solid phase extraction.
  
  
  RESULTS
  The offline method for plasma rennin activity gave similar results to the on-line method across the concentration range. Analytical performance was also found to be comparable and the use of a 24 h incubation for low samples was also deemed unnecessary.
  
  
  CONCLUSIONS
  The method described is an acceptable alternative to a previously published assay which does not require the use of highly specialist equipment and will be applicable to the majority of LC-MS/MS users.
authors.affiliation: Biochemistry Department, University Hospital of South Manchester, Manchester, UK.
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Owen
authors.forename: Joanne
authors.initials: J
authors.lastname: Adaway
authors.forename: Karen
authors.initials: K
authors.lastname: Morris
authors.forename: Stephen
authors.initials: S
authors.lastname: Lockhart
authors.forename: Brian G
authors.initials: BG
authors.lastname: Keevil
mesh_terms: D001774:Blood Chemical Analysis / Q000379:methods*; D002853:Chromatography, Liquid; D006801:Humans; D012083:Renin / Q000097:blood* / Q000302:isolation & purification*; D052616:Solid Phase Extraction / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*; D013997:Time Factors
chemical_list: D012083:Renin
keywords: LC-MS/MS; Renin activity; solid phase extraction