Toxicology Tests

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Toxicology Tests

Test Overview

A toxicology test checks blood or urine for the presence of drugs or chemicals. In rare cases, stomach contents, sweat, or saliva may also be checked.

Drugs can be accidentally or deliberately swallowed, inhaled, injected, or absorbed through a skin surface or mucous membrane. These include prescription medicines, non-prescription medicine (such as ASA or acetaminophen), vitamins, nutritional supplements, alcohol, and illegal drugs, such as cocaine and heroin.

A toxicology test may check for one specific drug or for up to 30 different drugs at once. Testing is often done on a urine sample instead of blood, because urine tests are usually easier to do than blood tests and many drugs show up in the urine. Also, traces of a drug may remain in urine for longer than in blood.

Why It Is Done

A toxicology test ("tox screen") can be done to:

  • Help find the cause of life-threatening symptoms, unconsciousness, or bizarre behaviour in an emergency situation. It is usually done within 96 hours (4 days) after a drug may have been taken. The toxicology test is used to find out if symptoms may be caused by a drug overdose. Both a urine sample and a blood sample may be tested.
  • Test for drug use in the workplace, especially for people who are involved with public safety, such as bus drivers or child care workers. A toxicology test may also be a normal part of the application procedure for some jobs. This may be done on either a blood or urine sample.
  • Test athletes for the use of drugs that enhance their athletic ability. This is usually done on a urine sample.
  • Evaluate the possible use of date rape drugs. This is usually done on a urine sample.

How To Prepare

Many medicines may change the results of this test. Be sure to tell your doctor about all the non-prescription and prescription medicines you take. Make a list of any medicines (prescription and non-prescription), herbal supplements, vitamins, and other substances you are taking or have taken in the past 4 days.

You will need to sign a consent form that says you understand the risks of the toxicology testing and agree to have it done. Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?).

How It Is Done

Blood test

The health professional taking a sample of your blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

Clean-catch midstream urine collection

When testing for drug abuse, another person will watch you to make sure that the sample you are providing is your urine and that you have not added anything to the sample. The temperature of the urine may also be tested to make sure that it is a fresh sample.

This collection method prevents contamination of the sample. Wash your hands to make sure they are clean before collecting the urine.

  • If the collection container has a lid, remove it carefully and set it down with the inner surface up. Do not touch the inside of the container with your fingers.
  • Clean the area around your genitals.
    • A man should retract the foreskin, if present, and clean the head of his penis thoroughly with medicated towelettes or swabs.
    • A woman should spread open the folds of skin around her vagina with one hand, then use her other hand to clean the area around her vagina and urethra thoroughly with medicated towelettes or swabs. She should wipe the area from front to back to avoid contaminating the urethra with bacteria from the anus.
  • Begin urinating into the toilet or urinal. A woman should continue holding apart the folds of skin around the vagina while urinating.
  • After the urine has flowed for several seconds, place the collection container into the stream and collect about 90 mL (3 fl oz) of this "midstream" urine without stopping the flow.
  • Do not touch the rim of the container to your genital area, and avoid getting toilet paper, pubic hair, stool (feces), menstrual blood, or other foreign matter in the urine sample.
  • Finish urinating into the toilet or urinal.
  • Carefully replace the lid on the container and return it to the lab. If you are collecting the urine at home and cannot get it to the lab within an hour, refrigerate the sample.

How It Feels

Blood test

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Urine test

There is no pain while collecting a urine sample. A trained person of the same sex may need to watch you during the urine collection. This may make you feel uncomfortable.


Blood test

There is very little chance of a problem from having blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
  • Ongoing bleeding can be a problem for people with bleeding disorders. ASA, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Urine test

There is no chance for problems while collecting a urine sample.


A toxicology test examines blood, saliva, or urine for the presence of drugs. Most toxicology tests determine only the presence of drugs (called qualitative testing) in the body and not the specific level or quantity. Follow-up testing is often required to determine the exact level of a certain drug in the body (called quantitative testing) and to confirm the results of initial testing.

Toxicology tests

No unexpected drugs are found in the blood or urine.

Levels of prescription or non-prescription medicines found in the blood or urine are within the effective (therapeutic) range.


Unexpected drugs are found in the blood or urine.

Levels of prescription or non-prescription medicines found in the blood or urine are too low or too high to be effective (therapeutic) or potentially toxic, if too high.

High values

High levels of prescription or non-prescription 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 non-prescription 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 non-prescription and prescription medicines you take.

What To Think About

  • In general, 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 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 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 topic Self-Test for Breath Alcohol.


Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th 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 (2006). Athlete Handbook. Available online:
  • World Anti-Doping Agency (2004). Guidelines for Urine Sample Collection, Version 4. Available online:


By Healthwise Staff
Primary Medical Reviewer Kathleen Romito, MD - Family Medicine
Primary Medical Reviewer Brian D. O'Brien, MD - Internal Medicine
Specialist Medical Reviewer R. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical Toxicology
Last Revised July 9, 2010

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