Methotrexate (MTX), Serum or Plasma

CPT: 80299 80375
Updated on 2/6/2019
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Test Details

Synonyms

  • Rheumatrex®
  • Trexall™

Use

Methotrexate, either alone or in combination regimens depending on the patient's risk factors, have been very effective in women with choriocarcinoma and related trophoblastic tumors. Cures have been reported in most individuals treated with low doses of methotrexate plus leucovorin.

Although methotrexate induces complete remissions in acute lymphocytic leukemia of childhood, it is of more value for maintenance therapy and is an agent of choice in combination with mercaptopurine. Furthermore, intrathecal methotrexate and cranial irradiation are administered routinely to patients with acute lymphocytic leukemia to prevent meningeal metastases.

Methotrexate is a component of combination regimens used to treat non-Hodgkin and Burkitt lymphomas and breast, lung, bladder, cervical, gastric, and ovarian carcinomas. High-dose methotrexate plus leucovorin rescue (with or without other drugs) is used to treat osteogenic sarcoma, some non-Hodgkin lymphomas, and (by some physicians) head and neck tumors.

Methotrexate is a primary agent in the treatment of cutaneous T-cell lymphomas and medulloblastoma. It has shown activity as a single agent against testicular cancer; bladder, lung, colorectal, esophageal, hepatocellular, and cervical carcinomas; soft tissue sarcomas; and embryonal rhabdomyosarcoma. For some of these neoplasms (testicular, colorectal, and hepatocellular cancers; soft tissue sarcomas and rhabdomyosarcoma) more effective regimens are available and are used much more frequently than methotrexate.

Limitations

This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.

This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.

Methodology

Liquid chromatography/tandem mass spectrometry (LC/MS-MS)

Reference Interval

Therapeutic: 0.02−5.00 μmol/L

Critical Value

Potentially toxic: after 24 hours: >5.00 μmol/L, after 48 hours: >0.50 μmol/L, after 72 hours: >0.05 μmol/L

Additional Information

Methotrexate is an antimetabolite that combines with dihydrofolate reductase and therefore interferes with the synthesis of tetrahydrofolic acid necessary for DNA synthesis. From 40% to 50% of a small dose and up to 90% of a larger dose is excreted unchanged in the urine in 48 hours, a major portion of it during the first eight hours. Toxicity consists of bone marrow depression with megaloblastosis. Concomitant salicylate administration increases incidence of toxicity, due to diminished renal tubular excretion. The effect of methotrexate on normal cells may be reversed by administration of 5-formyltetrahydrofolate, also called citrovorum factor or leucovorin. This “rescue” makes possible administration of much higher doses of methotrexate than the body would otherwise survive. The initial half-life is two to four hours but the total body clearance (terminal) half-life is 8 to 15 hours.

Specimen Requirements

Specimen

Serum or plasma

Volume

1 mL

Minimum Volume

0.3 mL

Container

Red-top tube, lavender-top (EDTA) tube, or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.

Collection

Transfer separated serum or plasma to a plastic transport tube. Collection is determined by dosing protocol.

Storage Instructions

Room temperature

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Gel-barrier tube

Clinical Information

References

American Medical Association, Division of Drugs and Toxicology. Drug Evaluations Subscription. Chicago, Ill: AMA, Spring, 1993.

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
007658 Methotrexate (MTX), Serum 14836-1 007658 Methotrexate (MTX), Serum umol/L 14836-1

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