Lab Test

Carbamazepine Level, Unbound (including Total)

Tegretol, Carbamazepine, Unbound

Test Codes

Antrim #19135, EPIC: LAB5381, SOFT: CARBU



Specimen Collection Criteria

Collect: One plain Red-top tube. (Minimum Whole Blood: 3.0 mL)

Do not use Serum Separator Tubes.
Time of Collection:
Trough, just prior to the next dose.
Record the exact time of specimen collection on the tube or in the computer system.

Physician Office/Draw Specimen Preparation

Let specimens clot 30-60 minutes. Refrigerate (2-8°C or 36-46°F) the collection tube within two hours of collection. (Minimum: 3.0 mL blood)

Preparation for Courier Transport

Transport: Collection tube, refrigerated (2-8°C or 36-46°F). (Minimum: 3.0 mL blood)

Rejection Criteria

  • Serum Separator (SST) tubes.
  • Severely lipemic or hemolyzed specimens.  

In-Lab Processing

Let specimens clot 30-60 minutes. Centrifuge specimen to separate serum from cells. Deliver an aliquot of serum or the collection tube immediately to the appropriate testing station.


Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 24 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 3 months

Specimen Storage in Department Prior to Disposal:

Frozen (-20°C/-4°F or below): 2 months


Royal Oak Toxicology Laboratory


Sunday – Saturday.
Results are available within 24 hours.

Reference Range

Free Carbamazepine: 1.5-3.0 mcg/mL.
Total Carbamazepine: 6.0-12.0 mcg/mL.
% Free Carbamazepine: 25.0% +/- 5%.
Critical Value: Greater than 5.0 mcg/mL.

Test Methodology

Total Carbamazepine: Particle Enhanced Turbidimetric Inhibition Immunoassay. Unbound Carbamazepine: Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). 

The free carbamazepine portion of this test was developed and its performance characteristics determined by Beaumont Health. It has not been cleared or approved by the FDA. The Laboratory is regulated under CLIA as qualified to perform high-complexity testing. This test is used for clinical purposes and should not be regarded as investigational or for research.


This method measures both the total and unbound concentrations of carbamazepine. The unbound concentration of carbamazepine is thought to be most closely associated with therapeutic effect and toxicity.

Carbamazepine is bound to albumin and alpha-1-acid-glycoprotein. Changes in free fraction will cause corresponding changes in carbamezepine clearance and total carbamezepine concentration. Unbound concentrations are considered to be independent of binding changes.

Clinical Utility

Carbamazepine is used to control partial seizures with both temporal lobe and psychomotor symptoms and for generalized tonic-clonic seizures. This assay is used to monitor the therapeutic drug level and extent of serum protein binding.

CPT Codes

LOINC: 3432-2, 3433-0


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