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Toxicology Tests

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High levels of prescription or nonprescription medicines may be caused by a drug overdose, either accidental or intentional. A drug overdose may be caused by one large dose of medicine or long-term overuse of a medicine. Interactions between medicines also can cause problems, especially if you start taking a new medicine. A high level may mean that a person is not taking his or her medicine correctly or that the medicine is not being properly processed by the body.

Low values

Low levels of prescription or nonprescription medicines may mean that a person is not taking his or her medicine correctly.

What Affects the Test

Reasons the results may not be helpful include:

  • Some drugs that may be mistaken for others. For example, some cough medicines that do not contain narcotics may be identified as a narcotic.
  • Drinking or eating some types of food (such as a food containing poppy seeds).
  • Having blood in the urine.
  • The amount of time between taking the drug and collecting the sample.
  • Not having a large enough urine sample.

Many medicines may change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.

What To Think About

  • In general, laboratory methods are better able to detect drugs in urine than in blood. Compared to urine and blood tests, saliva tests can provide a less invasive and equally accurate way to detect drugs.
  • 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 mean 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, blood, or saliva 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, saliva, or blood sample.
  • A breath test may be used to estimate blood alcohol level. To learn more, see the topic Self-Test for Breath Alcohol.
  • Standard tests can't detect inhalant abuse. Inhalant abuse is when someone inhales or sniffs common household products to "get high." Such products include—but are not limited to—glues, nail polish remover, lighter fluid, spray paints, and cleaning fluids.

WebMD Medical Reference from Healthwise

Last Updated: March 12, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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