Sirolimus (Rapamycin), Whole Blood
Therapeutic drug monitoring for sirolimus/rapamycin — an mTOR inhibitor used clinically in transplant medicine, and increasingly discussed in longevity circles.
Included because rapamycin has become a prominent longevity topic. Level monitoring matters because the therapeutic window is narrow and side effects are dose-dependent — and because this is genuinely investigational territory for longevity use.
This is the most honest 'we don't know' on the site and it should stay that way. The trough ranges printed on a sirolimus report were derived to keep transplanted organs alive, which is a different risk-benefit calculation from anything a healthy person is doing. Intermittent weekly dosing — the pattern most longevity protocols use — does not produce a steady-state trough for those ranges to describe in the first place. Unproven is not the same as ineffective; it does mean nobody can tell you what number to aim for, and this page will not pretend otherwise.
Where did your sirolimus (rapamycin) level fall?
What to do next. There is no consumer target for this, and that is the honest answer. The intermittent low-dose protocols discussed in longevity circles are explicitly designed to avoid sustained immunosuppression, and they have no validated level. Grapefruit and any CYP3A4 inhibitor — including some supplements on this site, such as berberine and quercetin — raise sirolimus levels meaningfully. That interaction is real and not theoretical.
What Sirolimus (Rapamycin), Whole Blood actually measures — the analyte, and the assay
The specimen is whole blood, not serum, and that is not a technicality. Sirolimus partitions overwhelmingly into red cells, binding FK506-binding protein 12 inside them. A serum or plasma level would measure the small fraction left outside the cells and would vary with hematocrit, so every validated method lyses whole blood first Ivanova 2011.
Two method families are in use and they do not agree. Immunoassays — historically a microparticle enzyme immunoassay, now chemiluminescent and antibody-conjugated formats — use an antibody that also recognizes sirolimus metabolites. LC-MS/MS separates the parent drug from its metabolites and quantifies it against a stable-isotope internal standard Salm 2000 Ivanova 2011.
The immunoassay reads high, and the reason is metabolite cross-reactivity. Comparisons of chromatographic and immunoassay measurement of sirolimus in transplant recipients were performed precisely to quantify that positive bias Salm 2000 Zochowska 2006. A patient switched from one method to the other will see the number change with no change in dose.
Whole blood samples are also less stable than people assume. The stability of sirolimus and everolimus measured by immunoassay in whole blood from kidney transplant patients was studied for this reason Capone 2008 — storage time and temperature move the result, and hemolysis affects analytes measured on the same specimen Koseoglu 2011.
Sirolimus (Rapamycin), Whole Blood: what changes the blood, and what only changes the reading
What changes the sirolimus in you:
- The dose and the dosing interval. Sirolimus has a long terminal half-life — on the order of 60 hours in adults — so steady state takes roughly 5 to 7 days after any change, and weekly dosing regimens produce a concentration-time profile nothing like daily transplant dosing.
- CYP3A4 and P-glycoprotein. Sirolimus is a substrate for both. Grapefruit juice, ketoconazole, clarithromycin, diltiazem and ritonavir raise levels; rifampicin, carbamazepine and St John's wort lower them.
- Hematocrit. Because the drug lives in red cells, a change in hematocrit changes the whole-blood concentration for the same amount of drug in the body.
- Hepatic function, which governs clearance.
- Food. A high-fat meal changes absorption, which is why consistency with respect to food matters more than whether it is taken with food.
What changes only the reading:
- Immunoassay metabolite cross-reactivity, a positive bias that varies between patients because metabolite profiles vary Salm 2000 Zochowska 2006.
- A laboratory changing method mid-course, which shifts a series by more than most dose adjustments Lorde 2023.
- Drawing at the wrong point in the interval. The whole reference framework is a trough concentration; a peak read against a trough range is meaningless.
- Sample age and storage temperature Capone 2008.
- Incomplete red cell lysis, which under-recovers the drug.
- Hemolysis or an inadequately mixed EDTA tube Koseoglu 2011.
