Specimen Type/Requirements

Red top (Serum w/out gel) tube - Serum

Do not collect in gel separator tubes.

Sample should be drawn 24 hours after last dose.

Patients who have received glucarpidase (carboxypeptidase G2) as a high dose methotrexate rescue therapy should not be tested with this method.  These patients have an increased level of metabolite that cross reacts with the methotrexate antibody.  These metabolites stay in circulation for 5-7 days.

Test is affected by gross hemolysis.  Test is not affected by lipemia.