Some drugs that may be mistaken for others. For
example, some cough medicines that do not contain
narcotics may be identified as a
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
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
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
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
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.
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.
Other Works Consulted
Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
U.S. Anti-Doping Agency (2011). Athlete Handbook. Available online:
World Anti-Doping Agency (210). Guidelines for Urine Sample Collection. Available