Reference interval or decision threshold — which kind of number Sirolimus (Rapamycin), Whole Blood is
This is a therapeutic drug monitoring target, derived in transplant recipients, for a purpose most readers of this page do not share. The published trough windows come from studies of graft rejection and drug toxicity in solid organ transplantation. They are outcome-derived, and the outcome is rejection.
The target is method-specific. Because immunoassay reads higher than chromatography, a trough range validated on one method is not the range for the other Salm 2000 Zochowska 2006.
There is no reference interval for a person not taking the drug, and no target concentration has been established for any non-transplant use. Nothing in the monitoring literature defines a concentration associated with a longevity outcome.
Trough concentration is a poor surrogate for exposure on intermittent regimens. The trough-to-area-under-the-curve relationship was established for continuous daily dosing; with weekly or less frequent dosing, a trough measured days after a dose is a point on a decay curve rather than a steady-state value Ivanova 2011.
How you would know your Sirolimus (Rapamycin), Whole Blood was wrong — and when to redraw
Seven days after a dose change, because five half-lives of a 60-hour drug is about 12 days and 5 to 7 days gets most of the way there. Measuring earlier reports a concentration that has not finished accumulating.
Always as a trough, immediately before the next dose, and with the time from the last dose recorded. On an intermittent regimen a level without that timestamp cannot be interpreted at all.
Conditions that must match: the same method — immunoassay and LC-MS/MS results are not interchangeable Salm 2000; the same laboratory; the same time from dose; the same concomitant drugs; and a sample analyzed within the laboratory's stability window Capone 2008.
What would have to change for the second number to mean something:
- Level higher than expected? Check the interacting drug list and the method before changing anything; an immunoassay result is expected to sit above a chromatographic one Zochowska 2006.
- Level changed after a laboratory switch? That is the method, not the patient Lorde 2023.
- Monitoring for adverse effects rather than efficacy? The numbers that move first are the lipid panel — sirolimus raises triglycerides and cholesterol characteristically — plus the CBC for cytopenias and urinalysis for proteinuria.
- Glucose or wound healing a concern? HbA1c and fasting glucose in the CMP belong on the same schedule, since mTOR inhibition impairs both insulin signaling and healing.
- Hematocrit changed substantially? The whole-blood concentration will move with it for the same body burden of drug; read the CBC beside the level.
What Sirolimus (Rapamycin), Whole Blood cannot tell you
It cannot tell you whether mTOR is inhibited in a tissue. A blood concentration is not a pharmacodynamic measurement, and the relationship between trough concentration and S6 kinase inhibition in any given tissue has not been established for non-transplant use.
It cannot be compared between methods, and the difference is systematic rather than random Salm 2000 Zochowska 2006.
It cannot be interpreted on an intermittent regimen using transplant reference windows, because those windows describe a different exposure profile Ivanova 2011.
It cannot predict the adverse effects, several of which — mouth ulcers, impaired wound healing, dyslipidemia — occur across the therapeutic range rather than above it.
The wrong inference readers actually draw is that a trough inside a published transplant range means a dose is right for them. Those windows were derived to prevent organ rejection on daily dosing measured by a specific assay, and none of the three assumptions holds for someone taking the drug weekly for something else Ivanova 2011 Salm 2000.
Sources read for these sections
- Zochowska D, et al. High-performance liquid chromatography versus immunoassay for the measurement of sirolimus: comparison of two methods. Transplantation Proceedings 2006 · PMID 16504669
- Capone D, et al. Stability of sirolimus and everolimus measured by immunoassay techniques in whole blood samples from kidney transplant patients. International Journal of Immunopathology and Pharmacology 2008 · PMID 18547473
- Salm P, et al. The quantification of sirolimus by high-performance liquid chromatography-tandem mass spectrometry and microparticle enzyme immunoassay in renal transplant recipients. Clinical Therapeutics 2000 · PMID 10823375
- Ivanova M, et al. High-throughput LC-MS/MS method for monitoring sirolimus and everolimus in the routine clinical laboratory. Clinical Chemistry and Laboratory Medicine 2011 · PMID 21574883
- Lorde N, et al. Impact of Variation between Assays and Reference Intervals in the Diagnosis of Endocrine Disorders. Diagnostics (Basel) 2023 · PMID 37998589
- Koseoglu M, et al. Effects of hemolysis interferences on routine biochemistry parameters. Biochemia Medica 2011 · PMID 22141211
Where to start with Sirolimus (Rapamycin), Whole Blood
In this order. Start at the supplement and you learn nothing, because you never established the number was real.
