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Test Code LAB481 Methotrexate Level, Blood

Performing Laboratory

St. Louis Children's Hospital Laboratory - Chemistry

Specimen Requirements

Patient Preparation: None

Collection Container/Tube:

Preferred: Mint green-top lithium heparin (MNTGRN LiHep) tube

Acceptable: Plain red-top tube or Gold SST gel tube

Submission Container/Tube: If specimen is coming from outside facility and collected in a plain red-top tube aliquot processed sample into a plastic vial for transport (labeling specimen type on aliquot).

Specimen Collection Volume: 1.0 mL (minimum 0.6 mL)

Special Instructions: None

 

Sample Rejection

Specimens that are grossly hemolyzed

Mislabled or unlabeled specimens

Logistics

Test Availability: Monday-Sunday

Cut-off time: None, performed as received

Turnaround Time: Same Day; 2 hours from receipt in performing lab

Reference Values

Reference Interval: 

No reference intervals established 

results are reported as micromoles per liter (micromol/L)

NOTE: Therapeutic methotrexate levels are unique to individual patients and the time a sample is collected. Therefore, a set therapeutic range does not apply

Critical Value: None established

 

Methodology

Enzyme Immunoassay

Limitations

  • Specimens from patients who have received preparations of mouse monoclonal antibodies for diagnosis or therapy may contain human anti-mouse antibodies (HAMA). HAMA present in serum may interfere in immunoassays.

Additional Information

FOR SLCH CORE LABORATORY USE ONLY

Lab Processing Instructions: Centrifuge to separate. If specimen is collected in plain red-top tube aliquot sample into a Roche false-bottom tube for testing (labeling aliquot with specimen type).

Processed Volume: 0.3 mL plasma/serum

Analyte Stability:

Specimen Type Temperature Time
Whole Blood (unprocessed)  Ambient NA
Plasma/Serum (processed) Refrigerated (preferred)   2 weeks
  Ambient  24 hours
  Frozen  16 weeks   

Test Classification and CPT Code

14836-1

LOINC

80204

Last Reviewed

06/2025