【Objective】Tacrolimus is a potent immunosuppressive drug. But because of its narrow therapeutic range, the monitoring of blood level is necessary. Various methods of measurement are available. We evaluated two immunoassay methods: affinity column mediated immunoassay (ACMIA) and chemiluminescent enzyme immunoassay (CLIA) using identical blood samples.
【Methods】We tested 2074 blood samples obtained from 196 patients from June 2010 to February 2012. The mean age of patients was 58.9 (range 22.5-88.9) years. Primary diseases included rheumatism, lupus nephritis, inflammatory bowel disease, polymyositis, dermatomyositis and myasthenia gravis. Treatments included hematopoietic stem-cell transplantation, renal transplantation and liver transplantation. ACMIA and CLIA were carried out according to manufacturer instructions using Dimension™ Xpand-HM and ARCHITECT™ i1000SR, respectively.
【Results】Mean blood concentrations of tacrolimus (in ng/mL) were 6.0 (ACMIA) and 7.2 (CLIA), and this difference was significant (p＜0.01). Excellent linear correlation (R2 = 0.92) was observed, but the blood concentration measured by ACMIA was 19% lower than that obtained by CLIA for all samples. At low concentrations of CLIA (＜5 ng/mL), the discrepancy was more than 40%.
【Conclusion】Tacrolimus concentration in blood as measured by ACMIA was significantly lower than that measured by CLIA. It is clinically important to understand the characteristics of the two methods.