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Test Code MISC Tacrolimus, Peak, Blood

Important Note

Mayo code TACPK

Useful For

Assessment of postdosing (peak) blood tacrolimus concentrations

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reporting Name

Tacrolimus, Peak, B

Specimen Type

Whole Blood EDTA

Necessary Information

Date of last dose, time of last dose, and dosage information are required.

Specimen Required

Container/Tube: Lavender top (EDTA)

Specimen Volume: 3 mL

Collection Instructions: 

1. Do not centrifuge.

2. Send specimen in original tube.

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole Blood EDTA Refrigerated (preferred) 14 days
  Ambient  14 days
  Frozen  14 days

Reject Due To

Gross hemolysis OK
Gros lipemia OK
Gross icterus OK

Clinical Information

Tacrolimus (Prograf) is a macrolide antibiotic derived from the fungus Streptomyces tsukubaenesis. Like cyclosporine, tacrolimus inhibits calcineurin to suppress T cells. Tacrolimus is metabolized by CYP3A4; thus, its concentration is affected by drugs that inhibit (calcium channel blockers, antifungal agents, some antibiotics, grapefruit juice) or induce (anticonvulsants, rifampin) this enzyme. Tacrolimus has a narrow therapeutic range and adverse effects are common, particularly at high dose and concentrations, making therapeutic drug monitoring essential.


Since 90% of tacrolimus is in the cellular components of blood, especially erythrocytes, whole blood is the preferred specimen for analysis of trough concentrations. Target steady-state concentrations vary depending on clinical protocol, the presence or risk of rejection, time from transplant, type of allograft, concomitant immunosuppression, and side effects (mainly nephrotoxicity). Optimal trough blood concentrations are generally between 5.0 and 15.0 ng/mL. Higher levels are often sought immediately after transplant, but as organ function stabilizes at about 4 weeks from transplant, doses are generally reduced in solid organ transplant patients who are stable. Trough concentrations should be maintained below 20 ng/mL.


Optimal postdose sampling strategies and blood concentrations have not been well established for tacrolimus. A study of 54 liver transplant patients suggested that most individuals have tacrolimus blood concentrations ranging between 5.0 and 30.0 ng/mL in samples drawn 1 to 4 hours after dosing, although some patients showed slightly higher blood concentrations at 1-hour postdose.

Reference Values

5.0-30.0 ng/mL


Target steady-state trough concentrations vary depending on the type of transplant, concomitant immunosuppression, clinical/institutional protocols, and time posttransplant. Results should be interpreted in conjunction with this clinical information and any physical signs or symptoms of rejection or toxicity.

Day(s) and Time(s) Performed

Monday through Friday; Continuous until 3 p.m.

Saturday, Sunday; Continuous until 1 p.m.

Analytic Time

Same day/1 day

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
TACPK Tacrolimus, Peak, B 59822-7


Result ID Test Result Name Result LOINC Value
88157 Tacrolimus, Peak, B 59822-7
DAT7 Date of last dose 29742-4
TM01 Time of last dose 29637-6
DOSE1 Dose, mg 32594-4

NY State Approved



If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.