Toxicology screen

Definition

A toxicology screen refers to various tests that determine the type and approximate amount of legal and illegal drugs a person has taken by measuring how much is in their blood, urine, or other bodily fluid.

Alternative Names

Barbiturates - screen; Benzodiazepines - screen; Amphetamines - screen; Analgesics - screen; Antidepressants - screen; Narcotics - screen; Phenothiazines - screen; Drug abuse screen; Blood alcohol test

How the Test is Performed

Toxicology screening is most often done using a blood or urine sample. However, it may be done soon after the person swallowed the medicine, using stomach contents taken through gastric lavage (stomach pumping) or after vomiting.

How to Prepare for the Test

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

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

How the Test will Feel

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.

Why the Test is Performed

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, monitor drug dependency, and determine the presence of substances in the body for medical or legal purposes.

Additional reasons the test may be performed include:

If the test is used as a drug screen, it must be done within a certain amount of time after the drug was 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): up to 6 to 11 weeks with heavy use

Normal Results

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

A negative value most often means that alcohol, prescription medicines 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 often reported as positive (substance is found) or negative (no substance is found).

What Abnormal Results Mean

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.

Some legal prescription and over-the-counter medicines may interact with the testing chemicals and false results in urine tests. Your provider will be aware of this possibility.

Risks

Risks associated with having blood drawn are slight but may include:

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

Considerations

Substances that may be detected on a toxicology screen include:

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

References

Bluth MH, Pincus MR, Abraham NZ. Toxicology and therapeutic drug monitoring. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 24.

Langman LJ, Bechtel LK, Holstege CP. Clinical toxicology. In: Rifai N, Chiu RWK, Young I, Burnham Carey-Ann D, Wittwer CT, eds . Tietz Textbook of Laboratory Medicine. 7th ed. St Louis, MO: Elsevier; 2023:chap 43.

Minns AB, Clark RF. Substance abuse. In: Walls RM, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 187.

Mofenson HC, Caraccio TR, McGuigan M, Greensher J. Medical toxicology. In: Kellerman RD, Rakel DP, Heidelbaugh JJ, Lee EM, eds. Conn's Current Therapy 2023. Philadelphia, PA: Elsevier; 2023:1404-1457.

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Review Date: 1/2/2023
Reviewed By: Jesse Borke, MD, CPE, FAAEM, FACEP, Attending Physician at Kaiser Permanente, Orange County, CA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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