Difference in blood tacrolimus concentration between ACMIA and MEIA in samples with low haematocrit values.

OBJECTIVES: The aim was to compare blood tacrolimus concentrations in anaemic patients between affinity column-mediated immunoassay (ACMIA) and microparticle enzyme immunoassay (MEIA). METHODS: Blood concentrations of tacrolimus in 235 whole-blood samples from 64 patients treated with tacrolimus were determined by the two assay methods. Fifty-three samples had low haematocrit (Ht) values (<25%), whereas the other samples had normal Ht values. KEY FINDINGS: Measured tacrolimus concentrations in samples with normal Ht values did not differ between ACMIA and MEIA (median, range; 6.6, 0-29.1 vs 7.3, 0-27.4 ng/ml). On the other hand, MEIA determined significantly higher tacrolimus concentrations in samples with lower Ht values compared with ACMIA (14.0, 2.4-25.7 vs 11.5, 0-21.3 ng/ml; P < 0.05). This difference was caused by overestimated blood concentrations in MEIA derived from lower Ht values, which could be corrected using the Ht value for each sample (calculated MEIA (MEIAcalc)). The corrected concentrations (MEIAcalc; 10.8, 0-21.3 ng/ml) were comparable with those of ACMIA. It was confirmed that the difference in concentrations between ACMIA and MEIA was remarkable in routine monitoring of blood tacrolimus for a liver transplant recipient with anaemia. CONCLUSIONS: ACMIA can be applied to routine therapeutic drug monitoring of tacrolimus therapy in anaemic patients.