Mycophenolic Acid (MPA)
Measures the active form of mycophenolate (CellCept, Myfortic) in your blood. Transplant and autoimmune teams use it to see how much drug your body is getting.
AI-verified against cited sources. Awaiting expert reviewAlso called MPA, MMFLOINC 23905-3
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What it is
Mycophenolate mofetil (CellCept) and mycophenolate sodium (Myfortic) are medicines that quiet the immune system. They are used to help prevent organ rejection after a transplant and sometimes to treat conditions such as lupus nephritis. Your body turns them into mycophenolic acid (MPA), the active drug, and this test measures how much MPA is in your blood. The result depends a lot on how long after your last dose the blood was drawn.
Why it matters
People absorb and clear mycophenolate very differently, so the same dose can give very different blood levels. Most people take a fixed dose and don't need a blood level. Monitoring is used in selected situations, such as after a change in the medicine regimen, when interacting medicines are added, or when side effects or rejection are a concern. Some guidelines favor measuring total exposure over a dosing interval (AUC) rather than relying on a single trough level.
If it’s low
A low level means less mycophenolic acid is in your blood than is usual for your dose. A trough is the lowest point of the day, so a low number just before a dose is expected. A low trough doesn't always mean total exposure is low.
Common causes
- Blood drawn at the lowest point, just before the next dose
- Missed or late doses
- Taking cyclosporine, magnesium or aluminum antacids, proton pump inhibitors or some antibiotics that can lower mycophenolate exposure
- Taking the medicine with food, which lowers the peak
What can help
- Ask your team whether this result should change anything, since a single trough has limits
- Tell your team about antacids, acid reducers and antibiotics you take
If it’s high
A high level means more mycophenolic acid is in your blood than is usual for your dose. Research hasn't shown a clear link between a single high number and side effects, and one high number doesn't mean you will have problems. First check the timing, because a sample taken soon after a dose reads higher than a trough.
Common causes
- Blood drawn soon after a dose rather than just before the next one
- Taking tacrolimus, which tends to raise mycophenolate exposure
- A recent change in dose or formulation
- Day-to-day differences in absorption, which vary a lot between people
What can help
- Ask your transplant or lupus team how this result compares with the target they use
- Tell your team about every medicine and supplement you take
- Ask whether the sample was a trough or taken after a dose
What can affect your result
- Time since your last dose (peak vs trough)
- Formulation: mycophenolate mofetil or mycophenolate sodium
- Other medicines: tacrolimus tends to raise MPA exposure and cyclosporine tends to lower it; antacids, proton pump inhibitors and some antibiotics can lower it
- Food, which lowers the peak level
- Albumin level and kidney function, which change how much MPA is free (active)
- Timing of the draw: a sample taken soon after a dose reads much higher than a trough sample, and different formulations (mycophenolate mofetil vs mycophenolate sodium) are absorbed at different speeds.
- MPA is about 97% bound to albumin and the test usually reports total drug. A build-up of the MPAG metabolite (as in kidney impairment) or salicylate can raise the free fraction, so total MPA may understate free drug.
- Other medicines change exposure: magnesium or aluminum antacids, proton pump inhibitors (with mycophenolate mofetil) and drugs that interfere with enterohepatic recirculation can lower it, and tacrolimus and cyclosporine shift it in opposite directions.
- Food lowers the peak level (by about 40% in the FDA label's kidney transplant data).
Most often a trough, drawn just before the next dose. Some centers draw several timed samples over a dosing interval to estimate total exposure (AUC). A few days to settle after a dose change; the average half-life of MPA is about 18 hours after oral dosing.
When to talk to a clinician
Contact your transplant or care team promptly for fever, signs of infection, unusual bruising or bleeding, severe or lasting vomiting or diarrhea, or if you can't keep your medicine down. Talk with your team before changing or stopping mycophenolate because of a lab result. If you feel very unwell (for example, chest pain, trouble breathing, confusion or fainting), call 911 or your local emergency number.
Questions you could ask
- Why am I having this level checked?
- What level or exposure is my team aiming for?
- Was this sample a trough, or was it taken after my dose?
- Do you look at a single level or at my total exposure (AUC)?
- Could any of my other medicines or antacids be lowering my mycophenolate level?
- Should we recheck at the same time of day?
Questions people ask
What is a normal or target MPA level?
There is no single agreed target for one MPA number. Teams that monitor it usually look at total exposure over a dosing interval (AUC), often aiming for about 30 to 60 mg·h/L, which takes several timed samples. A single trough result is hard to interpret by itself, so ask your team what they use.
Is mg/L the same as mcg/mL?
Yes. 1 mg/L equals 1 mcg/mL. To get µmol/L, multiply by about 3.12, so 2.0 mcg/mL is about 6.2 µmol/L. To go the other way, multiply µmol/L by 0.3203.
Why does the time of the blood draw matter?
MPA rises after each dose and falls before the next one. A trough sample is the lowest point of the day, while a sample a couple of hours after a dose can read much higher. Your team will tell you when to have blood drawn.
Show the science and sources
Units
- 1 mcg/mL = 1 mcg/mL
- 1 mcg/mL = 1 mg/L
- 1 mcg/mL = 3.122 µmol/L
- 1 mcg/mL = 1000 ng/mL
For clinicians and researchers
MPA is the active metabolite of the prodrugs mycophenolate mofetil and mycophenolate sodium. It is about 97% bound to albumin and is mostly converted to the inactive phenolic glucuronide (MPAG), with enterohepatic recirculation. The mean apparent half-life is about 18 hours after oral dosing (FDA labeling). Total MPA is measured by immunoassay or LC-MS/MS, and free MPA is not routinely reported. Exposure is best described by the 12-hour AUC, and a target of about 30 to 60 mg·h/L is widely used in kidney transplantation. A 2026 Thai transplant guideline recommends against trough (C0) monitoring because C0 correlates poorly to fairly with AUC (r² 0.16 to 0.63), suggests AUC from limited sampling strategies when monitoring is justified, and notes that tacrolimus raises and cyclosporine lowers MPA AUC. In lupus nephritis, a 2024 meta-analysis found higher AUC and trough values in responders (AUC about 51 vs 30 mg·h/L; C0 about 2.5 vs 1.5 mg/L), but targets are not established, and AUC was not significantly related to adverse events. MPAG competes with MPA for albumin binding, and salicylate also raises the free fraction, so total MPA can understate free drug when albumin is low or MPAG is high. Molar conversion: 1 µmol/L is 0.3203 mg/L (molecular weight 320.3). MPAG is a separate marker.
LOINC 23905-3 (primary), 72667-9, 73680-1, 55806-4, 70211-8. Specimen: serum-or-plasma.
Sources
- CellCept (mycophenolate mofetil): prescribing information, U.S. Food and Drug Administration (DailyMed) (2026)
- Thai Transplant Care Practice Guideline on Immunosuppressive Therapy for Adult Kidney Transplantation, Nephrology (Carlton) (2026)
- Therapeutic drug monitoring of mycophenolic acid and clinical outcomes of lupus nephritis: a systematic review and meta-analysis, Lupus Science & Medicine (2024)
- Mycophenolic Acid (PubChem CID 446541), 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.