Carbamazepine (Tegretol) Test

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

• Dizziness
• Uncontrolled movements
• Excessive sleepiness (alteration of the sleep cycle)
• Blurring of vision or diplopia (double vision)
• Involuntary movement of the eyeball (nystagmus)
• Nausea
• Diarrhoea
• Red and itchy rashes on the skin (Read more: Skin rashes causes)
• Constipation
• Headache
• Confusion

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.