Urine
Barbiturates
A urine test for barbiturates, such as the epilepsy medicine phenobarbital. For a medical question about the use of sedatives.
€ 53,00
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Metals, toxins and medication · Urine
Barbiturates (urine)
A urine test for barbiturates, an old group of sedatives; in the Netherlands mainly phenobarbital for epilepsy.
At a glance
- Measured in urine
- In 2 test panels
- No special preparation
Explanation
Barbiturates (urine): what is measured?
Barbiturates are sedative and sleep-inducing medicines that used to be prescribed a lot. In the Netherlands, mainly phenobarbital and primidone are still used, two medicines for epilepsy; the body converts primidone into phenobarbital. This screening test is an immunoassay that reacts to the group of barbiturates, with a cut-off of 200 µg/l. The test does not say which medicine was used, nor whether someone is under the influence at this moment.
What can it detect?
- Use of barbiturates, such as phenobarbital, or of primidone, in the past days to weeks
Result
What does the result mean?
Positive result
A positive result means there is a barbiturate in the urine above the laboratory's cut-off. Anyone taking phenobarbital or primidone for epilepsy correctly tests positive. Phenobarbital stays in the body for a long time: according to the Farmacotherapeutisch Kompas, it takes 2 to 6 days for half of it to disappear, so the test can stay positive for a long time after stopping. A positive result shows that a substance is in the body; it is not a diagnosis and says nothing about dependence, the amount or the time of use.
Negative result
A negative result means no barbiturate was found above the cut-off. Short-acting barbiturates leave the body faster than phenobarbital, so use a few days ago can be missed. Other sleeping pills and tranquilizers, such as benzodiazepines, are not detected with this test. Diluted urine from drinking a lot can bring the value below the cut-off.
After an abnormal result
With a positive result that may have consequences, the laboratory has the result confirmed with a second method of analysis that shows which medicine was used. The GP then goes over the medicines of the past weeks.
Reliability
How reliable is the test?
The test says something about use in the past days to weeks, not about health or the extent of use. Because barbiturates are mainly used in the Netherlands as a medicine for epilepsy, a result can only be interpreted if it is known which medicines someone takes. The Dutch Society for Clinical Chemistry (NVKC) states that a positive result of a screening test must be confirmed with a second, different method of analysis; a confirmation test is not included in this test. To assess the dose of phenobarbital, a blood level is needed, not a urine test.
What can affect the result?
- A screening test can give a false-positive result; confirmation with a different method is needed before a result can carry weight.
- Phenobarbital and primidone give a positive result; phenobarbital can remain detectable for a long time after stopping.
- The result says nothing about the blood level and is not suitable for assessing the dose of an epilepsy medicine.
- Fluid intake determines how concentrated the urine is; diluted urine can give a negative result.
Who it is for
Who is the test useful for?
Useful for
Useful for a medical question, for example in addiction care or with unexplained drowsiness in which a sedative may play a role. In people who take phenobarbital or primidone, a positive result adds little; a blood level is needed for the dose.
How common is it?
Barbiturates are rarely used in the Netherlands. As a medicine, it mainly concerns phenobarbital and primidone for epilepsy; recreational use is rare.
Farmacotherapeutisch Kompas
Drawbacks and risks
- A positive result caused by a prescribed epilepsy medicine can wrongly be read as drug use.
- A result without a confirmation test can wrongly be used as evidence.
Get tested
Barbiturates (urine): test panels
Barbiturates (urine) is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
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