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.
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.
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.
CLIA values should be carefully interpreted in RA patients, especially those receiving a low dose of tacrolimus.