Therapeutic drug monitoring is necessary when using tacrolimus (FK) due to the associated side effects. The aim of this study was to compare the chemiluminescent assay (CMIA) system with the previously established Abbott IMx Tacrolimus II microparticle enzyme immunoassay (MEIA) in liver transplant recipients and evaluate its accuracy. Between March and June 2008, all blood samples from the liver transplant recipients at the hospital were tested for FK trough level using 2 different methods, CMIA and MEIA. The post-transplant time, hematocrit, and other clinical parameters during the study period were recorded. FK trough level was analyzed in 398 samples from 57 liver transplant recipients by CMIA and MEIA. The correlation in FK level between the 2 methods was excellent (r2 = 0.941). However, the FK level was underestimated in MEIA by more than 23% in samples with an FK level of less than 3.5 ng/mL and by 6.8% in those with an FK level between 3.5 and 5 ng/mL. CMIA is superior to MEIA in measuring low FK level, allowing the FK level to be maintained at less than 5 ng/mL in selected liver transplant recipients. The effects of maintaining low levels of FK should be evaluated in liver transplant recipients.
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