Serum Free Carbamazepine Concentration
This test measures the amount of carbamazepine (an anticonvulsant medication) that is not bound to proteins in your blood, helping doctors monitor your drug levels for optimal safety and effectiveness.
["Your free carbamazepine level helps ensure your medication is working as intended without causing harmful side effects."]
Key facts at a glance
- LOINC
- 32058-0
- Short code
- CARBFR
- Synonyms
- carBAMazepine free SerPl-sCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red top tube (serum) or serum separator tube (SST); avoid gel-based tubes for free drug measurement
- Units
- N/A
- Ref low
- 4.2
- Ref high
- 12.7
- Critical range
- — – 25.4 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Immunoassay (e.g., cloned enzyme donor immunoassay [CEDIA], fluorescence polarization immunoassay [FPIA], or chemiluminescent immunoassay [CLIA])
- CPT
- 80157
- SNOMED
- 396080003
- Specimen volume
- 1-2 mL of serum (minimum 0.5 mL)
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C): 30 days. For free fraction analysis, separate serum promptly and store frozen if not analyzed within 24 hours.
- Hemolysis max
- 100
- Lipemia max
- 200
- Icterus max
- 25
- TAT
- 4–24 hours
- Order
- routine
Why This Test Matters
Carbamazepine is used to treat seizures and some types of nerve pain. While the total blood level of carbamazepine is important, measuring the free (unbound) portion provides a more accurate picture of how much of the drug is actually available to work in your body. This can help prevent toxicity or insufficient dosing.
What to Expect Before the Test
No special preparation is needed for this test. You may have a small needle inserted into a vein in your arm, or a blood sample may be collected from a finger prick. The process is quick and usually painless.
How the Results Are Used
Your healthcare provider will use these results to adjust your carbamazepine dose if needed. Free levels can be particularly useful when monitoring patients with liver issues, kidney problems, or those taking medications that affect protein binding.
Common Reasons for Testing
This test is often ordered if you’re on carbamazepine to manage seizures or pain, or if your doctor suspects your medication levels are too high or too low. It may also be used to check for interactions with other medications that alter protein binding.
Reference range
Therapeutic free carbamazepine concentration: 1.0-3.0 mg/L (4.2-12.7 µmol/L); free fraction typically 20-25% of total concentrationN/A
No fasting required. Trough levels should be drawn immediately before the next scheduled dose, typically 8-12 hours after the last dose, to ensure consistent drug monitoring. Patients should be on a stable dose for at least 5-7 days before sampling.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Free Carbamazepine Level
Frequently asked questions
What does a high or low free carbamazepine level mean?
How often should I get this test?
Can I drink water before this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 15, 2026. · Read our editorial policy