Leflunomide Metabolite, Serum or Plasma 
Ordering Recommendation

Therapeutic monitoring and evaluating full elimination of the drug (eg, toxicity, pregnancy).

High Performance Liquid Chromatography/Mass Spectrometry
Sun, Wed, Fri
1-6 days
New York DOH Approval Status
This test is New York DOH approved.
Submit With Order
ARUP Consult®
Disease Topics
Specimen Required
Patient Preparation
Timing of specimen collection: Predose (trough). Obtain specimen 12 - 24 hours after last dose. 
Plain red. Also acceptable: Lavender (EDTA), pink (K2EDTA), green (sodium heparin), or gray (sodium fluoride). 
Specimen Preparation
Separate from cells within 2 hours of draw. Transfer 1 mL serum or plasma to an ARUP Standard Transport Tube. (Min: 0.2 mL) 
Storage/Transport Temperature
Refrigerated. Also acceptable: Room temperature or frozen. 
Unacceptable Conditions
Whole blood. Potassium oxalate or separator tubes. 
Ambient: 7 days; Refrigerated: 17 days; Frozen: 90 days 
Reference Interval
Therapeutic RangeGreater than 40.000 µg/mL
Toxic LevelNot well established.

Interpretive Data
Therapeutic and toxic ranges are not well established. Concentrations greater than 40.000 µg/mL tend to correlate with improved patient outcome. A proposed therapeutic range is 50.000 - 100.000 µg/mL. Adverse reactions to Leflunomide, such as diarrhea, hypertension, and liver toxicity, do not correlate well with serum drug concentrations. Leflunomide has a potential risk for teratogenesis. For women being treated with Leflunomide who desire to become pregnant, enhanced drug elimination should be performed until plasma teriflunomide concentrations are lower than 0.020 µg/mL on two separate tests taken at least 14 days apart.

Compliance Statement B: For laboratory developed tests not using a RUO kit, and for FDA approved, cleared or 510(k) exempt assays with alterations. This test was developed and its performance characteristics determined by ARUP Laboratories. The U. S. Food and Drug Administration has not approved or cleared this test; however, FDA clearance or approval is not currently required for clinical use. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions.

Hotline History
Component Test Code*Component Chart NameLOINC
2007461Leflunomide Metabolite, Serum/Plasma44828-2
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.
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