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Test Code Lab481 Methotrexate, Plasma

Methodology

Enzyme Immunoassay 

Literature Reference:

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

Performing Laboratory

Barnes-Jewish Hospital Laboratory

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. 

 

Specimen Transport Temperature

Ambient

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.

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

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