Serum or Plasma Mass Concentration of Methotrexate

Why Is This Test Done?

Your doctor may order this test to check if your methotrexate dose is working properly, to detect low or high levels that could cause problems, or to ensure you’re not experiencing toxicity from the medication. It’s often done during chemotherapy, rheumatoid arthritis treatment, or other conditions where methotrexate is prescribed.

What Does This Test Involve?

A blood sample is taken from a vein in your arm. The sample is sent to a lab where it’s analyzed to measure methotrexate concentration. The test can be done on either serum (liquid part of blood after clotting) or plasma (liquid part after removing blood cells).

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for a few hours if your doctor specifies it. Wear comfortable clothing and plan to stay near the testing site for a short time after the draw.

What to Expect During the Test

You’ll lie down or sit comfortably while a healthcare provider inserts a small needle into your arm. A small amount of blood is collected into a tube. The process is quick and typically causes only minor discomfort.