Multicenter comparison of tacrolimus (FK) 506 whole blood concentrations as measured by the abbott imx analyzer and enzyme immunoassay with methylene chloride extraction

A multicenter comparison was made between the Abbott IMX and enzyme-linked immunosorbent assay (ELISA) procedures for analysis of tacrolimus (FK 506) in whole blood. Proficiency samples and 853 patient specimens obtained after various organ transplantations were assayed by 13 laboratories. Both groups of test samples yielded slightly lower (7 and 13) values by the IMX method, but the difference is not clinically meaningful. The type of organ transplant was not a factor that contributed to assay variation. The Abbott IMX results were essentially equivalent to ELISA and considerably facilitates monitoring of FK 506 therapy.