Cyclosporine (Trough)
Measures how much cyclosporine, an anti-rejection and immune-calming medicine, is in your blood just before your next dose.
AI-verified against cited sources. Awaiting expert reviewAlso called CsA, CYALOINC 3520-4
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What it is
Cyclosporine (brands include Neoral, Sandimmune and Gengraf) calms the immune system. It is used to help prevent rejection after organ transplants, and some forms are used for autoimmune conditions such as severe rheumatoid arthritis and psoriasis. The trough level, also called C0, is drawn right before your next dose, when the level is lowest. It is measured in whole blood, not serum.
Why it matters
Too little cyclosporine can leave a transplanted organ less protected from rejection. Too much can strain the kidneys and raise blood pressure, among other effects. How much drug your body absorbs differs a lot from person to person, so doctors use the trough level to fine-tune treatment. Your target is set by your care team and depends on the organ, the time since transplant, your other medicines and the lab method.
If it’s low
A level below your team's target can mean less protection against rejection or flare-ups of the condition being treated. It can also be expected at some stages of treatment. A low level alone does not mean rejection is happening.
Common causes
- Missed or late doses
- Medicines that speed up breakdown, such as carbamazepine, phenytoin, phenobarbital, rifampin and St. John's wort
- Poor absorption, for example from diarrhea or some stomach and bowel problems
- A change in brand or product that delivers less of the drug
What can help
- Tell your team about missed doses, vomiting or diarrhea soon after a dose
- Use reminders or a pill organizer
- Ask your team before any brand or generic switch
If it’s high
A level above your team's target means more cyclosporine exposure than planned. That raises the chance of side effects such as kidney strain, high blood pressure, tremor, high potassium and low magnesium. A high number does not always mean you feel unwell, and your team will weigh it with your symptoms and kidney tests.
Common causes
- A sample drawn after the morning dose instead of before it
- Medicines or foods that slow cyclosporine breakdown, such as diltiazem, verapamil, clarithromycin, erythromycin, some antifungals and grapefruit juice
- Switching between cyclosporine brands or generics, since Neoral-type and Sandimmune-type products are not interchangeable
- Reduced liver function, which can slow clearance
- Extra doses taken by mistake
What can help
- Tell your transplant team before starting or stopping any medicine, supplement or grapefruit juice
- Ask your team about a daily routine that keeps dose timing and meals consistent, and use reminders
- Bring a high result to your team promptly instead of changing the dose yourself
What can affect your result
- Timing of the draw: it must be a true trough before the next dose
- The assay method: immunoassay and LC-MS/MS differ, and results from different labs are not interchangeable
- The organ transplanted, the time since transplant and the other immunosuppressants used
- The product: Neoral-type (modified) and Sandimmune-type capsules are not bioequivalent
- Drug and food interactions, including grapefruit juice
- Liver function, diarrhea and consistency of dose timing around meals
- A sample drawn after the morning dose is not a trough and will read falsely high.
- It must be measured in whole blood (EDTA). Plasma or serum values are much lower and not comparable (plasma may be one-half to one-fifth of whole blood, per the FDA label).
- Older nonspecific assays also detected metabolites and read roughly twice as high as methods that measure only the parent drug. Immunoassay and LC-MS/MS results are not interchangeable, so compare results only from the same lab and method.
Just before the next dose (the trough, or C0). For twice-daily dosing this is usually about 12 hours after the last dose. The terminal half-life is about 19 hours (range 10 to 27), so levels take a few days to settle after a dose change or a new interacting medicine.
When to talk to a clinician
Contact your transplant team the same day if you miss doses, vomit soon after a dose, or notice much less urine, new swelling, a sudden rise in blood pressure, severe headache, confusion, seizures or fever. A result outside your target should be reviewed by your team promptly. Call 911 or your local emergency number for chest pain, trouble breathing or a seizure.
Questions you could ask
- What is my personal target range, and does it change over time?
- Which medicines, supplements or foods should I check with you before using?
- Was my blood drawn before my dose?
- Should my kidney function, potassium or blood pressure be checked more often?
- Could a missed dose or another medicine explain this result?
- Should we recheck the level soon?
Questions people ask
What is my target level?
There is no single number. Your team chooses a target based on your transplant or condition, how long you have been on treatment, your other medicines and the lab method. The FDA label says no fixed relationship between levels and outcomes has been established, so use the range your team gives you.
Why must blood be drawn before my morning dose?
The trough is the lowest level in the dosing cycle and is the value most teams track. If you take your dose first, the result reads falsely high and can lead to unneeded dose changes.
Can I compare results from different labs?
Not safely. Methods differ, and the FDA label says assay results are not interchangeable. Try to use the same lab and method for trends.
Show the science and sources
Units
- 1 ng/mL = 1 ng/mL
- 1 ng/mL = 0.8315 nmol/L
Open the Cyclosporine unit converter
For clinicians and researchers
Cyclosporine is a cyclic undecapeptide calcineurin inhibitor metabolized mainly by CYP3A4 and a P-glycoprotein substrate, with a terminal half-life of about 19 hours (range 10 to 27) and mostly biliary elimination. It distributes into red cells in a temperature-dependent way, so whole-blood EDTA samples are required. The FDA label notes that plasma concentrations may be one-half to one-fifth of whole-blood values, that older nonspecific assays read roughly twice as high as parent-drug-specific assays, and that assay results are not interchangeable. The Sandimmune label states that no fixed relationship between levels and outcomes has been established and that the type of assay matters. The modified-capsule label adds that the transplanted organ and other immunosuppressants matter and that most clinicians base monitoring on trough concentrations. As an example, one series of 375 renal transplant recipients was managed to 24-hour whole-blood troughs of 100 to 200 ng/mL by HPLC, which is not a general target. A table in the modified-capsule label for kidney transplants lists a trough above 200 ng/mL among features favoring cyclosporine nephrotoxicity and below 150 ng/mL among features favoring rejection (the table says serum trough, from older practice; current testing uses whole blood). One reference laboratory (ARUP, LC-MS/MS) prints a general therapeutic range of 100 to 400 ng/mL and separate ranges by organ and time since transplant, and states that the best range for a person can differ. For a given trough, exposure is higher with Neoral-type modified formulations than with Sandimmune. The 2-hour post-dose (C2) level is a different test with different values and must not be plotted with C0. Conversion: 1 ng/mL = 0.832 nmol/L (MW 1202.6).
LOINC 3520-4 (primary), 53828-0, 55805-6, 14978-1, 108279-1. Specimen: whole-blood.
Sources
- Sandimmune (cyclosporine) prescribing information (Dosage and Administration: Blood Cyclosporine Concentration Monitoring; Clinical Pharmacology), U.S. FDA label via NLM DailyMed (Novartis) (2026)
- Cyclosporine capsules USP (modified) prescribing information (Blood Concentration Monitoring in Transplant Patients; Warnings), U.S. FDA label via NLM DailyMed (Teva Pharmaceuticals) (2024)
- Cyclosporine (PubChem CID 5284373), 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.