title: Two suspected cases of immunoglobulin-mediated interference causing falsely low vancomycin concentrations with the Beckman PETINIA method.
abstract: OBJECTIVE
  To describe 2 recent cases of suspected immunoglobulin-mediated interference with the Beckman Coulter particle-enhanced turbidimetric inhibition immunoassay (PETINIA) used to measure vancomycin serum or plasma concentrations and to review the existing literature.
  
  
  METHODS
  A 64-year-old woman with a history of multiple immune-related comorbidities received vancomycin for treatment of a prosthetic joint infection growing coagulase-negative Staphylococcus spp. A 33-year-old man with a history of Felty syndrome received vancomycin for the treatment of methicillin-resistant Staphylococcus aureus pneumonia. Both patients had multiple vancomycin trough concentrations determined using the Beckman Coulter PETINIA method and had measured concentrations reported as less than 4 mg/L despite appropriate vancomycin dosing for their size, age, and organ function. The patients' serum was then tested by alternative methods, which reported vancomycin concentrations consistent with those expected with the patients' dosing regimens.
  
  
  CONCLUSIONS
  Immunoglobulins are well known for interfering with chemistry assays. It is suspected that high levels of immunoglobulins in these 2 patients interfered with the accurate measurement of serum vancomycin concentrations. An objective causality assessment supported the interactions as being definite and probable, respectively. Two other cases of suspected immunoglobulin interference with vancomycin measurement have been reported in the literature when vancomycin concentrations were initially measured using the Beckman Coulter PETINIA method. In vitro studies support the hypothesis that immunoglobulin interference with vancomycin measurement by this method occurs and is a graded phenomenon.
  
  
  CONCLUSIONS
  These cases suggest a high likelihood of immunoglobulin-mediated interference with the Beckman Coulter PETINIA method, which results in the reporting of falsely low vancomycin serum concentrations. When vancomycin concentrations do not correlate with what would be expected clinically, clinicians should have a high index of suspicion for potential assay interference.
authors.affiliation: Pharmacy Services, University of Alberta Hospital, Edmonton, Alberta, Canada. mary.gunther@albertahealthservices.ca
authors.forename: Mary
authors.initials: M
authors.lastname: Gunther
authors.forename: Lynora
authors.initials: L
authors.lastname: Saxinger
authors.forename: Margaret
authors.initials: M
authors.lastname: Gray
authors.forename: Donald
authors.initials: D
authors.lastname: Legatt
mesh_terms: D000328:Adult; D000900:Anti-Bacterial Agents / Q000097:blood; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007136:Immunoglobulins / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D014640:Vancomycin / Q000097:blood*
chemical_list: D000900:Anti-Bacterial Agents; D007136:Immunoglobulins; D014640:Vancomycin