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Test Code BLOD0645 Methotrexate

Important Note

Note: Specimens from patients who have received glucarpidase (Voraxaze, carboxypeptidase G2) as a high dose methotrexate rescue therapy should not be tested with this method. These patients have an increased level of metabolite that cross reacts with the methotrexate antibody. These metabolites stay in circulation for 5-7 days.


Enzyme Immunoassay


Following therapy, serum concentration of Methotrexate is used to judge whether the drug is being cleared appropriately and verify that a nontoxic concentration has been attained.  Methotrexate is used in the treatment of certain neoplastic diseases, severe psoriasis, and adult rheumatoid arthritis.

Performing Laboratory

Bozeman Health Laboratory Services

Specimen Requirements

Specimen Type: Plasma
Container/Tube: Light-green top (lithium heparin gel)
Specimen Volume: 2 mL
Specimen Minimum Volume: 1 mL

Collection Instructions: Spin down and separate cells within 2 hours of collection.  Ensure adequate centrifugation,  Fibrin, red blood cells and particulate matter may cause erroneous results.  Avoid repeated freeze/thaw cycles.

Specimen Rejection: Specimens from patients who have received glucarpidase (carboxypeptidase G2) as a high-dose methotrexate rescue therapy should not be tested with this immunoassay.

Specimen Transport Temperature


Specimen Stability


Specimen Type Temperature Time
Plasma Ambient 24 hours
  Refrigerated 14 days
  Frozen 1 month


Reference Values

Nontoxic drug concentration after 72 hours: ≤0.10 umol/L

Day(s) Test Set Up

Monday through Sunday, by appointment only.  Please call Bozeman Health Laboratory Services Chemistry Department at 414-5010 to schedule Methotrexate testing.

Test Classification and CPT Coding