Toxicology Screen

Written by Dale Kiefer | Published on July 25, 2012
Medically Reviewed by Brenda B. Spriggs, MD, MPH, FACP


A toxicology screen is a test used to determine if an individual has been exposed to certain legal or illegal drugs. Toxicology screens are usually ordered to see if a patient has taken drugs that could endanger his or her health. If a patient is suspected of taking illegal drugs, a screen for specific drugs that are commonly abused may be ordered.

Toxicology screens are often ordered by hospital emergency department personnel when a patient appears to be impaired or is unconscious. Testing is also done in patients who have a change in mental status, in cases of seizures, and onset of dementia. Toxicology testing can also be useful in cases of suspected sexual assault.

In some cases, a patient may have been exposed to a prescription drug accidentally or overdose may be suspected. Some employers require random drug screening. Employees who test positive for illegal drug abuse may be suspended or fired.

The test can be performed fairly quickly. Results can help doctors treat the patient effectively and safely.

Types of Toxicology Screens

There are several types of toxicology screens. Most screening methods use a sample of urine to test for the presence of illegal narcotics or prescription drugs. Some, like the blood alcohol test, can determine the precise concentration of a particular drug. Others, like the urine screen, can indicate if a person has been exposed to drugs or poisons. Drug screens can also be performed on saliva.

One common type of toxicology test looks for evidence of alcohol abuse by a mother during pregnancy. Her newborn’s first stool is examined to predict a condition called fetal alcohol syndrome.

Most screens provide limited information about how much or how often a patient has taken a drug. Once the presence of a drug has been identified by screening, the doctor may order a more specific test, which will show exactly how much of the drug is present in the patient’s system.

The contents of the stomach may also be screened when doctors suspect a patient may have taken a drug orally.

How Samples for Toxicology Screens Are Obtained

Some toxicology screens are obtained by doing blood tests, which involve drawing one or more small tubes of blood. A medical professional inserts a needle into a vein and removes enough blood to perform the necessary tests.

If a urine sample is required, the patient may be asked to urinate into a small sample cup in the presence of law enforcement or medical personnel. This prevents the patient from tampering with the sample.

Types of Drugs Screened

Many types of drugs can be identified by toxicology screens. Depending on the drug, it may show up in the blood or urine hours or weeks after exposure to the drug. For example, alcohol is eliminated from the body relatively rapidly. It’s necessary to draw blood within about three hours of an automobile accident to accurately reflect a patient’s blood alcohol status at the time of the incident.

Other drugs, such as THC, a component of marijuana, may show up in urine for months after exposure. How long THC remains detectable depends on whether the patient is a heavy user.

Common classes of drugs that may be detected by toxicology screens include:

  • alcohol (including ethanol and methanol)
  • amphetamines (such as Adderall)
  • barbiturates
  • benzodiazepines
  • methadone
  • cocaine
  • opiates (including codeine, oxycodone, heroin)
  • phencyclidine (PCP)
  • tetrahydrocannabinol (THC)
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Show Sources

  • Lund HM, Øiestad EL, et al. Drugs of abuse in oral fluid collected by two different sample kits--stability testing and validation using ultra performance tandem mass spectrometry analysis. 2011 J Chromatogr B Analyt Technol Biomed Life Sci. Nov 15;879(30):3367-77. Epub 2011 Sep 9.
  • Markway EC, Baker SN. A review of the methods, interpretation, and limitations of the urine drug screen. 2011 Orthopedics. Nov;34(11):877-81.
  • Mueller DM, Rentsch KM. Online extraction toxicological MS(n) screening system for serum and heparinized plasma and comparison of screening results between plasma and urine in the context of clinical data. 2012 J Chromatogr B Analyt Technol Biomed Life Sci. Feb 1;883-884:189-97. Epub 2011 Aug 24.
  • Toxicology screen: MedlinePlus. (n.d.). National Library of Medicine - National Institutes of Health. Retrieved May 17, 2012, from
  • Zelner I, Shor S, et al. Neonatal screening for prenatal alcohol exposure: Assessment of voluntary maternal participation in an open meconium screening program. 2012 Alcohol. May;46(3):269-76. Epub 2012 Mar 21.

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