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Methotrexate
Test CodeMTREX
Preferred Specimen
1 mL frozen serum collected in a red-top tube (no gel)
Patient Preparation
Collect 24, 48, or 72 hours after dose
Minimum Volume
0.2 mL
Other Acceptable Specimens
Plasma collected in: EDTA (lavender-top) tube, fluoride oxalate (gray-top) tube, sodium or lithium heparin (green-top) tube
Instructions
Protect from light. Record hours from last dose on specimen container and in the remark column on the test requisition.
Transport Container
Transport tube
Transport Temperature
Frozen
Specimen Stability
Room temperature: 24 hours
Refrigerated: Unacceptable
Frozen: 5 days
Refrigerated: Unacceptable
Frozen: 5 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Serum separator tube (SST) or any other tube with additives • Received thawed
Methodology
Immunoassay (IA)
Setup Schedule
a.m. Tues-Sun
Report Available
2-4 days
Reference Range
| <5.00 umol/L at 24 hours |
| <0.50 umol/L at 48 hours |
| <0.20 umol/L at 72 hours |
Clinical Significance
Methotrexate is an antimetabolite used in the treatment of certain neoplastic diseases, psoriasis and rheumatoid arthritis. In combination with other chemotherapeutic agents, high dose methotrexate doses followed by leucovorin rescue may be effective in prolonging relapse-free survival in patients with non-metastatic osteosarcoma. Methotrexate levels are monitored to assess toxicity.
