At a Glance
Why Get Tested?
To detect and evaluate toxic concentrations of methotrexate
When to Get Tested?
At specific timed intervals after a high dose of methotrexate to monitor blood levels and guide treatment and whenever symptoms suggest methotrexate toxicity
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None, but timing of the sample for testing is important; when having your blood drawn, tell the laboratorian when you took your last dose of methotrexate.
The Test Sample
What is being tested?
This test measures the amount of methotrexate in the blood. Methotrexate is a drug that has been in use since the 1960s. It is primarily used to treat childhood acute lymphocytic leukemia, lymphoma, cancers of the lung, head, neck, and breast, and is also prescribed to treat rheumatoid arthritis (RA) and psoriasis. Methotrexate interferes with the vitamin folate, which slows the growth of cancer cells and decreases immune system activity. It acts as an anti-inflammatory and can help minimize the joint damage associated with RA.
Methotrexate must be carefully monitored. Even when used correctly, it can cause significant side effects. Increased concentrations can be toxic, potentially damaging the liver, kidneys, and lungs and suppressing cell production in the bone marrow.
The dose of methotrexate given depends upon the condition being treated. It is usually given once a week, with levels in the blood rising after a dose and then gradually falling. Methotrexate is eliminated from the body by the kidneys, so any condition that decreases kidney function or interferes with drug clearance has the potential to increase blood concentrations.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed, but timing of the sample for testing is important and the doctor may specify collection at a certain number of hours after a methotrexate dose.
Ask a Laboratory Scientist
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
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