Methotrexate Test: When and Why You Need It

Methotrexate is a powerful medication used to treat a range of health conditions, from autoimmune diseases like rheumatoid arthritis and psoriasis to certain types of cancers. While it can be highly effective, methotrexate can also lead to serious side effects if not monitored properly. That’s why regular methotrexate testing is essential for anyone undergoing treatment with this drug.

What Is Methotrexate?

Methotrexate is a disease-modifying antirheumatic drug (DMARD) that works by interfering with the growth of certain cells in the body, particularly those that reproduce quickly, such as cancer cells, bone marrow cells, and skin cells. It is commonly prescribed for:

Autoimmune diseases like rheumatoid arthritis, lupus, and psoriasis
Certain cancers, including leukemia, lymphoma, and breast cancer
Ectopic pregnancy, to terminate abnormal pregnancies

Despite its efficacy, methotrexate can be toxic at high levels, especially to the liver, kidneys, and bone marrow. That's where methotrexate level testing comes in—to ensure that the drug remains within a safe therapeutic range.

What Is a Methotrexate Test?

A methotrexate test measures the concentration of methotrexate in your blood. It is usually done after a high-dose methotrexate treatment, particularly in cancer therapy, to determine how quickly the drug is being eliminated from your body.

This test is crucial because high levels of methotrexate for prolonged periods can lead to severe toxicity, including:

Liver damage
Kidney dysfunction
Bone marrow suppression
Gastrointestinal toxicity
Skin and mucous membrane irritation

The methotrexate test is often accompanied by other blood tests to monitor liver function (LFT), kidney function (KFT), and blood cell counts (CBC).

When Is the Methotrexate Test Required?

1. High-Dose Methotrexate Therapy in Cancer Treatment

Patients receiving high doses (often intravenously) for cancer treatment must be monitored closely. Blood levels are usually measured at specific time intervals—such as 24, 48, and 72 hours post-dose—to determine how quickly the body is clearing the drug.

2. Signs of Toxicity or Overdose

If a patient shows signs of methotrexate toxicity—such as mouth sores, unusual bruising, bleeding, nausea, or fatigue—a methotrexate test can help assess if blood levels are dangerously high.

3. Monitoring Organ Function in Long-Term Use

For patients on low-dose oral methotrexate (such as in rheumatoid arthritis), the test may not be routine but is still crucial if:

There's any indication of liver or kidney impairment
The patient is taking interacting medications
The patient has missed doses or taken incorrect doses

Why Is the Methotrexate Test Important?

Prevents Toxicity – The primary purpose of methotrexate level testing is to prevent methotrexate toxicity, which can be life-threatening if not addressed early. By measuring blood levels at scheduled times, clinicians can take steps—such as administering leucovorin rescue therapy—to reduce harmful effects.
Guides Leucovorin Dosing – Leucovorin (folinic acid) is given to help protect healthy cells from methotrexate’s harmful effects. The dose and timing of leucovorin depend on methotrexate blood levels, so testing ensures accurate, personalized treatment.
Assesses Drug Elimination – Methotrexate is eliminated through the kidneys. In patients with reduced kidney function, the drug can accumulate to toxic levels. Monitoring helps assess whether elimination is delayed, and if additional hydration or medications are needed.
Helps Tailor Dosage – Methotrexate dosing isn’t one-size-fits-all. Regular testing helps doctors individualize the dosage for maximum benefit and minimum side effects.

How Is the Methotrexate Test Performed?

The test is a simple blood test. Here’s what you can expect:

A healthcare professional will draw blood from a vein, usually in your arm.
The blood sample is sent to a laboratory to measure methotrexate concentration.
Multiple samples may be taken over a few days after methotrexate administration (typically at 24, 48, and 72 hours).

No special preparation is needed, but it’s important to:

Inform your doctor of all medications and supplements you are taking.
Stay well-hydrated, as proper hydration helps eliminate methotrexate from the body.
Avoid alcohol and certain drugs that can affect liver and kidney function.

What Do the Test Results Mean?

Methotrexate levels are usually reported in micromoles per liter (μmol/L). Here’s a general guide (these numbers can vary based on institution protocols):

Time After Dose	Target Methotrexate Level
24 hours	< 10 μmol/L
48 hours	< 1 μmol/L
72 hours	< 0.1 μmol/L

If levels are higher than expected, your doctor may:

Extend leucovorin therapy
Increase fluid intake through IV hydration
Use medications like glucarpidase to rapidly lower methotrexate levels
Delay the next dose until levels return to safe range

Risks and Limitations of the Test

Timing is Crucial – The test must be performed at specific intervals. Delayed testing can give misleading results.
May Not Be Useful for Low-Dose Therapy – Routine methotrexate level testing is not usually required for patients on low-dose oral methotrexate unless there's suspicion of toxicity.
Other Monitoring Is Still Needed – This test doesn’t replace other vital tests like liver function tests (LFT), kidney function tests (KFT), and complete blood count (CBC), all of which should be monitored regularly.

Who Should Get a Methotrexate Test?

You may need a methotrexate test if you:

Are receiving high-dose methotrexate for cancer
Show signs of methotrexate toxicity
Have impaired kidney function
Are taking other medications that interact with methotrexate (like NSAIDs, penicillin, or sulfa drugs)
Have a history of delayed methotrexate clearance

How Often Is the Test Done?

In cancer patients, levels are checked every 24 hours after a high-dose infusion until levels are safe.
In autoimmune disease patients, the test is usually only done if symptoms suggest toxicity or in high-risk cases.
Routine tests like LFT, KFT, and CBC may be done every 1-3 months for long-term methotrexate users.

What Affects Methotrexate Levels?

Several factors can influence how quickly methotrexate leaves your system:

Kidney function
Age and body weight
Hydration status
Other medications
Genetic factors affecting metabolism

Your doctor will take all of these into account while planning your treatment and monitoring schedule.

Tips to Use Methotrexate Safely

Follow dosage instructions carefully—don’t skip or double doses.
Stay hydrated, especially after high-dose therapy.
Avoid alcohol and non-essential drugs that affect the liver.
Report any side effects, such as fatigue, ulcers, or unusual bleeding.
Go for regular monitoring, including methotrexate tests, CBC, liver and kidney panels.

Final Thoughts

Methotrexate is a valuable medication, but it requires careful monitoring to prevent complications. The methotrexate test is an essential tool that helps doctors ensure the drug is working effectively and safely, especially for patients receiving high-dose therapy or those at risk of delayed drug clearance.

If you're on methotrexate—or about to start—talk to your doctor about the importance of testing and regular follow-ups. Being proactive can make your treatment journey safer and more successful.