What is the Carbamazepine test?

Frequently Asked Questions:

What is the Carbamazepine Test used for?

There are many uses for the test, the primary among them is to monitor carbamazepine levels in your blood. This is imperative as carbamazepine has a low therapeutic drug range(TDR). Even a slight, often undetectable change in its levels could lead to problems in long-term use. The dosage must be maintained within a relatively narrow concentration range. 

If the level is too low, the treatment could fail and the symptoms may recur. If the level is too high, the patient may experience increased toxic and adverse effects of the drug. 

Why do I need the Carbamazepine Test?

Your physician may request this test before and during your treatment to monitor its bloodstream levels. This test may not be required once the drug has attained a stable concentration in your body over the period of treatment. 

You may also be required to take the test for other reasons: to check the effectiveness of the drug in your treatment, to rule out sensitivity to the drug or in case you experience severe side effects to the drug.

When should I test my carbamazepine levels?

The test should be carried out upon request by your physician. Some common symptoms indicating the need to get tested include: 

• Suicidal thoughts
• Uncoordinated movements
• Difficulty sleeping or excessive sleepiness
• Dry mouth
• Nystagmus - or involuntary movements of the eyeball
• Severe blood reactions

What happens during the Carbamazepine Test?

The Carbamazepine Test is a simple blood test wherein a blood sample is taken from your vein. The procedure takes only a few minutes. The sample is then sent to the lab for testing to find the level of carbamazepine in your bloodstream.

Will I need to do anything to prepare for the test?

No, there are no prerequisites for the test. However, letting your physician know about medicines, supplements, or substances you’ve been taking is important because some of these can alter the test results. 

These include over-the-counter medications such as paracetamol, warfarin, rifampicin, erythromycin, estrogen, oral contraceptives and immunosuppressant drugs. Higher levels could be due to concurrent use of other antiepileptic drugs too.

Are there any risks to the test?

Like every other test that involves a needle, this also carries certain risks that include bleeding, infection, bruising, or dizziness. A sensation of pain may be felt when the needle pricks your arm, and the site may be slightly sore for a while.

Understanding the test results of the Carbamazepine Test

• The test results are in milligrams per litre of blood
• A therapeutic range of carbamazepine is 4-12 mg/L indicates an optimum level in the blood
• The minimum toxic level is 10 mg/kg
• A toxic clinical value greater than 30-40 mg/L indicates toxicity

Your test results may not always indicate a problem, so it is imperative that you follow your physician’s advice regarding the altered levels.

How long does carbamazepine stay in your system?

This is measured by the half-life of a drug; when the drug reaches 50% of its concentration in the bloodstream.

Carbamazepine stays in the system for 5-26 hours for long-term use (3-5 weeks of continuous drug therapy). For short-term use, the half-life of carbamazepine is 18-55 hours. It leaves your body after approximately four days or 93.5 hours.

Can carbamazepine be started without genetic testing?

A genetic segment is called an allele. Specifically, the allele HLA-B*1502 increases the risk of blood and related side effects. This is especially true for a severe condition called the Stevens-Johnson Syndrome that affects the Asian population in particular. However, prior genetic testing is NOT mandatory to initiate carbamazepine therapy.

Does carbamazepine need to be tapered?

Yes. It would be best if you don’t stop carbamazepine suddenly and abruptly. It can cause an exaggeration of your symptoms, even if you feel your symptoms have disappeared. Kindly contact your physician to indicate the tapering and gradual discontinuation. 

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