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The impact of a change in tacrolimus monitoring immunoassay techniques on clinical decision making.

CONTEXT
Tacrolimus is an immunosuppressant that undergoes therapeutic drug monitoring. The laboratory at our institution changed its immunoassay techniques from the fluorescence polarization immunoassay to the cloned enzyme donation immunoassay.


OBJECTIVE
To evaluate the relationship between the 2 assays and to determine the impact of the change on clinical decision making.


DESIGN
A retrospective study of patients admitted to the hospital during the assay transition period. Tacrolimus values for the 2 assays were collected for 4 weeks and compared.


SETTING
An academic health center.


PATIENTS
Liver transplant patients hospitalized from February 18, 2008, to March 18, 2008.


MAIN OUTCOME MEASURE
The primary outcome was the agreement between the results of the 2 immunoassays. Secondary outcome was agreement of clinical decision making with established patient-specific therapeutic ranges or with a 30% difference in absolute values between the assays.


RESULTS
Seventy-nine pairs of tacrolimus concentrations were collected from 21 liver transplant patients. The mean (SD) tacrolimus concentrations were 7.36 (4.21) microg/L for the fluorescence polarization immunoassay and 9.00 (5.30) microg/L for the cloned enzyme donation immunoassay (P = .03). A clinically different decision would have been made if the fluorescence polarization immunoassay value had not been reported 51% of the time. A Bland-Altman plot indicated no relationship between the assay results.


CONCLUSION
A change in tacrolimus monitoring assay would have resulted in different clinical decisions 51% of the time. Awareness of changes in assay technology must be heightened to enhance clinical decision making and prevent potential impact on morbidity among liver transplant patients.