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Serum Carbamazepine Concentration (Trough Level)

Published: August 9, 2026Updated: August 15, 2026

This test measures the amount of carbamazepine, a medication used to treat certain types of seizures or nerve-related conditions, in your blood at a specific time (the trough level). It helps doctors monitor your dose to ensure it’s effective and safe.

Quick summary

["Your doctor may order this test to check if your carbamazepine levels are within the right range for your condition."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 15, 2026Editorial policy

Key facts at a glance

LOINC
97192-9
Short code
CARBT
Synonyms
carBAMazepine Trough SerPl-sCnc
Category
chemistry
Sample
serum
Container
Red-top serum collection tube or serum separator tube (SST)
Units
N/A
Ref low
17
Ref high
51
Critical range
— – 85 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
Immunoassay (e.g., chemiluminescent immunoassay, cloned enzyme donor immunoassay, or particle-enhanced turbidimetric immunoassay); confirmatory methods include liquid chromatography-tandem mass spectrometry (LC-MS/MS) or high-performance liquid chromatography (HPLC)
CPT
80156
SNOMED
395076009
Specimen volume
1-2 mL of serum
Stability
Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 4 weeks. Avoid repeated freeze-thaw cycles.
Hemolysis max
100
Lipemia max
500
Icterus max
25
TAT
4–24 hours
Order
routine

Why This Test Is Done

Doctors may request this test if you’re taking carbamazepine to manage epilepsy, nerve pain, or bipolar disorder. The trough level is taken just before the next dose to assess steady-state blood levels, avoiding peaks and troughs that could affect safety or effectiveness.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into a vein (usually in your arm) to draw a blood sample. The process is quick and usually painless, though you might feel a brief pinch.

What the Results Mean

Results help your doctor determine if your carbamazepine dose is working as intended. Too low levels may mean your medication isn’t strong enough, while too high levels could increase side effects like dizziness or drowsiness. Your doctor will discuss these findings with you.

Common Side Effects or Risks

Carbamazepine can cause side effects like dizziness, drowsiness, or stomach upset. Rarely, it may affect blood cells or cause serious allergic reactions. Always report any unusual symptoms to your healthcare provider.

Reference range

Therapeutic trough range: 17-51 micromol/L (4-12 mg/L). Optimal therapeutic range for most indications is 4-12 mg/L; some references cite 4-10 mg/L for monotherapy and up to 8-12 mg/L for combination therapy.N/A

Specimen: serum

Trough specimen must be drawn immediately before the next scheduled dose, typically in the morning before medication administration. Patient should be at steady-state dosing (usually 2-5 days after initiation or dose change) for accurate interpretation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Carbamazepine Level (Serum)

Frequently asked questions

What problems might this test help detect or manage?
This test helps monitor therapeutic drug levels to prevent toxicity or inadequate response in patients on carbamazepine. It’s particularly important for those with epilepsy or bipolar disorder, as carbamazepine can interact with other medications and may require dose adjustments.
How often should this test be done?
Your doctor will decide the frequency based on your condition, medication regimen, and response. Typically, trough levels are checked every few weeks or months to adjust doses as needed.
Can lifestyle changes affect this test result?
Yes, certain lifestyle factors—like diet, alcohol use, or other medications—can influence carbamazepine levels. Always inform your doctor about all medications, supplements, or changes in your routine before testing.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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