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Test Code LAB481 Methotrexate Level, Blood

Important Note

PROTECT FROM UV LIGHT.

 

If patient has received glucarpidase (carboxypeptidase G2), refer to Note section at the bottom of this page.

Clinical System Name

Methotrexate Level Bld

Synonyms

MTX

Sample Requirements

Specimen: Whole blood

Container(s): Lt. Green/Mint Top Lithium Heparin, Lt. Green/Lithium Heparin Microtainer, Gold SST, Gold Microtainer, Dark Green/Sodium Heparin, Red

Preferred Vol: 1.0 mL

Minimum Vol: 0.5 mL

 

Note:   Protect sample from light. In-patients: wrap paper towel around tube and seal with one piece of tape. Off-site:  wrap tube in foil.  Specimen stable under fluorescent lighting for up to 4 hours.  

 

Note time and date of drug administration, and blood collection.  Draw times are determined by the treatment protocol; call Core Chemistry (206) 987-2578 for assistance in determining draw times.        

          

Processing Instructions

Reject due to: prolonged light/UV exposure, age of specimen

Spin: Y

Aliquot: Y

Storage location:  Core 5 Chemistry Refrigerator  

 

Off-site collection: Specimen should be centrifuged within 2 hours of collection. Spin blood and transfer serum or plasma to plastic tube and protect from light by wrapping tube in foil. Refrigerate or freeze. Note time of collection. 

Stability

Specimen Type Temperature Time

Serum or Plasma

 RT

≤ 4 h

Serum or Plasma

2-8 C

≤ 2 w

Serum or Plasma

-20 C or -70 C

≤ 1 y

Availability

STAT Performed TAT
Y 24/7 1 h

Performing Laboratory

Seattle Children's Laboratory    

Department

Department: Core Chemistry

Phone Number: 206-987-2102

CPT Codes

80204

Methodology

Method: Enzyme immunoassay by Vitros 4600

Analytical Volume:  0.150 mL

Reference Range

Contact Core Chemistry (206) 987-2578 for expected levels.

Note

Administration of glucarpidase (carboxypeptidase G2) to prevent toxicity in a patient with renal dysfunction will cause build up of the inactive metabolite DAMPA. DAMPA cross reacts with MTX in the immunoassay method. Patients who have received glucarpidase must have MTX measured by LC-MS/MS (at UW) after glucarpidase administration. Samples must be received by UW Lab by 9:00am for same day results.