Primus Pathology Laboratory

Carbamazepine Test

Last Updated on August 1, 2022 by Dr. Neeraj Gujar

Carbamazepine Test

Cautionary Note: Please note that Carbamazepine Medication should not be stopped or dosage changed without first consulting with your healthcare provider. Any self-medication or self-alteration of dosage may cause adverse effects.


Carbamazepine is a drug used to treat seizure disorders (like epilepsy). It can also be prescribed to stabilize moods, ease alcohol withdrawal, and relieve some types of nerve pain. It is either prescribed by itself or it is combined with other antiepileptic medications. This test measures carbamazepine levels in the blood.

The drug has a limited therapeutic range and so it is important to monitor its levels. The drug can cause side effects such as seizures, mania, or paralysis. If the levels are too low, it may not work properly. It can be difficult to maintain a therapeutic dose of this drug for many reasons.

  • Carbamazepine oral doses are absorbed by the gastrointestinal tract at varying rates.
  • Carbamazepine can be induced to its metabolism by long-term administration.
  • Carbamazepine metabolism is controlled by the liver. Any impairment in liver function could affect blood levels.
  • Most of the drug is bound by plasma protein and only the free portion is active. Therapeutic effectiveness may be affected by conditions that alter this protein binding ability. This can happen when someone is very young, has kidney disease, or low albumin level.
  • The metabolite of carbamazepine i.e. carbamazepine-10,11-epoxide is also therapeutically active and contributes to the overall effect of the medication.
  • If taken with other drugs, they may interact or alter carbamazepine’s metabolism and blood levels.

To maintain a steady blood concentration, carbamazepine doses must be adjusted. This steady-state may require a different amount of drug depending on the individual. This can change with time.

Carbamazepine should be monitored for the long term as it is prescribed to treat chronic conditions such as epilepsy, bipolar disorder trigeminal neuralgia, and nerve pain due to diabetes.

Epilepsy is a condition that affects the brain’s ability to transmit electrical impulses and regulate nerve activity. A seizure can cause changes in consciousness, altered sight, smell, taste, and convulsions. There are many types of seizures. They can be brief, frequent, occasional, or recurrent. Carbamazepine can be prescribed to prevent certain types of recurrent seizures.

Bipolar disorder refers to a mental condition marked by periods of depression or mania lasting for days, weeks, and months. A depressive episode can cause depression and make people feel hopeless, worthless, sad, or even suicidal. A manic episode can cause euphoria, irritability, poor judgment, and risky behavior. Carbamazepine, which is used to treat bipolar disorder, helps with mania and other mood swings.

Carbamazepine can also be used to treat trigeminal nerve pain, which is a condition that causes facial nerve pain and muscle spasms. Paroxysmal choreoathetosis is a movement disorder that causes involuntary movements and limb movements. 

The diabetic peripheral neuropathy pain affects the function, mood, sleep patterns, and functionality of about 10-20% of patients with diabetes mellitus.

Why Carbamazepine Test Is Done?

Carbamazepine testing is used to monitor and measure the amount of carbamazepine present in the blood. This is done to determine the drug’s therapeutic level. The test can be used to determine the right dose for the individual. The blood test results may allow for adjustments to the drug dose until it reaches the therapeutic level. The level is then checked with subsequent tests. The test can be used to determine if an adjustment to the prescribed dosage is required if a person’s condition changes.

To help someone suffering side effects, adverse reactions, or recurrences of symptoms, a healthcare practitioner might use carbamazepine testing.

A routine carbamazepine testing measures total carbamazepine. This includes both the protein-bound as well as free portions. Sometimes a test to measure free carbamazepine or the biologically active metabolite (carbamazepine-10,11-epoxide) is ordered along with the total carbamazepine test to evaluate their contribution to a person’s therapy.

Also Read: Everything About a Blood Test

When To Get Tested?

Carbamazepine blood tests are ordered often at first. Then, at regular intervals and as necessary to maintain therapeutic blood levels.

If the dosage of the drug is changed or the person being treated starts or stops taking other medications, additional total carbamazepine testing may be required to determine if they have any effect on the carbamazepine levels. To ensure that blood levels of carbamazepine remain within the therapeutic range, they are continuously monitored.

A carbamazepine testing may be requested if a person is not responding to therapy or has a recurrence of symptoms like seizure, nerve pain, and bipolar mood swings. It is possible that the blood level is not high enough. The person might not be taking the medication regularly or the drug may not work for them.

If a person is experiencing troublesome side effects or complications, Carbamazepine testing may be ordered. Side effects can occur at any dose, but are more familiar with higher concentrations.

