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What is a Carbamazepine test?
Carbamazepine is a drug used for the treatment of seizures (epilepsy), bipolar disorders (to stabilise the mood), alcohol withdrawal (to reduce symptoms of withdrawal) and sometimes in the treatment of neuralgias (nerve pain). A carbamazepine (Tegretol) test is a blood assay that evaluates carbamazepine levels in the bloodstream of patients who are taking the drug. Carbamazepine levels need to be maintained within a therapeutic range. If its levels are low, it may reflect that the drug or its dosage is not effective, which can result in the recurrence of the symptoms; also, extremely high levels of this drug can have toxic effects on the body.

  1. Why is a Carbamazepine test performed?
  2. How do you prepare for a Carbamazepine test?
  3. How is a Carbamazepine test performed?
  4. What do Carbamazepine test results indicate?

A carbamazepine test is performed at a frequent interval from the beginning of the therapy until optimal therapeutic concentrations are attained. Once therapeutic levels are stabilised, the test is performed at longer intervals to ensure that the optimal therapeutic range is being maintained.
However, the test is done every time the symptoms, such as seizures, bipolar mood swings or neuralgias, reappear.
A carbamazepine test is also performed when a person shows symptoms of toxicity or side-effects of the drugs, which may indicate higher levels of carbamazepine in blood. The symptoms of toxicity include

In certain cases, serious side effects can be experienced, which include

  • Paleness of the skin and increased heartbeats along with difficulty in concentrating
  • Ulcers in the mouth and throat
  • Easy bruising or bleeding
  • Tingling sensation and numbness along with muscular weakness
  • Mental confusion, agitation and hallucinations
  • Dyspnoea (difficulty in breathing)
  • Swelling around ankle
  • Yellow discolouration of eyes or skin
  • Severe skin reaction

Usually, no special precautions are required for this test; however, occasionally, the time of intake of the drug is altered.

It is a simple test that takes less than five minutes. An experienced laboratory specialist will withdraw a blood sample from a vein in your arm by inserting a small needle. A small quantity of blood will be collected into a sterile vial or a test tube. You may feel a momentary pricking pain when the needle goes into the vein.
Also, there is a minimal risk of light-headedness and bruising at the site of injection. However, at most times, these symptoms disappear quickly. Rarely, an infection may occur at the site of withdrawal of blood.

Carbamazepine levels are evaluated as micrograms per millilitre (mcg/mL) or expressed as micromoles per litre (micromole/L).

Normal results

Normal or optimal levels of carbamazepine range from 5 to 12 mcg/mL (21.16-50.80 micromole/L).

Abnormal results 

Higher values:

Carbamazepine levels above 15 mcg/mL are considered toxic and can produce symptoms of toxicity, Increased carbamazepine levels can be due to several reasons:

  • Increased absorption of carbamazepine from the gut
  • Prolonged use of the drug (which results in alteration of its metabolism)
  • Alteration of carbamazepine absorption as a side effect of certain other drugs

Lower values:
Lower values of carbamazepine in the blood may result in recurrence of symptoms (such as seizures, bipolar mood disorders or neuralgias). It can be due to:

  • Reduced absorption of carbamazepine from the gut
  • A side effect of certain drugs, leading to reduced carbamazepine absorption
  • Low levels of plasma proteins (especially albumin, which carries carbamazepine)

If carbamazepine test results are in therapeutic range and the person is neither showing symptoms of seizures, mood swings or neuralgia nor experiencing any side effects, it indicates that the dosage of carbamazepine is adequate.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. MedlinePlus Medical Encyclopedia. [Internet] US National Library of Medicine; Carbamazepine
  2. Prasanna A.Datar. Quantitative bioanalytical and analytical method development of dibenzazepine derivative, carbamazepine: A review Journal of Pharmaceutical Analysis, August 2015, Volume 5, Issue 4, Pages 213-222
  3. Robin Ferner. Disposition of toxic drugs and chemicals in man 11th edition Foster City, CA : Biomedical Publications, 2017, Pages 352-54
  4. Patsalos PN. Serum protein binding of 25 antiepileptic drugs in a routine clinical setting: A comparison of free non-protein-bound concentrations. Epilepsia. 2017 Jul;58(7):1234-1243 PMID: 28542801
  5. T B Kudriakova, L A Sirota, G I Rozova, V A Gorkov. Autoinduction and steady-state pharmacokinetics of carbamazepine and its major metabolites Br J Clin Pharmacol. 1992 Jun; 33(6): 611–615 PMID: 1389933
  6. US Food and Drug Administration (FDA) [internet]; Package Inserts – Tegretol (Reference ID: 4236702), Carbatrol (Reference ID: 4312093), Equetro (Reference ID: 3216024)
  7. Yasir Al Khalili, Sameer Jain Carbamazepine Toxicity Carbamazepine Toxicity [Internet]. Treasure Island (FL): StatPearls Publishing
  8. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; Tegretol (Blood)