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.
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 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.

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