title: Suitability of chemiluminescent enzyme immunoassay for the measurement of blood tacrolimus concentrations in rheumatoid arthritis.
abstract: OBJECTIVE
  The aim of this study was to evaluate the suitability of chemiluminescent enzyme immunoassay (CLIA) for the monitoring of whole-blood tacrolimus concentrations in rheumatoid arthritis (RA) patients.
  
  
  METHODS
  Sixty-three RA patients and 47 renal transplant (RT) patients treated with tacrolimus were enrolled. Tacrolimus concentrations in spiked blood and patient blood were measured by CLIA and HPLC-MS/MS. The cross-reactivity in CLIA was evaluated using 13-O-demethylated or 31-O-demethylated tacrolimus.
  
  
  RESULTS
  Tacrolimus concentrations measured by CLIA correlated with those measured by HPLC-MS/MS. Bland-Altman analysis revealed the 95% confidence intervals between CLIA and HPLC-MS/MS in RA and RT patients were -20.7 to 109.9% and -5.0 to 74.1%, respectively. While 31-O-demethylated tacrolimus cross-reaction amounted to an equivalent of 120% tacrolimus in CLIA, 13-O-demethylated tacrolimus did not cross-react.
  
  
  CONCLUSIONS
  CLIA values should be carefully interpreted in RA patients, especially those receiving a low dose of tacrolimus.
authors.affiliation: Department of Hospital Pharmacy, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu, Shizuoka 431-3192, Japan.
authors.forename: Kumi
authors.initials: K
authors.lastname: Hirano
authors.forename: Shuji
authors.initials: S
authors.lastname: Maruyama
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Mino
authors.forename: Takafumi
authors.initials: T
authors.lastname: Naito
authors.forename: Junichi
authors.initials: J
authors.lastname: Kawakami
mesh_terms: D001172:Arthritis, Rheumatoid / Q000097:blood*; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods*; D007166:Immunosuppressive Agents / Q000097:blood*; D049449:Luminescence; D015203:Reproducibility of Results; D016559:Tacrolimus / Q000097:blood*; D053719:Tandem Mass Spectrometry
chemical_list: D007166:Immunosuppressive Agents; D016559:Tacrolimus