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Leflunomide Metabolite
Test Code18865
CPT Codes
80193
Preferred Specimen
1 mL serum collected in a red-top tube (no gel)
Minimum Volume
0.5 mL
Other Acceptable Specimens
Plasma collected in: Sodium heparin (green-top) or lithium heparin (green-top)
Instructions
Collect specimen in plain red-top tube. Avoid serum separator tubes (SST®).
Transport Container
Plastic screw-cap vial
Transport Temperature
Room temperature
Specimen Stability
Room temperature: 5 days
Refrigerated: 14 days
Frozen: 30 days
Refrigerated: 14 days
Frozen: 30 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Serum separator tubes (SST)
Methodology
Chromatography/Mass Spectrometry
FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by the U.S. Food and Drug Administration. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.
Setup Schedule
Set up: Tues, Thurs, Sat; Report available: 3-5 days
Reference Range
Mean steady state plasma concentrations of teriflunomide from patients on daily dosages of 5, 10, or 25 mg of leflunomide were 8,800, 18,000 and 63,000 ng/mL, respectively. It is recommended that women of childbearing potential who discontinue leflunomide therapy undergo the cholestyramine drug elimination procedure. This procedure includes verification that plasma levels of teriflunomide are less than 20 ng/mL by two separate tests at least 14 days apart.
Clinical Significance
Leflunomide is an immunosuppressant medication used in the treatment of rheumatoid arthritis. Leflunomide is rapidly and extensively metabolized to teriflunomide, which is the active form of the medication. Steady state plasma concentrations in patients receiving recommended daily dosages: up to 63,000 ng/mL. It is recommended that all women of childbearing potential who discontinue leflunomide and women receiving treatment who wish to become pregnant undergo the cholestyramine drug elimination procedure. This procedure includes verification that plasma levels of teriflunomide are less than 20 ng/mL by two separate tests at least 14 days apart.
