Optimize drug therapy and monitor patient adherence.
Quantitative Enzyme Multiplied Immunoassay Technique
Serum Pre-dose (Trough) Draw - At a Steady State Concentration in Plain Red.
Separate from cells ASAP or within 2 hours of collection. Transfer 2 mL serum to an ARUP Standard Transport Tube. (Min: 1 mL)
Whole Blood, Citrated Plasma. Tubes that contain liquid anticoagulant.or Serum separator tube (SST).
Ambient: 5 days; Refrigerated: 5 days; Frozen: 3 months
Effective November 16, 2015
|Total Carbamazepine||Therapeutic Range: 4.0-12.0 µg/mL
Toxic Range: Greater than 15 µg/mL
|Free Carbamazepine||Therapeutic Range: 1.0-3.0 µg/mL
Toxic Range: Greater than 3.8 µg/mL
|Percent Free Carbamazepine||8.0-35.0%|
The therapeutic range is based on serum pre-dose (trough) draw at steady-state concentration. Free carbamazepine may be important to monitor in patients with altered or unpredictable protein binding capacity. Carbamazepine is also subject to drug-drug interactions due to displacement of protein binding and extensive metabolism. Cross-reactivity with metabolites may account for differences in carbamazepine among analytical methods. Calculating percent free attempts to minimize differences in assay cross-reactivity and may be useful in dose optimization.
A rare adverse drug reaction to carbamazepine therapy includes Stevens-Johnson syndrome or toxic epidermal necrolysis. Patients of Asian ancestry with the presence of the HLA-B*15:02 have an increased risk for this carbamazepine-induced life-threatening reaction. Pharmacogenetic testing for HLA-B*15:02 is recommended for patients at risk for carbamazepine hypersensitivity prior to treatment. This information has been included in the FDA-approved label for carbamazepine (https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&varApplNo=016608) and guideline from the Clinical Pharmacogenetics Implementation Consortium (https://www.pharmgkb.org/guidelines) [ARUP test code 2012049, HLA-B*15:02 Genotyping, Carbamazepine Hypersensitivity.] A combination of therapeutic drug monitoring with HLA-B*15:02 pharmacogenetics genotyping may benefit patients who are at increased risk for developing carbamazepine-induced adverse events due to rare genotypes other than HLA-B*15:02 variant allele.
|Component Test Code*||Component Chart Name||LOINC|
|2011769||Percent Free Carbamazepine||32852-6|
- Carbamazepine, Free
- Free Carbamazepine
- Free Tegretol
- Protein Free Carbamazepine
- Tegretol, Free