A toxicology screen refers to various tests to determine the type and approximate amount of legal and illegal drugs a person has taken.

Toxicology screening is most often done using a blood or urine sample. However, it may be done soon after swallowing the medication, using stomach contents that are obtained through gastric lavage or after vomiting.

For information on giving a blood sample from a vein, see venipuncture.

For information providing a urine sample, see clean catch urine sample. In some circumstances, you may need to provide the urine sample in the presence of the nurse or technician to verify that the urine sample came from you and was not tampered with.

No special preparation is needed. If able, tell your health care provider what drugs (including over-the-counter medications) you have taken, including when and how much.

This test is sometimes part of an investigation for drug use or abuse. Special consents, handling and labeling of specimens, or other special procedures may be required.

Blood test:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Urine test:

A urine test involves normal urination. There is no discomfort.

This test is often done in emergency medical situations. It can be used to evaluate possible accidental or intentional overdose or poisoning. It may help determine the cause of acute drug toxicity, to monitor drug dependency, and to determine the presence of substances in the body for medical or legal purposes.

Additional reasons the test may be performed:

• Alcoholism
• Alcohol withdrawal state
• Altered mental state
• Analgesic nephropathy
• Complicated alcohol abstinence (delirium tremens)
• Delirium
• Dementia
• Drug abuse monitoring
• Fetal alcohol syndrome
• Intentional overdose
• Seizures
• Stroke secondary to cocaine
• Unconscious patient

If the test is used as a drug screen, it must be done during a certain time period after the drug has been taken or while forms of the drug can still be detected in the body. Examples are below:

• Alcohol: 3 to 10 hours
• Amphetamines: 24 to 48 hours
• Barbiturates: up to 6 weeks
• Benzodiazepines: up to 6 weeks with high level use
• Cocaine: 2 to 4 days; up to 10 to 22 days with heavy use
• Codeine: 1 to 2 days
• Heroin: 1 to 2 days
• Hydromorphone: 1 to 2 days
• Methadone: 2 to 3 days
• Morphine: 1 to 2 days
• Phencyclidine (PCP): 1 to 8 days
• Propoxyphene: 6 to 48 hours
• Tetrahydrocannabinol (THC): 6 to 11 weeks with heavy use

Normal value ranges for over-the-counter or prescription medications may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

A negative value usually means that alcohol, prescription medications that have not been prescribed, and illegal drugs have not been detected.

A blood toxicology screen can determine the presence and level (amount) of a drug in your body.

Urine sample results are usually reported as positive (substance is found) or negative (no substance is found).

Elevated levels of alcohol or prescription drugs can be a sign of intentional or accidental intoxication or overdose.

The presence of illegal drugs or drugs not prescribed for the person indicates illicit drug use.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Commonly found substances on a toxicology screen include:

• Alcohol (ethanol) -- "drinking" alcohol
• Amphetamines
• Antidepressants
• Barbiturates and hypnotics
• Benzodiazepines
• Cocaine
• Marijuana
• Narcotics
• Non-narcotic pain medicines including acetaminophen and anti-inflammatory drugs
• PCP
• Phenothiazines (antipsychotic or tranquilizing medications)
• Prescription medications, any type

Tintinalli JE, Kelen GD, Stapczynski JS, Ma OJ, Cline DM. Toxicology and pharmacology. In: Tintinalli JE, Kelen GD, Stapczynski JS, Ma OJ, Cline DM, eds. Emergency Medicine: A Comprehensive Study Guide. 6th ed. Columbus, OH: McGraw-Hill; 2006:section 14.

McPherson RA, Pincus MR. Toxicology and therapeutic drug monitoring. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 23.