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Test Code Lab481 Methotrexate, Plasma

Performing Laboratory

Barnes-Jewish Hospital Laboratory

Methodology

Enzyme Immunoassay 

Literature Reference:

Package insert: ARK™ Methotrexate assay. ARK Diagnostics, Inc. 10/2011

Specimen Requirements

Specimen Type: Plasma

Container/Tube: Dark-green top (lithium heparin)

Specimen Volume: Full tube

Additional Information: Levels are generally drawn 24 hours after infusion and repeated at 24-hour intervals until level is <0.02 mcmol/L.  Specimens from patients who have received glucarpidase as a high dose methotrexate rescue therapy are unacceptable due to an interfering metabolite that causes invalid results. 

 

Day(s) Test Set Up

Monday through Sunday

Turnaround Time:
STAT: 1 hour after receipt in laboratory
Routine: 2-4 hours after receipt in laboratory

Test Classification and CPT Coding

80204

Reference Values

Conventional dose leukovorin rescue is used if the level is <5.0 mcmol/L at 24 hours after infusion.

High dose leukovorin rescue is used for higher values. Leukovorin rescue is continued until the level has fallen to <0.02 mcmol/L.

Critical result (automatic call-back): ≥5.0 mcmol/L

Literature Reference:

Waldman SA, Terzic A. Pharmacology and therapeutics, principles to practice. Saunders Elsevier, Philadelphia, PA: 2009.

Specimen Transport Temperature

Ambient

Additional Information

For BJH Laboratory Use Only
Alternate Tube:

1 red-top tube
1 mint green tube

1 dark green-top sodium heparin tube

1 lavender-top (EDTA) tube
Separator gel tube is acceptable


Analyte Stability:

  • Specimens must be processed within 8 hours.
  • Processed sample stability:
    • Ambient - 8 hours
    • Refrigerated (2 - 8°C) - 2 weeks
    • Frozen (≤ -20°C) - 6 months
  • See Analyte Stability Chart under General Information for a complete list.

 

Laboratory Processing Instructions:

Test performed in BJH Core Lab.  Processed by automated line for delivery to the Cobas 8000. Completed specimens are stored refrigerated for 5 days.

LOINC Code Information

Name LOINC Code
Methotrexate, Plasma 14836-1