Methotrexate

Test Code

METHX

CPT Codes
80299

Preferred Specimen

SST; Red

Minimum Volume

0.5 mL

Other Acceptable Specimens

Lithium Heparin Plasma (green top) tube

Instructions

Protect specimen from light using a brown paper sack, aluminum foil, or a dark-colored specimen tube.

Transport Container

Serum (gold top) tube or Lithium Heparin Plasma (green top) tube

Transport Temperature

Room Temperature or Refrigeration

Specimen Stability

Room Temperature - 4 hours; Refrigerated - 24 hours

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

Quantity Not Sufficient, IV contamination

Methodology
Turbidimetric

Setup Schedule

Daily upon receipt

Report Available

Upon completion of analysis

Limitations

Aminopterin, an antineoplastic agent not usually administered concurrently with methotrexate, and 4-amino-4-deoxy-N10-methylpteroic acid (APA), a minor metabolite of methotrexate, cross-react significantly with this assay.

Reference Range

A serum methotrexate concentration above 5 umol/L (5 x 10-6 mol/L) at 24 hours after high-dose therapy generally indicates a risk of toxicity. This maximum level is provided only as a guide; individual patient results should be interpreted in light of all clinical signs and symptoms.

Clinical Significance

Methotrexate is an antineoplastic agent that inhibits the enzyme dihydrofolate reductase. Such inhibition causes a stoppage of synthesis of tetrahydrofolate that, in turn, results in an inhibition of nucleotide and ultimately of DNA synthesis.

Methotrexate is effective against malignancies with rapid cell proliferation such as acute lymphoblastic leukemia, choriocarcinoma, trophoblastic tumors in women, and carcinomas of the breast, tongue, pharynx, and testis. It can also be used in the treatment of rheumatoid arthritis.

When used as an antineoplastic agent against these tumors, methotrexate is administered at high dose (2.5 mg/kg or 3.3 mg/kg), and usually is followed by leucovorin (folinic acid) rescue to salvage nontumor cells.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.