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Test Name:
Tacrolimus, Whole Blood
- SBMF No:
30060 - Performance Lab Name:
Toxicology - Test Mnemonic:
TACROLIMUS - ABN:
Not required - CPT Code:
80197 - LOINC Code:
11253-2 - Also Known As:
FK506
Prograf®
Immunosuppressant - Spec Type:
Whole blood - Spec Container:
Lavender top (EDTA) tube - Pref Vol:
2.0 mL - Min Vol:
0.2 mL - Fasting:
No - Spec Collect:
Routine venipuncture - Spec Process:
Do not centrifuge
Do not remove plasma from cells - Spec Store Transport:
Refrigerated - Spec Stability:
2 weeks refrigerated (2-8°C)
1 month frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles - Methodology:
Liquid Chromatography/Tanden Mass Spectrometry (LC/MS.MS) - Use:
Monitor concentrations of tacrolimus primarily to prevent nephrotoxicity - Clinical Significance:
Tacrolimus is an immunosuppressive drug discovered in 1984 by the Fujisawa Pharmaceutical Co., Ltd. It has been shown to be effective for the treatment of rejection following transplantation. The results of clinical trials with liver and kidney have been published and clinical studies are continuing for a variety of indications.The mode of action for tacrolimus is under active investigation. Tacrolimus binds a family of proteins termed FK506 binding proteins (FKBP’s). The formation of a larger pentameric complex comprised of FKBP, tacrolimus, calmodulin and calcineurins A and B results in the inhibition of the phosphatase activity of calcineurin. The action of transcription factors requiring dephosphorylation for transport to the cell nucleus is thus inhibited leading to blockage of T-cell proliferation and function.
Pharpacokinetic studies with tacrolimus have shown that there are large inter- and intra-individual differences in its kinetics in organ transplant patients. Studies have also indicated that whole blood rather than plasma may serve as the more appropriate medium to describe the pharmacokinetic characteristics of tacrolimus. Tacrolimus is bound to proteins, mainly albumins, and alpha-1-acid glycoprotein, and is highly bound to erythrocytes.
Tacrolimus is extensively metabolized in the liver and small intestine microsomes utilizing the hepatic cytochrome enzymes. Nine different metabolites of tacrolimus have been identified; several of the metabolites have been found and tested in whole blood. At the present time it is not clear whether the nephrotoxicity of tacrolimus is the result of parent drug, metabolites, or a combination of both. The use of tacrolimus is associated with serious toxic side effects, primarily nephrotoxicity. Other adverse side effects include neurotoxicity, hypertension, insomnia and nausea. - Reference Range:
The therapeutic range of tacrolimus has not been fully established.
Monitoring drug concentration is recommended because studies have shown that increasing adverse effect with increasing trough blood concentration of the drug. Most of patients are stable when trough blood concentrations are maintained between 5 to 20 ng/mL at initiation of therapy. Long term post transplant patients are often maintained at approximately 5 ng/mL. - Critical High Value:
≥ 25.0 ug/mL - Additional Test Info:
The therapeutic range of tacrolimus has not been fully established. Monitoring drug concentration is recommended because studies have shown that increasing adverse effect with increasing trough blood concentration of the drug. Most of patients are stable when trough blood concentrations are maintained between 5 to 20 ng/mL at initiation of therapy. Long term post transplant patients are often maintained at approximately 5 ng/mL.
Limitations of Procedure:
This immunoassay is nonspecific and cross-reacts with Tacrolimus metabolites. When elimination of tacrolimus is impaired, Tacrolimus metabolites may accumulate. The immunoassay may overestimate the concentration of Tacrolimus. In such cases, the use of a specific assay (HPLC, GC/MS) could be considered. - Day Run:
Mon-Fri - Time Reported:
Next day - Test Type:
TOX-TDM
