At a Glance
Why Get Tested?
To determine the concentration of carbamazepine in the blood to establish an appropriate dose and maintain a therapeutic level
When to Get Tested?
At regular intervals to monitor the drug's level; when indicated to detect low or excessive (potentially toxic) concentrations
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
Carbamazepine is a drug that is primarily used to treat certain seizure disorders (also called epilepsy) but is also prescribed to stabilize the moods of people with bipolar disease and to help alleviate some types of nerve pain. It may be prescribed by itself or in combination with other antiepileptic drugs. This test measures the amount of carbamazepine in the blood.
Carbamazepine levels are monitored because the drug must be maintained within a narrow therapeutic range. If the level is too low, the person may experience a recurrence of symptoms (i.e., seizures, mania, or pain); if the level is too high, the person may experience toxic side effects. Maintaining a therapeutic level of the drug can be a challenge to achieve for several different reasons:
- Oral doses of carbamazepine are absorbed in the gastrointestinal tract at widely variable rates.
- Since carbamazepine is metabolized by the liver, anything that affects liver function can affect blood levels of the drug.
- Much of the drug is bound to plasma protein, but it is the free portion of the drug that is active. Conditions that affect protein binding of the drug may affect therapeutic effectiveness. This may occur when someone has low blood albumin, kidney failure, or when they are very young (newborn) or elderly.
- The metabolite of carbamazepine, carbamazepine-10 11 epoxide, is also active and contributes to the overall effect of the medication.
- Several drugs, if taken in conjunction with carbamazepine, may interact or affect metabolism and blood levels.
Dosages of carbamazepine must be adjusted carefully until a steady concentration in the blood is reached. The actual amount of drug that it takes to reach this steady state will vary from person to person and may change over time.
Carbamazepine is usually monitored long-term because it is prescribed to treat the chronic conditions epilepsy, bipolar disorder, or trigeminal neuralgia.
Epilepsy affects the brain's ability to transmit electrical impulses and to regulate nerve activity. During a seizure, a person may experience changes in consciousness, alterations in sight, smell, and taste, and may experience convulsions. The frequency of seizures varies from a single episode, to occasional seizures, to recurrent seizures. Seizures are categorized by the parts of the brain and body that are affected. Carbamazepine is prescribed to help prevent specific types of recurrent seizures.
Bipolar disorder is a mental condition that is characterized by cycles of depression and mania that may last for days, weeks, months, or years. During a depressive episode, those affected may feel sad, hopeless, worthless, and have thoughts of suicide. During a manic episode, those affected may be euphoric, irritable, use poor judgment, and participate in risky behaviors. Carbamazepine is prescribed to help even out the moods of the person with bipolar disorder, especially mania.
Trigeminal neuralgia, a condition associated with facial nerve pain and muscle spasms, and paroxysmal choreoathetosis are also sometimes treated with carbamazepine.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. St. Louis: Elsevier Saunders; 2006, Pp1249-1250, 2305.
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC., Pg 461, 456.
Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Pg 313.
(Sep 1, 2009) MedlinePlus Medical Encyclopedia. Drug Information, Carbamazepine. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/meds/a682237.html. Accessed Nov 2011.
(Jan 25, 2010) U.S. Food and Drug Administration. Information on Carbamazepine (marketed as Carbatrol, Equetro, Tegretol, and generics) with FDA Alerts. Available online through http://www.fda.gov. Accessed 2011.
Sources Used in Previous Reviews
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Pp 461.
Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 1284-1285.
Rosenbaum, J. and Covino, J. (2007 September 24). Observations on the Treatment of Bipolar Disorder. Medscape Psychiatry & Mental Health [On-line information]. Available online at http://www.medscape.com/viewarticle/563043 through http://www.medscape.com. Accessed on 11/11/07.
(2007 May 1). Carbamazepine. MedlinePlus Drug Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682237.html. Accessed on 11/7/07.
(2003 February, Revised). Seizure Disorders. Merck Manual of Medical Information – Second Home Edition [On-line information]. Available online at http://www.merck.com/mmhe/sec06/ch085/ch085a.html through http://www.merck.com. Accessed on 11/7/07.
(2007). ACPA Medications & Chronic Pain Supplement 2007. ACPA [On-line information]. PDF available for download through http://www.theacpa.org. Accessed on 11/11/07.
Szabo, C. A. (2007 November 7). Risk of fetal death and malformation related to seizure medications. Neurology 2006;67;6-7 [On-line journal]. Available online at http://www.neurology.org/cgi/content/full/67/3/E6 through http://www.neurology.org. Accessed on 11/11/07.
Pregnancy Issues. Epilepsy Foundation [On-line information]. Available online at http://www.epilepsyfoundation.org/living/women/pregnancy/weipregnancy.cfm through http://www.epilepsyfoundation.org. Accessed on 11/11/07.
(2007 February 14). NINDS Paroxysmal Choreoathetosis Information Page. NINDS [On-line information]. Available online through http://www.ninds.nih.gov. Accessed on 11/7/07.
Spearing, M. (2007 January, Updated). Bipolar Disorder. National Institute of Mental Health [On-line information]. Available online through http://www.nimh.nih.gov. Accessed on 11/11/07.
(© 2007). Carbamazepine, Free & Total. ARUP’s Laboratory Test Directory [On-line information]. Available online at http://www.aruplab.com/guides/ug/tests/0090615.jsp through http://www.aruplab.com. Accessed on 11/10/07.
(© 2007). Carbamazepine (Tegretol®), Serum. LabCorp [On-line information]. Available online at http://www.labcorp.com/datasets/labcorp/html/chapter/ through http://www.labcorp.com. Accessed on 11/10/07.
(© 2007). Carbamazepine-10,11 Epoxide. LabCorp [On-line information]. Available online at http://www.labcorp.com/datasets/labcorp/html/chapter/ through http://www.labcorp.com. Accessed on 11/10/07.
(© 2007). Carbamazepine, Epoxide & Total. ARUP’s Laboratory Test Directory [On-line information]. Available online at http://www.aruplab.com/guides/ug/tests/0092211.jsp through http://www.aruplab.com. Accessed on 11/10/07.
Carbamazepine Oral. Medscape Drug Information, Doses, Usage, and Warnings. [On-line information]. Available online through http://www.medscape.com. Accessed on 11/11/07.
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Kapoor, N. and Hamilton, R. (2007 April 27). Toxicity, Carbamazepine. emedicine [On-line information]. Available online at http://www.emedicine.com/emerg/TOPIC77.HTM through http://www.emedicine.com. Accessed on 11/11/07.
Bakerman's ABC's of Interpretive Laboratory Data, Fourth Edition, Seymour Bakerman, M.D., Ph.D., 2002. Accessed online, December 2007 at http://www.bakermanbooks.com.
(December 12, 2007) FDA News. Carbamazepine Prescribing Information to Include Recommendation of Genetic Test for Patients with Asian Ancestry, Connection of genetic information with medication use can improve safe use of product (online information, accessed December 2007). Available onliine at http://www.fda.gov/bbs/topics/NEWS/2007/NEW01755.html through http://www.fda.gov.
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