Toxicology Tests: What To Think About

Content provided by Healthwise

What To Think About

• Generally, laboratory methods are better able to detect drugs in urine than in blood. The reliability of toxicology tests depends on the methods used by the laboratory. Occasionally drugs that have been taken are not detected (called a false-negative result) or drugs that have not been taken are detected (called a false-positive result).
• Results that indicate drug use or abuse should always be confirmed by at least two different test methods because of the possibility of false results, the possible consequences (such as arrest or loss of a job), and the legal aspects of drug tests.
• Attempts to block or interfere with test results by drinking large amounts of water or taking other substances may be dangerous and usually do not change the test results.
• For suspected drug abuse, a trained person may need to watch the urine or blood collection, and every person who handles the sample must sign a "chain of custody" document that is kept together with the test report. This prevents the substitution or loss of the urine or blood sample.
• A breath test may be used to estimate blood alcohol level. For more information, see the medical test Self-Test for Breath Alcohol.

Last updated:	May 09, 2008
Author:	Jeannette Curtis
Reviewed By:	Kathleen Romito, MD - Family Medicine, R. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care, Medical Toxicology
Editors:	Susan Van Houten, RN, BSN, MBA, Tracy Landauer