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Test Code LAB4143 METHOTREXATE LEVEL

Important Note

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

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.

Specimen Type

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

Test Limitations

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