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Blood Test Tracker

Tacrolimus

The amount of the anti-rejection medicine tacrolimus in your blood just before your next dose, used by your transplant team to fine-tune treatment.

AI-verified against cited sources. Awaiting expert reviewAlso called TAC, FK506LOINC 11253-2

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What it is

Tacrolimus (brand names include Prograf, Envarsus XR and Astagraf XL) calms the immune system so the body is less likely to reject a transplanted organ. It is measured in whole blood rather than serum, because much of the drug is carried inside red blood cells. The sample is usually drawn right before your next dose, about 12 hours after the last dose of a twice-daily product, or about 24 hours after the last dose of a once-daily product. This is called a trough level.

Why it matters

Tacrolimus has a narrow window. Too little can leave a transplanted organ with less protection against rejection. Too much can strain the kidneys and nerves and can raise blood potassium and blood sugar. Levels differ a lot from person to person and change with other medicines, some foods, illness and the lab method. That is why transplant teams check them often, especially early after a transplant or after any change.

If it’s low

A level below your team's target means less tacrolimus in your blood than planned, which can mean less protection against rejection. Common explanations are a missed or late dose, a draw taken long after the last dose, or a medicine that speeds up tacrolimus breakdown. Your team will usually repeat the level and review how and when you take it.

Common causes

  • Missed or late doses
  • Blood drawn long after the last dose
  • Medicines that speed up tacrolimus breakdown, such as rifampin or rifabutin
  • Switching between tacrolimus products, such as twice-daily capsules and once-daily versions, which are not interchangeable milligram for milligram
  • Faster clearance in some people, so that the usual dose gives a lower level

What can help

  • Tell your transplant team about any missed or late doses
  • Ask whether the level should be repeated before anything is changed
  • Talk with your transplant team before making any change to your medicine

If it’s high

A level above your team's target means more tacrolimus in your blood than planned. It does not mean something is wrong by itself, and the cause is often simple, such as a blood draw taken soon after a dose. Higher levels are linked to a greater chance of kidney strain, tremor, headache, high potassium and high blood sugar, so your team will usually look at your kidney function and other labs along with the number.

Common causes

  • Blood drawn after taking the dose instead of before it
  • A recent dose increase
  • Medicines that slow tacrolimus breakdown, such as some antifungal medicines and macrolide antibiotics (for example ketoconazole, voriconazole or clarithromycin)
  • Grapefruit or grapefruit juice
  • Liver impairment, which slows clearance
  • Lab method differences (immunoassays can read higher than LC/MS/MS)

What can help

  • Confirm that your blood draw was timed before your dose, and note when you took your last dose
  • Ask your transplant team whether any medicine, supplement or food you have started could be raising your level
  • Talk with your transplant team before making any change to your medicine

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 5–20 ng/mL. Source: ARUP Laboratories, DailyMed, National Library of Medicine. Labs treat above 20 ng/mL as urgent.

What can affect your result

  • Time since your last dose, and which tacrolimus product you take (twice-daily or once-daily)
  • Lab method: immunoassay and LC/MS/MS results differ, so follow your trend within one lab and method
  • Medicines that strongly slow or speed up CYP3A4 and P-glycoprotein, and grapefruit juice
  • Liver function
  • Race and ancestry: FDA labeling notes African-American patients may need higher doses to reach comparable troughs
  • Time since transplant and the type of organ, which set the target range
  • Taking tacrolimus the same way every day relative to food, because food changes absorption
  • Drawing the sample after taking the dose, or long after the usual trough time, changes the result. Tell the lab when you took your last dose.
  • Immunoassays can react with tacrolimus breakdown products and read higher than LC/MS/MS, and the size of the difference depends on the assay and the lab (FDA labeling).
  • Use an EDTA (lavender-top) tube. FDA labeling advises against heparin tubes because the blood tends to clot in storage.
  • Levels in people receiving tacrolimus as a continuous IV infusion are not comparable with the oral trough ranges.
  • Grapefruit and many medicines (strong CYP3A inhibitors and inducers) change tacrolimus levels in the body.

Just before your next dose: about 12 hours after the last dose for twice-daily products, and about 24 hours after the last dose for once-daily products such as Envarsus XR and Astagraf XL. Levels take several days to settle after a dose change, and FDA labeling calls for early, frequent trough checks after starting or stopping medicines that strongly change tacrolimus breakdown.

When to talk to a clinician

Contact your transplant team the same day if your level is above or below your target, or if you notice a new tremor, a bad headache, much less urine, swelling, a fever, or any sign of rejection your team has told you to watch for. Many hospitals ask the care team to call about levels above 20 ng/mL. Call 911 or your local emergency number for chest pain, seizure, severe trouble breathing, confusion or fainting.

