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Test Code MX Methotrexate

Important Note


***** Protect from light after collection. *****

Specimen and Container/Tube

Specimen Type: Serum

Preferred Specimen: Red Top (protected from light)

Specimen Stability

Storage Temperature

Stability

Room Temperature

24 hours

Refrigerated

14 days

Frozeb

 26 weeks

Note: Specimen must be protected from light.

Collection Instructions

Collect specimen per standard laboratory collection procedures. 

 

Specimen Handling and Transport Instructions

UCMC Onsite Instructions: 

Collect specimen per standard collection procedure and send to laboratory immediately. 

 

UCMC Offsite and UC MedLab Outreach Instructions: 

  • Samples should be centrifuged within 2 hours of collection.
  • Centrifuge specimens at >2500 x g for 10 minutes at room temperature.
  • Aliquot sample into a plastic transport tube protected from light containing a minimum of 0.2 mL of specimen.
  • Samples must be sent refrigerated at 2-8oC.

Rejection Criteria

  • Common specimen rejected situations include: incorrect specimen type, insufficient volume, missing or incomplete specimen identifiers, incorrect specimen transport, or specimens outside stability limits. 
  • Specimens that are clotted or grossly hemolyzed.
  • Specimens that were transported unspun/whole blood and draw time is greater than 6 hours.

Reference Values

The concentration of methotrexate in serum or plasma depends on the time of the last drug dose; mode of administration; concomitant drug therapy; sample condition; time of sample collection; and individual variations in absorption, distribution, biotransformation, and excretion.

 

Reference range subject to interpretation by ordering physician.

 

                  Potentially toxic serum concentrations:

 

                  >5 µmol/L (24 hours after high-dose methotrexate therapy).

                  >0.5 µmol/L (48 hours after high-dose methotrexate therapy).

                  >0.1 µmol/L (72 hours after high-dose methotrexate therapy).

 

Critical Values

Analyte

Unit

Low

High

Age

N/A

N/A

N/A

N/A

N/A

Turnaround Time

Turnaround times are relative to the time the specimen is received in the test laboratory. 

 

STAT Turnaround Time: 1 hour

Routine Turnaround Time: 4 hours

Testing Schedule: 24/7

Clinical Indications

Methotrexate is an antineoplastic agent that inhibits DNA synthesis. The medication exerts its effects through competitive inhibition of the enzyme dihydrofolate reductase thus decreasing the concentrations of tetrahydrofolate essential to the methylation of pyrimidine nucleotides and consequently the rate of pyrimidine nucleotide and ultimately DNA synthesis.

 

Methotrexate is used in the treatment of certain neoplastic diseases, severe psoriasis, and adult rheumatoid arthritis. Methotrexate is effective against malignancies characterized by rapid cell proliferation. Intermediate to high doses of methotrexate with leucovorin (citrovorum-factor or folinic acid) rescue to salvage nontumor cells have been used with favorable results in the treatment of osteogenic sarcoma, leukemia, non-Hodgkin lymphoma, lung, and breast cancer.

 

Methotrexate has the potential for serious toxicity. Patients undergoing methotrexate therapy are closely monitored so that toxic effects are detected promptly.

Test Components

Methotrexate
 

CPT Codes

80204

LOINC Codes

14836-1

Methodology

Syva Enzyme-Multiplied Immunoassay Technique (EMIT) (Siemens Healthcare Diagnostics)

Synonyms/Keyword Search

N/A

Additional Information

  • Important: Specimens from patients who have received glucarpidase (carboxypeptidase G2) as a high-dose methotrexate rescue therapy should not be tested with this immunoassay. Methotrexate concentrations should be performed using the liquid chromatography-tandem mass spectrometry method to avoid the reporting of falsely elevated methotrexate values due to an interference that could confuse the efforts of the glucarpidase therapy. After glucarpidase therapy, it can take at least 5 to 7 days before accurate measurements of serum methotrexate can be obtained using an immunoassay.

Last Review Date

6/4/25

Volume

Preferred Volume: 0.5 mL

Minimum Volume: 0.2 mL