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Test Code LAB4143 METHOTREXATE LEVEL

Important Note

Specimens must be sent STAT to Sacred Heart Lab for testing immediately upon receipt.

Test Limitations

Specimens from patients who have received preparations of mouse monoclonal antibodies or carboxypeptidase G2 as a high dose methotrexate rescue therapy should not be tested by this method. 

Methotrexate results from this assay are not valid if the patient has received glucarpidase (carboxypeptidase G2) as a rescue therapy.

 

Specimen Type

Serum or plasma samples are acceptable specimens. For consistency, using the same matrix for individual patients is a good practice.

Preferred Specimen: Lithium Heparin Plasma (Mint Green Top, Dark Green Top)
Alternate Specimen: Serum (SST, Gold, Corvac, Tiger, Red Top Tube)  EDTA Plasma (Lavender Top)

Specimen Volume

1 mL

Minimum Volume

0.5 mL

Turnaround Time

STAT: 1 hour
Routine: 4 hours

Test Schedule

Daily on days and evenings

Sample Stability

Refrigerated: 14 days if removed from cells.

If testing will be delayed, specimens may be stored frozen proir to being tested. Care should be taken to limit the number of freeze-thaw cycles.

Method

Enzyme Immunoassay

Reference Ranges

 Methotrexate umol/L: Interpretation depends on dosing and draw times as well as target level for the disease being treated.

 

Reporting Limit

0.04 - 12,000 umol/L

Test Components

Methotrexate, umol/L

CPT Codes

80299