Questions you could ask

  • What is my personal target range, and how long will it stay the same?
  • Should I always use the same lab and method for this test?
  • How often should this be checked?
  • Was my blood drawn at the right time relative to my dose?
  • Should we check my kidney function and potassium along with this level?
  • Could a new medicine, supplement or food be raising my level?

Questions people ask

What should my tacrolimus level be?

It depends on the organ you received, how long ago the transplant was, the other medicines you take and the tacrolimus product you use. For twice-daily Prograf, FDA labeling lists, for example, 7–20 ng/mL in months 1–3 and 5–15 ng/mL in months 4–12 for a kidney transplant with azathioprine, 5–20 ng/mL for a liver transplant, and 10–20 ng/mL then 5–15 ng/mL for a heart transplant. ARUP's published ranges for twice-daily tacrolimus span 5–20 ng/mL. Your team sets your personal target.

Why does my level change when I switch labs?

Labs measure tacrolimus with different methods. Immunoassays can also detect tacrolimus breakdown products, so they often read higher than LC/MS/MS, and the gap depends on the assay and the lab. For the clearest trend, have repeat levels done at the same lab, and ask your team before comparing numbers from different places.

Why is my blood drawn before my morning dose?

The trough, the lowest point before the next dose, is the number your team's target ranges are built around. A sample taken after a dose reads much higher and can wrongly look like a high level. Your team will tell you when to take the dose relative to your blood draw, so follow their instructions and tell the lab when you took your last dose.

Can foods or other medicines change my level?

Yes. Grapefruit and grapefruit juice can raise it, and many medicines either slow or speed up the way your body clears tacrolimus. FDA labeling calls for closer level checks when strong inhibitors or inducers are started or stopped. Tell your transplant team about every prescription, over-the-counter medicine and supplement you take.

How do I convert ng/mL to nmol/L?

Multiply ng/mL (the same as µg/L) by 1.243. So 10 ng/mL is about 12.4 nmol/L. To go the other way, multiply nmol/L by 0.804.

Show the science and sources

Units

  • 1 ng/mL = 1 ng/mL
  • 1 ng/mL = 1.244 nmol/L

Open the Tacrolimus unit converter

For clinicians and researchers

Tacrolimus is a macrolide calcineurin inhibitor (via FKBP12) and a CYP3A4/CYP3A5 and P-glycoprotein substrate. It is about 99% protein bound and strongly associated with erythrocytes; the whole blood to plasma ratio averaged 35 (range 12–67) in a US trial and depends on hematocrit, temperature, concentration and protein levels, so EDTA whole blood is the matrix of choice and heparin is not recommended. Half-life was about 32–34 hours in healthy volunteers and is longer in hepatic impairment (FDA labeling). Immunoassays cross-react with metabolites and can show a positive bias against LC/MS/MS that varies by assay and laboratory. FDA labeling trough ranges for twice-daily Prograf in adults: kidney with azathioprine 7–20 ng/mL in months 1–3 and 5–15 in months 4–12; kidney with MMF and an IL-2 receptor antagonist 4–11 ng/mL; liver 5–20 in months 1–12; heart 10–20 in months 1–3 and 5–15 from month 4; lung 10–15 in months 1–3 and 8–12 in months 4–12. ARUP's therapeutic ranges match: kidney 7.0–20.0 (0–3 months) and 5.0–15.0 (3 months and older); heart 10.0–20.0 and 5.0–15.0; liver 5–20 (1–12 months); toxic above 25 ng/mL. Once-daily products have separate targets, for example Envarsus XR in kidney transplant 6–11 ng/mL in month 1 and 4–11 ng/mL afterward, and a 7–16 then 5–15 ng/mL target in the Astagraf XL kidney trial. Trough concentrations from continuous IV infusion are not comparable with oral troughs. Hospital critical limits vary widely (median 20, range 14–60 ng/mL).

LOINC 11253-2 (primary), 77348-1, 74097-7, 74096-9, 76494-4. Specimen: whole-blood.

Sources

  1. Tacrolimus by Tandem Mass Spectrometry (test 0090612), ARUP Laboratories
  2. Prograf (tacrolimus) prescribing information, DailyMed, National Library of Medicine
  3. Envarsus XR (tacrolimus extended-release tablets) prescribing information, DailyMed, National Library of Medicine
  4. Astagraf XL (tacrolimus extended-release capsules) prescribing information, DailyMed, National Library of Medicine
  5. Drug Critical Limits for Urgent Physician Notification, Clinical Pharmacology & Therapeutics (Kuang, Ibrahim, Cheng, Kost) (2026)
  6. Tacrolimus (PubChem compound 445643), PubChem, National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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