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Blood Test Tracker

Sirolimus

The amount of the immune-calming medicine sirolimus (rapamycin) in your blood, measured just before your next dose.

AI-verified against cited sources. Awaiting expert reviewAlso called SRLLOINC 29247-4

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What it is

Sirolimus, also called rapamycin, is a medicine that quiets the immune system. It is used to help prevent rejection after an organ transplant and to treat a rare lung condition called lymphangioleiomyomatosis (LAM). It is measured in whole blood, because most of the drug sits inside red blood cells. The sample is usually drawn right before your next dose, when the level is lowest (the trough).

Why it matters

Too little sirolimus may leave a transplanted organ with less protection against rejection. Too much is linked to more side effects, such as high cholesterol and triglycerides, low platelets and mouth sores. Each person clears the drug at a different speed, and many medicines and foods change the level, so teams use this test to fine-tune treatment. Sirolimus stays in the body for days, so a dose change takes a while to show up.

If it’s low

A level below your team's target means less sirolimus in your blood than planned. That can mean less protection against rejection, or less effect on the condition being treated. A missed dose or a draw taken long after the last dose is a common and harmless explanation, so teams often repeat the level first.

Common causes

  • Missed or late doses
  • Blood drawn long after the last dose
  • Medicines that speed up sirolimus breakdown, such as rifampin, carbamazepine, phenytoin or St. John's wort
  • A change from one form of sirolimus (tablet or liquid) to another
  • Lab method differences

What can help

  • Tell your care team about any missed doses and any new medicines or supplements
  • Ask whether the level should be repeated before anything changes
  • Talk with your care team before making any change to your medicine

If it’s high

A level above your team's target means more sirolimus in your blood than planned. This often has a simple cause, such as a blood draw taken too soon after a dose or a new medicine that slows the drug's breakdown, and it usually leads to a closer look rather than an emergency. Higher levels are linked to more side effects, so your team will look at the result along with your cholesterol, platelets and kidney tests.

Common causes

  • Blood drawn after the day's dose instead of before it
  • A recent dose increase
  • Medicines that slow sirolimus breakdown, such as some antifungal and macrolide antibiotic medicines
  • Grapefruit or grapefruit juice
  • Liver problems, which can slow clearance
  • Lab method differences (an immunoassay can read differently from 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 changing your level
  • Talk with your care 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: 3–18 ng/mL. Source: Quest Diagnostics, DailyMed, National Library of Medicine. Labs treat above 25 ng/mL as urgent.

What can affect your result

  • Time since your last dose: the sample should be drawn right before the next dose
  • Lab method: immunoassay and LC/MS/MS results are not interchangeable
  • Medicines, supplements and foods that change CYP3A4 activity, including grapefruit juice and St. John's wort
  • Liver function: labeling calls for dose changes and closer monitoring with liver impairment
  • Body weight: labeling calls for monitoring in people 13 or older who weigh under 40 kg
  • Taking sirolimus the same way each day, with or without food, because a high-fat meal changes how much is absorbed
  • Drawing the sample at the wrong time after a dose changes the result. Tell the lab when you took your last dose.
  • Immunoassays and chromatographic methods (LC/MS/MS) give different results, and FDA labeling says the two are not interchangeable.
  • Medicines and foods that change CYP3A4 activity, including grapefruit juice, change sirolimus levels in the body.
  • The usual sample is whole blood in an EDTA (lavender-top) tube.

Just before your next dose (about 24 hours after the last one), unless your care team says otherwise. Sirolimus has a long half-life (about 62 hours in kidney transplant patients), so FDA labeling advises staying on a new dose for 7 to 14 days before adjusting again based on a level.

When to talk to a clinician

Contact your transplant team the same day if you were told your level is above or below your target, or if you have a fever, a new cough or shortness of breath, mouth sores, swelling, or much less urine. Many hospitals ask the care team to call about levels above 25 ng/mL. Call 911 or your local emergency number for chest pain, severe trouble breathing, confusion or fainting.

Questions you could ask

  • What is my personal target range, and does it change over time?
  • 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 cholesterol, triglycerides, platelets and kidney tests along with this level?
  • Could a new medicine, supplement or food be raising my level?

Questions people ask

What is a good sirolimus level?

There is no single number. It depends on why you take sirolimus, what other medicines you take and which lab method was used. FDA labeling lists 5–15 ng/mL for lymphangioleiomyomatosis, and for kidney transplant after cyclosporine is stopped, 16–24 ng/mL in the first year and 12–20 ng/mL after that. Quest's general interval is 3.0–18.0 ng/mL. Your transplant team sets your personal target.

Why should I wait 1–2 weeks after a dose change before the next level?

Sirolimus leaves the body slowly, with a half-life of about 2.5 days in kidney transplant patients. FDA labeling advises staying on a new dose for at least 7 to 14 days before using a level to adjust it again, so the level reflects the new dose.

Do these targets apply if I take rapamycin for other reasons?

The ranges here come from transplant and LAM use. There is no established target level for other uses, and a lab's printed range is not a goal for them. Ask the clinician who prescribed it how to read your result.

Show the science and sources

Units

  • 1 ng/mL = 1 ng/mL
  • 1 ng/mL = 1.094 nmol/L

Open the Sirolimus unit converter

For clinicians and researchers

Sirolimus is a macrolide mTOR inhibitor (via FKBP12) and a CYP3A4 and P-glycoprotein substrate. It is extensively partitioned into red cells (mean blood-to-plasma ratio 36 ± 18) and about 92% protein bound, so whole blood is the matrix, collected in EDTA as a 24-hour trough. Terminal half-life is about 62 ± 16 hours in stable renal transplant patients, which is why FDA labeling advises waiting 7 to 14 days after a maintenance dose change before adjusting on a concentration. Labeling target ranges are chromatographic: 5–15 ng/mL in lymphangioleiomyomatosis, and after cyclosporine withdrawal in kidney transplant 16–24 ng/mL for the first year then 12–20 ng/mL; a trial with concurrent modified cyclosporine used 10–15 ng/mL, and a trial converting kidney transplant patients from calcineurin inhibitors used 8–20 ng/mL. Labeling states that concentrations depend on the assay and are not interchangeable between immunoassay and chromatography, so targets should be adjusted for the assay used, and that trough monitoring is recommended for everyone, particularly with altered metabolism, liver impairment, a change in dosage form or strong CYP3A4 inhibitors or inducers. Quest's LC/MS/MS interval is 3.0–18.0 ng/mL. Hospital critical limits vary widely (median 25, range 12–40 ng/mL).

LOINC 29247-4 (primary), 115766-8, 96462-7. Specimen: whole-blood.

Sources

  1. Sirolimus, LC/MS/MS (test code 36712), Quest Diagnostics
  2. Sirolimus prescribing information (FDA-approved labeling, generic of Rapamune), DailyMed, National Library of Medicine
  3. Drug Critical Limits for Urgent Physician Notification, Clinical Pharmacology & Therapeutics (Kuang, Ibrahim, Cheng, Kost) (2026)
  4. Sirolimus (PubChem compound 5284616), 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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