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Test Code MX Methotrexate Level

Specimen Type

Blood

Container

Red top – Protect from light

Preferred Volume

4 mL

Offsite Collection Instructions

Wrap specimen in foil to protect from exposure to light.
Pharmacokinetic factors influence the correct time of sample collection after the last drug dose. These factors include dosage form, mode of administration, concomitant drug therapy, and biological variations affecting drug disposition.

UCMC Collection Instructions

Wrap specimen in foil to protect from exposure to light.
Pharmacokinetic factors influence the correct time of sample collection after the last drug dose. These factors include dosage form, mode of administration, concomitant drug therapy, and biological variations affecting drug disposition.
Low dose therapy:  Q weekly
High dose therapy:  24hr, 48hr, 72hr

Availability

24/7

Turnaround Time

3 hours

STAT Availability

Not Available

Test Methodology

Enzyme multiplied immunoassay technique (EMIT)

Additional Information

The concentration of methotrexate in serum or plasma depends on the time of the last drug dose; mode of administration; concomitant drug therapy; sample condition; time of sample collection; and individual variations in absorption, distribution, biotransformation, and excretion. These parameters must be considered when interpreting results.

CPT Code

80299

Test Includes

quantitative determination of methotrexate in serum

Critical Results

None

Test Limitations

Aminopterin, an antineoplastic agent not usually administered concurrently with methotrexate, and 4-amino-4-deoxy-N10-methylpteroic acid (APA), a minor metabolite of methotrexate, cross-react significantly with this assay.

Reference Range

Subject to interpretation by ordering physician.

24 hr post high dose: > 5 umol/L
48 hr post high dose: > 0.5 umol/L
72 hr post high does: > 0.1 umol/L

Reference:
Cadman EC, Durivage HJ: Cancer chemotherapy: alkylating agents. In Harrison’s Principles of Internal Medicine. 12th edition. Edited by JD Wilson, E Braunwald, KJ Isselbacher, et al. New York, McGraw-Hill Book Company, 1991, pp 1592-1594

Minimum Volume

2 mL

Fee Code

43639