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Methotrexate (MTX)

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EPIC Test Name

METHOTREXATE LEVEL

EPIC Code

LAB481

Specimen Requirements

plasma
Minimum Volume:0.5 mL
Collection:Collect using standard laboratory procedures
Transport:Room Temperature ASAP
Stability:Refrigerated: 1 week capped at 2-8 degrees C
Frozen: 1 year capped at -20 degrees C
Container:LIT-GRN
Rejection Causes:Insufficent Sample Volume

Methods

Competitive Homogeneous Immunoassay

Turnaround Time

SpecimenTurnaround TimeFrequency
plasmaStat: 90 minutes Routine: 4 hours24/7

Reference Ranges

Competitive Homogeneous Immunoassay
UnitTherapeutic Levels
umol/L<5.00 umol/L

Clinical Indications

• Methotrexate is used for treating several neoplastic and autoimmune diseases. As a chemotherapeutic drug, methotrexate is indicated in the treatment of gestational choriocarcinoma, chorioadenoma destruens, hydatidiform mole, acute lymphoblastic leukemia, non-Hodgkin's lymphomas, carcinomas of the breast and ovary, epidermal tumors of the head and neck, small-cell carcinoma of the lung, and non-metastatic osteosarcoma. As an immunosuppressant, it is used for psoriasis, rheumatoid arthritis, juvenile idiopathic arthritis, inflammatory bowel disease, systemic lupus erythematosus, vasculitis, and other connective tissue diseases.
• Methotrexate has distinct mechanisms of action when used in chemotherapy and immunosuppression. In cancer therapy, it acts as an antifolate antimetabolite through competitive inhibition of the enzyme dihydrofolate reductase, determining a reduction of DNA synthesis. In autoimmune diseases, different mechanisms are involved: increase of adenosine, which is an anti-inflammatory compound; modulation of the production of cytokine and adhesion molecules; induction of T cells apoptosis through the formation of reactive oxygen species.
• Since it is a nonspecific cytotoxin, prolongation of methotrexate blood concentrations may lead to severe, unwanted cytotoxic effects (myelosuppression, gastrointestinal mucositis, alopecia, cirrhosis, pulmonary fibrosis, acute kidney injury). To avoid these adverse events, methotrexate therapy is monitored following a methotrexate dose. Toxicity of methotrexate is reversed by leucovorin.
• Administration of high-dose methotrexate followed by Leucovorin rescue treatment showed effectiveness in treatment of carcinoma of the lung and osteogenic sarcoma.

Additional Information

• The methotrexate assay is a homogeneous immunoassay. Specimens from patients who have received glucarpidase should not be tested with this assay. These specimens have increased serum levels of 4-[[2,4-diamino-6(pteridinyl)methyl]-methylamino)-benzoic acid (DAMPA) resulting from the metabolism of methotrexate by glucarpidase. DAMPA cross-reacts with the methotrexate antibody and may continue to circulate for at least five to seven days, determining false positive results.
• Methotrexate (pKa 5.5) is mainly excreted via kidneys. Particular attention must be paid to maintaining output of a large volume of alkaline urine. Small reduced urine pH can cause significant reduction in its solubility. Keeping urinary pH alkaline can decrease the risks for intratubular precipitation of the drug and obstructive nephropathy during the treatment period.

Common Synonyms

ARK Methotrexate Assay SODIUM PARENTERAL

Performed

Lab
Chemistry - Downtown

Interpretative Information

Nontoxic methotrexate concentration after 72 hours is of <0.1 mcmol/L.

Methotrexate concentrations in serum/plasma are monitored during high-dose therapy (>50 mg/m2) in determining when Leucovorin rescue intervention should be initiated.
Threshold of potential toxicity following high-dose methotrexate:
• Methotrexate >10 µmol/L 24 hours after administration
• Methotrexate >1 µmol/L 48 hours after administration
• Methotrexate >0.1 µmol/L 72 hours after administration

CPT

80204

LOINC

14836-1

References

1. https://www.ark-tdm.com/products/cancer/methotrexate/pdfs/ARK_Methotrexate_Assay_Rev07_August_2017.pdf Accessed on 7/13/2021
2. Milone MC, Shaw LM. Therapeutic Drugs and Their Management – Methotrexate. In: Rifai N, Horvath AR, Wittwer C., eds. Tietz textbook of clinical chemistry and molecular diagnostic. 6th ed. St. Louis, Missouri: Elsevier, 2018. 821-822
3. Ferrari, V Sassoli, M Orlandi, et al.: Serum methotrexate (MTX) concentrations and prognosis in patients with osteosarcoma of the extremities treated with a multidrug neoadjuvant regimen. J Chemother. 5:135-141 1993 PMID 8515297
4. MV Relling, D Fairclough, D Ayers, et al.: Patient characteristics associated with high-risk methotrexate concentrations and toxicity. J Clin Oncol. 12:1667-1672 1994 PMID 8040679

Contact Information

Chemistry - Downtown: (315)464-4460
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