Toxicology screen (patient information)

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Toxicology screen


How is the test performed?

How to prepare for the test?

How will the test feel?

Why is the test performed?

What are normal results?

What do abnormal results mean?

What are the risks?


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Toxicology screening

Editor-in-Chief: C. Michael Gibson, M.S.,M.D. [1] Phone:617-632-7753; Associate Editor-In-Chief: Lakshmi Gopalakrishnan, M.B.B.S.


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

How is a toxicology screen performed?

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.

How to prepare for a toxicology screen?

  • 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.

How will a toxicology screen 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 is a toxicology screen 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, 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:
  • 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:

What are normal results?

  • 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).

What do 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.

What are the risks?

  • 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)


Substances that may be detected on a toxicology screen include:


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