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Test Code MTX Methotrexate Level

Patient Preparation

No special patient preparation required

Special Collection Instructions

Customarily, draw at 24 hour intervals after start of infusion; although earlier and more frequent monitoring may be indicated.

Collection Method

Venous collection

Minimum Volume

1 mL

Container

Lt Green / Plasma Separator / Lithium Heparin

Preferred Specimen

Light Green Top (lithium heparin) plasma

Acceptable Specimens

Serum:

  • Gold Top SST
  •  
  • Red Top


Plasma:

 

  • Light Geen Top (lithium heparin)
  • Purple or Pink Top(K2/K3 EDTA)
  • Dark Green Top (sodium heparin)

 

Reference or Target Ranges

<0.04 umol/L

Reportable Units

umol/L

Critical Value

>5 umol/L &commat; 48 hours

Reasons for Rejection

 


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Hemolysis Threshold 100 mg/dL
Icterus Threshold 70 mg/dL
Lipemia Threshold 400 mg/dL
Other QNS, contaminated, improperly Labeled, improper specimen type

Specimen Stability

 


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Ambient 8 hours
Refrigerated (4°C to 8°C) 7 days
Frozen(-40°C to 0°C) 12 months

Performance Information

 


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Days and Time Performed 24/7
Expected Turn Around Time Stat: 1 hour
Routine: 4 hours
Stat Availability Yes
Performing Bench UH Chemistry
Methodology/Method Description Roche Cobas – Homogeneous immunoassay based on competition between drug in the specimen and methotrexate labeled with the enzyme glucose-6-phosphate dehydrogenase (G6PDH) for binding to the antibody reagent. As the latter binds antibody, enzyme activity decreases. In the presence of drug from the specimen, enzyme activity increases and is directly proportional to the drug concentration. Active enzyme converts the coenzyme nicotinamide adenine dinucleotide (NAD) to NADH that is measured spectrophotometrically as a rate of change in absorbance. Endogenous serum G6PDH does not interfere with the results becasue the coenzyme NAD functions only with the bacterial enzyme used in the assay.

CPT Codes

80204