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Serum/plasma concentration of azathioprine (active metabolite, 6-mercaptopurine)

Published: August 9, 2026Updated: August 16, 2026

This test measures levels of azathioprine’s active breakdown product in your blood, which helps doctors monitor how your body processes this medication.

Quick summary

["This test helps ensure your medication dose is safe and effective for your treatment plan."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
73200-8
Short code
Pip+Tazo ind plt IgM SerPl Ql FC
Synonyms
Pip+Tazo ind plt IgM SerPl Ql FC
Category
hematology
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0.8
Ref high
1.2
Critical range
— – 5 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
flow-cytometry
CPT
85610
SNOMED
396252006
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Matters

Azathioprine is used to prevent organ rejection in transplant patients or to reduce inflammation in autoimmune conditions. Keeping levels in the right range helps prevent side effects like bone marrow suppression or excessive immune activity.

What to Expect Before the Test

No special preparation is needed, but you may need to fast for 8–12 hours if your test involves a blood draw for a specific time window (e.g., 24-hour collection). Always follow your healthcare provider’s instructions.

How the Test Works

A blood sample is taken from a vein in your arm. The lab then measures the concentration of azathioprine’s active metabolite using a sensitive immunoassay or similar method to detect very small amounts in your serum or plasma.

What the Results Mean

Results are compared to a target range set by your doctor based on your condition, medication dose, and other health factors. Too-high or too-low levels can affect how well your treatment works or increase risks.

Reference range

INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A

Specimen: serum

Inform your healthcare provider if you are taking blood thinners. No special preparation required.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Azathioprine Metabolite Level

Frequently asked questions

How often should I get this test?
Your doctor will determine the frequency based on your treatment plan. Typically, it’s checked monthly or as needed to adjust your dose if levels are outside the safe range.
What if my results are outside the target range?
If your levels are too high, your doctor may reduce your dose to lower the risk of side effects. If too low, they may increase it to improve treatment effectiveness. Always discuss changes with your provider.
Does diet or supplements affect this test?
Some foods or supplements (like garlic or high-purine foods) may interact with azathioprine, but they don’t directly affect this specific test. Stick to your prescribed medication schedule and avoid sudden changes without approval.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy