Sign in →

Test Code MTXX or LAB481 Methotrexate Level, Serum 

Important Note

From the point of collection, methotrexate specimens must be protected from light.

 THIS IS NOT A SEND OUT TEST - BRING SERUM DIRECTLY TO CHEMISTRY DEPARTMENT

NOTE:Specimens from patients who received glucarpidase as a high dose methotrexate rescue therapy should not be tested with the Roche MTX assay. These samples contain significant concentrations of DAMPA, a cleavage product that is generated from MTX by glucarpidase. DAMPA cross-reacts significantly with immunoassay methods and methotrexate results would be falsely elevated. Oncologists on the clinical team should notify the laboratory when glucarpidase is administered.   In these cases the Mayo Clinic Laboratory test MTXSG (Methotrexate Post Glucarpidase) which uses Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS), should be performed.

 

Specimen Requirements

Container Type:

Optimal: Red

Acceptable: Gold, 

 

Note: While heparinized plasma is an accpetable sample for this test, it is not acceptable for the potential Mayo sendout test which may be needed. See notice above for details.
Optimal Collection Volume: 

4.5mL; full tube
Minimum Volume:
  • Adults: 1 mL whole blood
  • Neonates: 1 microtainer (400-600 uL)
Collection Instructions:

1. Protect the specimen from light by wrapping it in foil.

2. Gently invert the sample 5-6 times after collection.
Specimen Transport:

Refrigerate
Processing Instructions: 

1. If serum, allow the specimen to clot for 30 minutes.

2. Centrifuge specimen within 2 hours of collection.

3. After centrifugation, transfer the serum or plasma into an amber vial, which protects the sample from light.

        

4. Cover the entire sample with foil if no amber vials are available.

5. Keep the serum or plasma refrigerated until testing can be performed.

Specimen Stability

Specimen Type Temperature Time
Serum or Plasma Refrigerated 7 days
Room Temperature 72 hours
Frozen 28 days

Specimen Rejection Criteria

Hemolysis

Mild OK; Moderate OK; Gross Reject

Lipemia

Mild OK; Moderate OK; Gross Reject

Icterus

Mild OK; Moderate OK; Gross Reject

Other

Quantity not sufficient

Specimen not protected from light

Useful For

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.

Methodology

Roche cobas - homogeneous immunoassay

Reference Ranges

Methotrexate proposed therapeutic ranges

Post-Dose Time Therapeutic Range and Reporting Units
24 hours < 5.00 umol/L
48 hours < 0.50 umol/L
72 hours < 0.05 umol/L

 

Interpretive

No precise relationship between methotrexate serum levels and anti-neoplastic efficacy has been established, although levels <0.02 mmol/L were seen as necessary for the resumption of DNA
synthesis.

Day(s) Performed

24/7

Expected TAT

Same day

Performing Laboratory

Bronson Laboratory, Chemistry - Kalamazoo

Sample Retention Time

7 days

CPT Code

80299

LOINC Code

14836-1