Metals, toxins and medication
Barbituraten
A urine test for barbiturates, an old group of sedatives; in the Netherlands mainly phenobarbital for epilepsy.
Everything about this testWhat it measures
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.
- Use of barbiturates, such as phenobarbital, or of primidone, in the past days to weeks
Positive
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
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.
If your result is abnormal
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
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.
Limitations
- 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.
How common is this
Barbiturates are rarely used in the Netherlands. As a medicine, it mainly concerns phenobarbital and primidone for epilepsy; recreational use is rare.
Who is this 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.
Downsides 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.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results