Methotrexate, Serum
Use
Determining whether methotrexate is being cleared appropriately and verifying that a non-toxic concentration has been attained following therapy. Methotrexate is used in the treatment of certain neoplastic diseases, severe psoriasis, and adult rheumatoid arthritis. It is effective against malignancies characterized by rapid cell proliferation and involves monitoring of methotrexate to detect toxic effects promptly.
Special Instructions
For patients that have received glucarpidase (carboxypeptidase G2) as a high-dose methotrexate rescue therapy, order MTXSG / Methotrexate Post Glucarpidase, Serum. Ship specimen in amber vial to protect from light. Methotrexate is sensitive to fluorescent light; avoid prolonged exposure of specimen to direct light. Complete, print, and send a Therapeutics Test Request (T831) with the specimen if not ordering electronically.
Limitations
Specimens from patients who have received glucarpidase as a high-dose methotrexate rescue therapy should not be tested with this immunoassay. The results may be falsely elevated due to interference. It is advised to use liquid chromatography tandem mass spectrometry method to avoid reporting inaccuracies. After glucarpidase therapy, it can take 5 to 7 days before accurate measurements can be made using an immunoassay.
FDA ApprovedNew York Approved
Methodology
Immunoassay (EIA)
Biomarkers
LOINC Codes
- 14836-1
- 14836-1
Result Turnaround Time
1 day
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
0.5 mL
Minimum Volume
0.25 mL
Container
Amber vial
Collection Instructions
Within 2 hours of collection, centrifuge the specimen. For serum gel tubes, aliquot serum into a plastic vial within 2 hours of collection. Keep protected from light. For red-top tubes, aliquot serum into a plastic vial immediately. Keep protected from light.
Causes for Rejection
Gross hemolysis
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 72 hours |
| Refrigerated | 14 days |
| Frozen | 28 days |