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Test Code MTREX Methotrexate

Important Note

Please call and verify with nurse: If patient is Post Glucarpidase, order code MTXSGM to Mayo.

Additional Codes

Hospital Ordering Code
LAB481  Methotrexate level

 

NOTE:

Specimens from patients who have received carboxypeptidase can contain a hydrolysis fragment of MTX (DAMPA) that cross-reacts with the methotrexate antibody used in this immunoassay.

Because enzyme immunoassay interference can result in overestimation of serum MTX concentrations immediately after administration of carboxypeptidase enzyme treatment (glucarpidase), it may be helpful to measure MTX after the glucarpidase dosing using a more specific assay (e.g. LC-MS/MS). The LC-MS/MS testing for MTX in these cases can be obtained by sendout to Mayo Medical Laboratories for "Methotrexate Post Glucarpidase, Serum." 

Specimen Requirements

Preferred Collection Container: 

Green NO Gel (Lithium Heparin)

 

Also Acceptable Collection Container: 

Red (No Additive)

 

Collection Information: 

Do not use gel separator tubes. Collect blood in a green no gel lithium heparin tube or serum red top tube.

 

Transport Information: 

Centrifuge and aliquot 0.6 plasma or serum into a transport tube.

 

Minimum Sample Volume: 

0.2 mL plasma or serum (approximately 0.4 mL of whole blood based upon a normal patient hematocrit)

Specimen Transport Temperature

Refrigerated Stability: 

3 days

 

Frozen Stability: 

6 months

 

Ambient Stability: 

12 hours

Performing Laboratory

Pathology Laboratory, UnityPoint Health, Des Moines

CPT

80204

Methodology

Immunoassay

Performance

Performed: 

Daily
24 hours a day

 

Analytical Time: 

2 hours