Lab Information Manual

Laboratory:

Clinical Biochemistry

Test Name:

METHOTREXATE - (P)

Test Code: MTX

Clinical Information:

Primary testing site: Health Sciences Centre
Secondary testing site: St. Boniface Hospital

Test Indications: Methotrexate is an antineoplastic agent that inhibits DNA synthesis. It is effective in the treatment of neoplastic diseases that have rapid cell proliferation. Methotrexate has the potential for serious toxicity. Testing is used to monitor patients undergoing methotrexate therapy and ensure the drug is being cleared appropriately to avoid toxicity.

Voraxaze (glucarpidase) is a carboxypeptidase enzyme indicated for the treatment of toxic methotrexate concentrations (>1 µmol/L) in patients with delayed methotrexate clearance due to impaired renal function.

However, measurement of methotrexate using immunoassays is unreliable for specimens collected within 48 hours following Voraxaze administration since it can result in falsely elevated results due to crossreactivity with the methotrexate metabolite. As a result, another methodology such as LC-MS/MS assay should be used to monitor methotrexate concentrations postglucarpidase therapy (Send out test) (LINK TO METHOTREXATE POST GLUCARPIDASE- (P))

Collection Devices:

Preferred Device:	1 - Li Heparin, NO GEL 4.0 mL Tube(s) - Full Tube Collection Li Heparin, NO GEL 4.0 mL Tube(s) - Full Tube Collection Manufacturer: BD (Becton Dickinson) Catalogue #: 367884
Alternate Device:	1 - Microtainer(s) - Li Heparin NO GEL (0.4 mL) to fill line Microtainer(s) - Li Heparin NO GEL (0.4 mL) to fill line Manufacturer: Becton Dickinson & Company Catalogue #: 365965

Specimen Required:

Plasma: 0.5 mL

Pediatric Plasma: 0.25 mL

Methotrexate is light sensitive. Protect specimen from light by wrapping with foil or aliquot into a dark transfer vial.
Stability 14 days refrigerated, 1 month frozen

Referral:

Serum: 0.5 mL

Pediatric Serum: 0.25 mL

Methotrexate is light sensitive. Protect specimen from light by wrapping with foil or aliquot into a dark transfer vial.
Samples must be transferred to an aliquot tube and stored frozen if analysis will not be complete within 48 hours (#110-10-05 Serum / Plasma Separation Procedure & Transport)

Requisition:

_SH Biochemistry Hematology Requisition (R250-10-92)

_SH Hospital Biochemistry Hematology Non Winnipeg Brandon (R250-10-91)

_SH Winnipeg Brandon Biochemistry Hematology Requisition (R250-10-94)

_SH Winnipeg Brandon Hospital Biochemistry Hematology Requisition (R250-10-93)

Reference Values:

Limit of quantification for assay is 0.1 μmol/L
Target levels vary depending on the dosage protocol used, but the following generalities can be used:

	24 h	48 h	72 h
Expected Excretion:	< 10 μmol/L	< 1 μmol/L	< 0.1 μmol/L
Mild/Moderate Toxicity:	10-50	1-5	0.5-5
Severe Toxicity:	50-500	5-100	5-50

Availability:

Daily