You have the range, where it came from and the first two moves. Inside is the rest of the five-pathway protocol — supplements, hormones, peptides — the order to run them in, and what to change when the number will not move.
Get the full protocol — $10/mo →📚 Transplant therapeutic drug monitoring guidance. Mannick JB et al., Sci Transl Med 2014 — mTOR inhibition and immune function in older adults.
🩸 Test your Sirolimus (Rapamycin), Whole Blood
Order directly through Marek Diagnostics — no doctor's visit needed, drawn at any Quest location in the US. Code CAMERON applies 10% off automatically.
Order this test — 10% off → Browse all 103 markers →What Sirolimus (Rapamycin), Whole Blood is usually tested alongside
One marker is a data point. These panels add the markers that make Sirolimus (Rapamycin), Whole Blood interpretable, name why each is on the list, and load the set into your cart at 10% off.
includes this + 8 more markers — Taking rapamycin off-label on a weekly or intermittent longevity protocol. This panel exists because the compound is being used outside the setting its evidence comes from, and almost everything that matters about it is measurable.
What people use Sirolimus (Rapamycin), Whole Blood to decide
Nobody orders a test for its own sake. Sirolimus (Rapamycin), Whole Blood is on the test list for these pathways — each one links to what the pathway claims, and what its test list is read for before you spend anything on it.
Fasting insulin and IGF-1 are the two readable outputs of the nutrient-sensing system this whole pathway targets. They also tell you whether an intervention is doing anything, which nothing else here does.
What moves your Sirolimus (Rapamycin), Whole Blood
1 compound in the Vault have a documented effect on this marker, or are a reason to have measured it first:
Browse all 278 compounds & 371 supplements →
Why your Sirolimus (Rapamycin), Whole Blood might be wrong
Most abnormal results are interference, not disease. Check these before you change anything. Each says whether the number is wrong (repeat it), badly timed (redraw it), or real with a cause.
Reported against a trough range. Timing relative to the dose is the single largest determinant of the number.
Draw immediately before the next dose.
Grapefruit, clarithromycin, azole antifungals and many others raise levels substantially; rifampicin and St John's Wort lower them.
This is a narrow-window drug — any new medication or supplement needs prescriber review.
What Sirolimus (Rapamycin), Whole Blood means in combination
One marker tells you a little; combinations tell you the story. These are the named patterns this one takes part in.
Both are narrow-therapeutic-window drugs reported against a trough range, and timing relative to the dose is the single largest determinant of the number. A lithium drawn four hours after the dose is far higher than the same person's true trough.
Lithium: exactly 12 hours after the evening dose. Sirolimus: immediately before the next dose. New medications matter enormously — NSAIDs and diuretics raise lithium, CYP3A4 inhibitors raise sirolimus. Tremor, vomiting or confusion on lithium is toxicity and an emergency.
What to test next
These put Sirolimus (Rapamycin), Whole Blood in context — each with its own full breakdown.
Frequently asked questions
Transplant therapeutic ranges 4–20 ng/mL depending on protocol; longevity protocols use intermittent, much lower exposure. Ranges vary by laboratory and assay — always compare to the range printed on your own report.
There is no established 'optimal' level for longevity use — that's an honest limitation. Clinical ranges apply to transplant indications. Interpretation belongs to the prescriber; see the result-category block on this page.
Immunosuppression, mouth ulcers, impaired wound healing, dyslipidemia, and glucose intolerance.
Sub-therapeutic for clinical indications.
You can order Sirolimus (Rapamycin), Whole Blood directly through Marek Diagnostics without a doctor's visit — drawn at any Quest Diagnostics location in the US. Code CAMERON applies 10% off automatically.
Where this goes next
The pages here are the frameworks. The protocols — the dosing, the order to correct things in, the week-by-week schedule and what to retest — are inside Skool.