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Toxicology Screen

Toxicology Screen

Alternate Names

  • tox screen


A toxicology screen checks a person's blood or urine, or both, for the presence of drugs or other toxic substances. The screen can determine the type and amount of certain drugs or other toxic substances a person may have swallowed, injected, or inhaled. The substances, drugs, or medications detected in the bodily fluids can be legal or illegal.

Who is a candidate for the test?

A healthcare professional may order this test to evaluate for drug overdose, acute or chronic drug poisoning, or drug abuse. An employer may order the test when drug use may pose a threat to work performance or might endanger others, or for other legal proceedings.

How is the test performed?

To perform a blood test for a toxicology screen, a blood sample is taken from a vein in the arm. First, the skin over the vein is cleansed with an antiseptic. A rubber tube is wrapped around the upper arm and tightened to enlarge the veins. A small needle is gently inserted into a vein, and blood is collected for testing in the laboratory. After the wrap is removed, a cotton ball will be held over the needle site for a short time until bleeding stops.
A urine toxicology screen is usually used to test for the use or abuse of drugs that are nonprescription or illegal. To test for drugs in urine, a urine sample is usually taken by having the person urinate into a container in the presence of a healthcare professional.
The sample is checked on site for possible errors in handling and then sent to a laboratory for testing. The healthcare professional may ask for any variety of physical, microscopic, and chemical tests. It is best to do most tests within 15 minutes of the time the urine was collected.

What is involved in preparation for the test?

The person should request specific instructions from his or her healthcare professional.

What do the test results mean?

Normal values for toxicology screens depend on the institution performing the tests. In general, the following values apply:
  • There should be no illegal drugs in the blood or urine.
  • There are acceptable levels for over-the-counter medications. These are called therapeutic levels.
  • There should be no alcohol.
  • Cigarette smoking may affect some test results.
  • The presence of nonprescription drugs may show unapproved drug use.
  • Specific tests can show the drug used.
  • High alcohol levels may show intoxication.
Commonly abused drugs that may be detected in the urine include:
  • marijuana (pot)
  • cocaine
  • phencyclidine (PCP)
  • amphetamines
  • morphine, heroin, or codeine
  • barbiturates


Tabers Cyclopedic Medical Dictionary, F.A.Davis, 1993

Illustrated Guide to Diagnostic Tests, Springhouse, 1998

Mosby's Manual of Diagnostic and laboratory Tests, Kathleen Pagana and Timothy Pagana, 1998

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