title: The effect of paraproteins and rheumatoid factor on four commercial immunoassays for vancomycin:  implications for laboratorians and other health care professionals.
abstract: BACKGROUND
  Paraproteins, immunoglobulins (Igs), which are elevated in various autoimmune disorders, are known to interfere with various laboratory immunoassays, including vancomycin (VANC). Rheumatoid factor (RF), a known immunoassay interferant, may cause falsely elevated results.
  
  
  OBJECTIVE
  The aims of this study were to (1) evaluate the effect of 3 paraproteins (IgA, IgG, and IgM) on 4 commercial VANC immunoassays [fluorescence polarization immunoassay; enzyme multiplied immunoassay; 2 particle-enhanced turbidimetric inhibition immunoassays]; (2) determine the concentration at which the effect is obtained, and (3) examine the influence of RF on the VANC methods.
  
  
  METHODS
  Serum and plasma pools from patients prescribed VANC and a spiked VANC pool (20 mg/L) were each mixed 1:1 with individual patient specimens containing IgA (6-63 g/L), IgG (6-54 g/L), IgM (3-30 g/L) (n = 4 for each Ig), and a patient RF pool (196 IU/L). The mixtures (n = 39) were split and distributed for VANC analysis.
  
  
  RESULTS
  IgA and IgG in serum and plasma did not affect any of the VANC immunoassays. RF added to plasma specimens did not interfere, but in serum, elevated VAN results were observed. IgM did not affect the fluorescence polarization immunoassay and enzyme multiplied immunoassay methods but did attenuate VANC concentrations by both particle-enhanced turbidimetric inhibition immunoassays (Siemens, Beckman Coulter), with a more pronounced effect on the latter, producing concentrations >20% lower than expected in the patient serum and spiked plasma pools. The effect was progressively negative at effective IgM concentrations of 10 and 15 mg/L.
  
  
  CONCLUSIONS
  This phenomenon is a major analytical and clinical issue that must be communicated to health care professionals caring for patients receiving VANC, so optimal therapy is achieved.
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Alberta Hospital, Canada. don.legatt@albertahealthservices.ca
authors.forename: Donald F
authors.initials: DF
authors.lastname: LeGatt
authors.forename: George B
authors.initials: GB
authors.lastname: Blakney
authors.forename: Trefor N
authors.initials: TN
authors.lastname: Higgins
authors.forename: Kareena L
authors.initials: KL
authors.lastname: Schnabl
authors.forename: Carol E
authors.initials: CE
authors.lastname: Shalapay
authors.forename: Valerian C
authors.initials: VC
authors.lastname: Dias
authors.forename: James C
authors.initials: JC
authors.lastname: Wesenberg
mesh_terms: D000900:Anti-Bacterial Agents / Q000097:blood*; D006282:Health Personnel / Q000592:standards; D006801:Humans; D007118:Immunoassay / Q000379:methods / Q000592:standards; D007070:Immunoglobulin A / Q000502:physiology; D007074:Immunoglobulin G / Q000502:physiology; D007075:Immunoglobulin M / Q000502:physiology; D017056:Medical Laboratory Personnel / Q000592:standards*; D010266:Paraproteins / Q000502:physiology*; D012217:Rheumatoid Factor / Q000502:physiology*; D014640:Vancomycin / Q000097:blood* / Q000592:standards
chemical_list: D000900:Anti-Bacterial Agents; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D010266:Paraproteins; D014640:Vancomycin; D012217:Rheumatoid Factor