  • Dizziness
  • Sleepiness
  • Confusion
  • Double vision or blurred vision
  • Itchy, red rash
  • Nausea
  • Diarrhea
  • Constipation
  • Headache

If someone experiences serious side effects, such as:

  • Pale skin, rapid heart rate, trouble concentrating
  • Severe skin reaction
  • Chills, fever, or sore throat
  • Bleeding or bruising easily
  • Lung and throat infections
  • Confusion, agitation, or hallucinations can occur due to vision problems, confusion, or agitation.
  • Breathing difficulties
  • Severe tingling, numbness, pain, muscle weakness
  • The swelling of the feet or ankles
  • You urinate less often than you would normally
  • Eyes or skin yellowing

Carbamazepine may also cause liver dysfunction, low salt levels, decreased white cells, and an increase in eosinophils, which is a type of white blood cell. Some side effects can be so severe that it is necessary to use a different anti-seizure or bipolar medication.

A free carbamazepine test and/or a carbamazepine-10,11-epoxide test may also be ordered along with the total carbamazepine test when a health care practitioner wants to evaluate the contribution of the free drug and/or its metabolite to drug therapy. If the results of a total carbamazepine testing are within the therapeutic range, but the patient suffers from side effects, the healthcare practitioner might opt to order this test. Sometimes, results can be compared to determine the percentage of total or free carbamazepine.

How To Get Tested?

No special preparation is required for this test. It is a simple blood test wherein a sample of blood is drawn from the vein in your arm.

Also Read: 4 Blood Tests to Assess Your Heart Health

Test Results

Carbamazepine’s therapeutic range is approximately 4-12 mcg/mL when taken as an individual. Toxic levels are those above 15 mg/mL. The ranges may vary from one laboratory to another, but they can be expressed in other units, such as mg/L (milligrams/liter). The laboratory performing the testing should provide the appropriate therapeutic ranges and units for patients and health care professionals.

Most people will experience side effects within the therapeutic range. However, each person’s response to the drug is different. Some people may experience side effects such as mood swings or seizures at the lower end of the therapeutic range, while others will experience severe side effects at higher levels. Variations in free carbamazepine and carbamazepine-10,11-epoxide can contribute to this response. This medication is best used by people who are in close contact with health care providers.

If carbamazepine tests are within the therapeutic range, and the person being treated is not having recurrent seizures or mood swings, or nerve pain, then the dosage of carbamazepine should be considered adequate.

Patients should consult their doctor before increasing, decreasing, or stopping taking their medication. This can increase the chance of having seizures and could also affect other medications. Each case must be assessed individually when determining dosage and making adjustments.

Also Read: Renal Function Test


How long does it take for carbamazepine to completely leave your body?

The elimination half-life of carbamazepine is 35 hours on a single oral dose. In the case of multiple dosing, the half-life decreases.

What is one thing that patients taking carbamazepine must know?

Carbamazepine interacts with various drugs. Many prescription medications can interact with carbamazepine. These include commonly prescribed medicines, such as warfarin, antidepressants, fluoxetine, ethosuximide, and erythromycin. Carbamazepine may also interact with or affect over-the-counter medicines such as acetaminophen, as well as herbal supplements like St. John’s wort. Grapefruit juice may increase blood levels of carbamazepine. So, people should always inform their healthcare providers about any prescription drugs, over-the-counter medicines, or herbal supplements they are taking

What length of time will I be taking carbamazepine for?

Patients with epilepsy, bipolar disorder, chronic nerve pain, and other conditions will often take carbamazepine throughout their lives. The person may have to switch to another drug if carbamazepine becomes ineffective or has adverse side effects. A person with temporary seizures may only require the medication for a brief time.

Will my doctor order free carbamazepine or carbamazepine-10,11-epoxide frequently?

Generally, no. You will not need to have these additional tests performed routinely. However, they may be ordered a few times to assess how your body is metabolizing carbamazepine.

by Dr. Neeraj Gujar

Dr. Neeraj Gujar has done his M.D. in Pathology from Government Medical College. He has worked at various organisations such as Breach Candy Hospital and Tata Memorial Hospital along with many other private organisations. During his working career, he realised the pressing need for exceptional quality diagnostic services. A diagnostic centre that can consistently give accurate results verified by a consultant doctor (M.D. Pathologist) on which your doctor can depend. This has been the founding principle of Primus Pathology and Diagnostics.

Leave a Reply

Your email address will not be published. Required fields are marked *