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Blood Test Tracker

Urine Barbiturates Screen

A urine screen for barbiturates, older sedative medicines such as phenobarbital and butalbital. A first positive is presumptive until a second test confirms it.

AI-verified against cited sources. Awaiting expert reviewAlso called BARBLOINC 19270-8

What it is

Barbiturates are sedative drugs. A few are still prescribed, such as phenobarbital for seizures and butalbital in some headache medicines, while most others are rarely used today. The urine screen uses a quick test, called an immunoassay, that reacts to the barbiturate family. It reports only positive or negative against a set cutoff, often 200 or 300 ng/mL. It can't tell which barbiturate is present, how much was taken, or exactly when.

Why it matters

Clinicians order this screen when someone is unusually sleepy or hard to wake, when checking for other drugs taken at the same time, or to see whether a prescribed barbiturate is being taken. Too much of a barbiturate can slow breathing and cause deep sedation. A screen alone can't say whether a dose was a safe prescribed amount, so it is read with symptoms and your medicine list.

If it’s high

A positive screen means the test reacted at or above the lab's cutoff. That is expected if you take a prescribed barbiturate such as phenobarbital, or a medicine that contains butalbital. A confirmation test on the same sample, usually mass spectrometry, can tell which barbiturate is present.

Common causes

  • A prescribed barbiturate, such as phenobarbital, taken as directed
  • A prescription medicine that contains butalbital
  • A medicine that cross-reacts with the test, such as ibuprofen
  • A barbiturate that was not prescribed

What can help

  • Tell the clinician and the lab about every prescription, over-the-counter medicine and supplement you take
  • Ask whether the result was confirmed with a second test, and what cutoff the lab used
  • Ask how long a medicine like phenobarbital is likely to stay detectable in your urine

What can affect your result

  • The cutoff the lab uses (200 or 300 ng/mL)
  • Which barbiturate it is: longer-acting drugs stay detectable longer than short-acting ones
  • How long ago the dose was taken
  • How dilute the urine is
  • Prescription and over-the-counter medicines
  • Prescribed barbiturates, such as phenobarbital, are expected to give a positive screen.
  • Ibuprofen has been reported to cause a false-positive barbiturate screen.
  • Very dilute urine can push a low level under the cutoff and give a negative result.
  • Each lab sets its own cutoff (200 and 300 ng/mL are both used).

Any time. A random urine sample is typical. When results will be used for work or legal reasons, the collection may be observed and the sample temperature checked. Shows recent use. Short- and intermediate-acting barbiturates can be detected for at least 24 to 72 hours, and longer-acting ones for at least 7 days (Labcorp).

When to talk to a clinician

A positive screen alone is not an emergency. Call 911 or your local emergency number if someone is extremely sleepy or can't be woken, is breathing slowly or shallowly, or is confused after taking a sedative. In the US, Poison Control is 1-800-222-1222.

Questions you could ask

  • Who will see this result, and how will it be used?
  • Could one of my medicines explain this result?
  • Was this result confirmed with a second, more specific test?
  • What cutoff did this lab use?

Questions people ask

Will my phenobarbital show up?

Yes. Phenobarbital is one of the barbiturates this screen is built to find, so a positive result is expected if you take it. Tell the clinician and the lab.

How long can a barbiturate be detected in urine?

Labcorp states that short- and intermediate-acting barbiturates can be detected for at least 24 to 72 hours, and longer-acting ones for at least seven days. Your dose and how often you take it also matter.

Can a common pain reliever cause a false positive?

Ibuprofen has been reported to cause a positive barbiturate screen. A confirmation test on the same sample can tell a false positive from a true one.

Show the science and sources

For clinicians and researchers

Barbiturate immunoassays detect the class through cross-reactivity with a calibrator. Labcorp states that urine is presumptively positive above 300 ng/mL using secobarbital as the standard, and that short- and intermediate-acting barbiturates can be detected for at least 24 to 72 hours after ingestion and longer-acting drugs for at least seven days. Mayo Clinic Laboratories reports a barbiturate immunoassay with a 200 ng/mL screening cutoff (LOINC 70155-7) and confirms positives by GC-MS, and a hospital device in a 2025 report also used 200 ng/mL. LOINC has separate screen codes for 200 and 300 ng/mL. Labcorp's confirmation covers amobarbital, butalbital, pentobarbital, phenobarbital and secobarbital. Barbiturates have a narrow therapeutic index, and toxicity ranges from sedation to coma, respiratory depression and hypotension (StatPearls). Merck Manual gives ibuprofen as an example of a cross-reacting drug on the barbiturate screen. Immunoassay positives are presumptive until a second independent method confirms them (Saitman 2014). Urine testing cannot determine the amount or frequency of use (Merck Manual).

LOINC 19270-8 (primary), 70155-7, 70139-1, 3377-9. Specimen: urine.

Sources

  1. Drug Testing, Merck Manual Professional Version (2026)
  2. Drug Testing, MedlinePlus (National Library of Medicine)
  3. Commonly prescribed medications and potential false-positive urine drug screens, American Journal of Health-System Pharmacy (2010)
  4. False-positive interferences of common urine drug screen immunoassays: a review, Journal of Analytical Toxicology (2014)
  5. Abnormal Urine Drug Screens in Pregnancy: Opportunity for Laboratory Stewardship, EJIFCC (IFCC) (2025)
  6. Barbiturates, Screen and Confirmation, Urine (test 074419), Labcorp
  7. CSMPU: Controlled Substance Monitoring Profile, Random, Urine, Mayo Clinic Laboratories Extended Catalog
  8. Barbiturate Toxicity, StatPearls Publishing (NCBI Bookshelf) (2024)
  9. Butalbital, Acetaminophen and Caffeine tablet (drug label), DailyMed (National Library of Medicine)
  10. Contact us - Poison Control, Poison Control (America's Poison Centers)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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