Ordering Recommendation

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

New York DOH Approval Status

This test is New York state approved.

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


Liquid Chromatography-Tandem Mass Spectrometry


Sun, Wed, Fri


1-7 days

Reference Interval

Therapeutic Range Greater than 40.000 µg/mL
Toxic Level Not 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.

This test was developed and its performance characteristics determined by ARUP Laboratories. It has not been cleared or approved by the US Food and Drug Administration. This test was performed in a CLIA certified laboratory and is intended for clinical purposes.

Compliance Category

Laboratory Developed Test (LDT)


Hotline History


CPT Codes



Component Test Code* Component Chart Name LOINC
2007461 Leflunomide Metabolite, Serum/Plasma 44828-2
* 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.


  • Arava
  • Arava® (Leflunomide (Teriflunomide), Serum or Plasma)
  • leflunomide blood concentration
  • Teriflunomide
Leflunomide Metabolite, Serum or Plasma