In general, urine tests are better than blood tests at finding drugs. Traces of a drug may remain in urine longer than in blood. Urine tests often can detect drug use within the last 5 days.
Saliva tests can detect drugs just as well as urine and blood tests do, and they are less invasive than blood tests. (This means they don't require a needle stick.) A saliva test can detect drugs used within the past day.
Trying to change test results by drinking large amounts of water or taking other substances can be dangerous. And it usually doesn't change the results.
A test result that shows drug use or abuse can have serious outcomes, such as arrest or job loss. But the test result may not be accurate. So a positive result should always be confirmed by at least two different test methods.
A standard tox screen can't detect inhalant abuse, when someone sniffs common household products to "get high." Such products include glues, nail polish remover, lighter fluid, spray paints, and cleaning fluids.
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: http://www.usantidoping.org/files/active/athletes/athlete-handbook.pdf.
World Anti-Doping Agency (210). Guidelines for Urine Sample Collection. Available online: http://www.wada-ama.org/Documents/Resources/Guidelines/WADA_Guidelines_Urine_Sample_Collection_v5.1_EN.pdf.
ByHealthwise Staff Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine Specialist Medical ReviewerR. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical Toxicology