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Test Code MTHX Methotrexate, Serum

Method Name

Enzyme-Immunoassay (EIA)

Specimen Type

Serum


Ordering Guidance


For patients that have received glucarpidase (carboxypeptidase G2) as a high-dose methotrexate rescue therapy, order MTXSG / Methotrexate Post Glucarpidase, Serum.



Shipping Instructions


Ship specimen in amber vial to protect from light.



Specimen Required


Supplies: Amber Frosted Tube, 5 mL (T915)

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Amber vial

Specimen Volume: 0.5 mL

Collection Instructions:

1. Methotrexate is sensitive to fluorescent light; avoid prolonged exposure of specimen to direct light.

2. Within 2 hours of collection, centrifuge the specimen.

3. For serum gel tubes, aliquot serum into a plastic vial within 2 hours of collection. Keep protected from light.

4. For red-top tubes, aliquot serum into a plastic vial immediately. Keep protected from light.


Specimen Minimum Volume

0.25 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 14 days LIGHT PROTECTED
  Frozen  28 days LIGHT PROTECTED
  Ambient  72 hours LIGHT PROTECTED

Reject Due To

Gross hemolysis Reject

Clinical Information

Methotrexate is an antineoplastic agent that inhibits DNA synthesis. The medication exerts its effects through competitive inhibition of the enzyme dihydrofolate reductase thus decreasing the concentrations of tetrahydrofolate essential to the methylation of pyrimidine nucleotides and consequently the rate of pyrimidine nucleotide and ultimately DNA synthesis.

 

Methotrexate is used in the treatment of certain neoplastic diseases, severe psoriasis, and adult rheumatoid arthritis. Methotrexate is effective against malignancies characterized by rapid cell proliferation. Intermediate to high doses of methotrexate with leucovorin (citrovorum-factor or folinic acid) rescue to salvage nontumor cells have been used with favorable results in the treatment of osteogenic sarcoma, leukemia, non-Hodgkin lymphoma, lung, and breast cancer.

 

Methotrexate has the potential for serious toxicity. Patients undergoing methotrexate therapy are closely monitored so that toxic effects are detected promptly.

Reference Values

Nontoxic drug concentration after 72 hours: <0.1 mcmol/L

Report Available

Same day/1 day

Performing Laboratory

Mayo Clinic Laboratories in Rochester

CPT Code Information

80204

Day(s) Performed

Monday through Sunday

Forms

If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.