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Test Code LAB481 Methotrexate

Notes:

Collection Time Guidelines
High Dose Collect 24, 48 and 72 hours after infusion
Low Dose Collect 30 minutes after IV dose. Collect 2 hours after PO dose.

Collection:

Specimen: Blood 

Preferred: Lt Green w/ Gel - Li Hep if analyzed within 4 hours of collection or Plain Red tube.

Acceptable: SST or Red Top if analyzed within 4 hours of collection or Plain Red tube.

Specimen Volume: 5 mL; Minimum 1 mL

 

Pediatric Collection:

Three Lt Green w/ Gel - Li Hep, Gold or Red microtainers filled to 600 uL.

Stability:

Once serum/plasma is separated from cells:

 

Ambient: 8 Hours

Refrigerated (preferred): 1 Week

Frozen: 2 Weeks

Turn Around Time (TAT):

STAT: 1 HOUR

Routine: 4 HOURS

Test Availability:

24 hours a day / 7 days a week

Performing Laboratory Section:

Chemistry / UMC MAIN LABORATORY

Reference Interval:

Interpretation by physician

Interpretive Data:

Physician must determine therapeutic range for each patient. IMPORTANT :  Specimens from patients who have received glucarpidase (carboxypeptidase G2) as a high dose methotrexate rescue therapy should not be tested with the ARK Methotrexate assay. These specimens have increased serum levels of 4-[[2,4-diamino-6-(pteridinyl)methyl]-methylamino]-benzoic acid (DAMPA) that result from metabolism of methotrexate by glucarpidase. DAMPA cross-reacts with the methotrexate antibody used in this assay, and may continue to circulate for at least five to seven days before accurate measurements of serum methotrexate may return. Oncologists on the clinical team should notify the laboratory when glucarpidase is administered to avoid the reporting of falsely elevated methotrexate concentrations.

 

Additional Test Codes

METHO