Carbamazepine Free Concentration (Serum/Plasma)
This test measures the amount of carbamazepine (an antiseizure medication) that is not bound to proteins in your blood, which can affect how your body uses the drug.
["Understanding your free drug levels helps doctors adjust your dose for better seizure control and fewer side effects."]
Key facts at a glance
- LOINC
- 32852-6
- Short code
- CBZ
- Synonyms
- carBAMazepine free MFr SerPl
- Category
- chemistry
- Sample
- serum
- Container
- Red-top serum tube or serum separator tube (SST)
- Units
- N/A
- Ref low
- 4
- Ref high
- 12
- Critical range
- — – 20 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Immunoassay (e.g., FPIA, chemiluminescence, or LC-MS/MS)
- CPT
- 80156
- SNOMED
- 395076000
- Specimen volume
- 1.0-2.0 mL of serum
- Stability
- Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C): 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 100
- Lipemia max
- 150
- Icterus max
- 50
- TAT
- 4–24 hours
- Order
- routine
Why This Test Matters
Carbamazepine is a medication used to treat certain types of seizures. While the total amount of carbamazepine in your blood is important, doctors also focus on the free (unbound) portion because it’s the part that actually works in your body. Free drug levels can change based on factors like your diet, other medications, or liver function.
How the Test Works
Your blood sample is tested using a method called **immunoassay** (often a type of chemiluminescent or fluorescence-based test). This detects the free, unbound carbamazepine in your serum or plasma, not the protein-bound portion.
What to Expect Before the Test
No special preparation is needed for this test. You may have a small needle inserted into your arm or a fingerstick for a blood sample. If you’re on other medications, tell your healthcare provider—some drugs can affect carbamazepine levels.
Possible Results and Next Steps
Your results will be compared to a general range for free carbamazepine levels, but exact numbers may vary by lab. If your levels are too high or too low, your doctor may adjust your dose or check for interactions with other medications.
Reference range
Therapeutic range for total carbamazepine: 4.0-12.0 mcg/mL; Free carbamazepine therapeutic range: 1.0-3.0 mcg/mL. Reference ranges may vary by laboratory methodology.N/A
No fasting required. Trough levels should be drawn just before the next dose, typically in the morning. Patient should be on a stable dose for at least 5-7 days prior to testing for accurate therapeutic monitoring.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Free Carbamazepine Level
Frequently asked questions
How often should I get this test?
What if my results are outside the normal range?
Can diet or other medications affect 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 14, 2026. · Read our editorial policy