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 drugs or other toxic substances a person may have swallowed, injected, or inhaled. The substances, drugs, or medications detected in the bodily fluids or "screened for" can be legal or illegal.

Who is a candidate for the test?

A healthcare provider may order this test to evaluate for drug overdose, poisoning, or drug abuse. An employer may order the test when drug use may pose a threat to work performance or might endanger others. This test is used to find the causes of acute drug poisoning. The tests can be used for legal proceedings too.

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 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 midstream (or "clean-catch") urine sample is taken usually in the presence of a healthcare provider.

First, the person washes around the urethra, the tube that passes urine out of the body. This prevents contamination of the sample. Next, the person urinates and collects a urine sample in midstream, that is, not at the beginning and not at the end of urination. This is referred to as a clean-catch urine sample.

The person should follow these steps to get the sample. First, the person starts urinating into the toilet. Then, he or she catches a sample of urine in a container. Then the person may finish urinating in the toilet. The person then covers the container and gives it to the healthcare provider.

The sample is sent to a laboratory for testing. The healthcare provider may ask for any variety of physical, microscopic, and chemical tests. It is best to do most tests within 15 minutes from the time the urine was collected.