Toxicology Tests

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Test Overview

A toxicology test ("tox screen") checks for drugs or other chemicals in your blood, urine, or saliva. Drugs can be swallowed, inhaled, injected, or absorbed through the skin or a mucous membrane. In rare cases, a tox screen may check your stomach contents or sweat.

A tox screen may check for one certain drug or for up to 30 different drugs at once. These may include prescription medicines, nonprescription medicines (such as aspirin), vitamins, supplements, alcohol, and illegal drugs, such as cocaine and heroin.

Testing is often done on urine or saliva instead of blood. Many drugs will show up in a urine or saliva sample. And urine and saliva tests are usually easier to do than blood tests.

Why It Is Done

This test may be done to:

  • Find out if a drug overdose may be causing life-threatening symptoms, unconsciousness, or strange behavior. It is usually done within 4 days after a drug may have been taken.
  • Check for drug use in the workplace. Testing is common for people who work in public safety, such as bus drivers or child care workers. Some jobs require a tox screen as part of the hiring process.
  • Check for drug use in students involved in extracurricular activities, such as sports and cheerleading.
  • Look for the use of drugs that enhance athletic ability.
  • Check for the presence of a date rape drug.

How To Prepare

Many medicines can change the results of this test. So give your doctor a list of all the medicines you have taken in the past 4 days. Be sure to include any prescription and over-the-counter medicines, vitamins, and natural health products.

You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done. If you are a student, your parents may also need to sign a consent form before you can be tested.

Talk to your doctor if you have any concerns about 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

Collecting the urine this way keeps the sample from being contaminated.

  • Wash your hands to make sure they are clean before you collect the urine.
  • If the collection cup has a lid, remove it carefully. Set it down with the inner surface up. Do not touch the inside of the cup with your fingers.
  • Clean the area around your genitals.
    • For men: Pull back the foreskin, if you have one. Clean the head of the penis thoroughly with medicated towelettes or swabs.
    • For women: Spread open the folds of skin around the vagina with one hand. Then use your other hand to clean the area around the vagina and urethra thoroughly with medicated towelettes or swabs. Wipe the area from front to back to avoid spreading bacteria from the anus to the urethra.
  • Start urinating into the toilet or urinal. Women should keep holding apart the folds of skin around the vagina while they urinate.
  • After the urine has flowed for several seconds, place the collection cup into the stream. Collect about 3 fl oz (90 mL) of this "midstream" urine without stopping the flow.
  • Do not touch the rim of the cup to your genital area. And don't get 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 cup. Return the cup to the lab. If you are collecting the urine at home and can't get it to the lab in an hour, refrigerate it.

If you are being tested for drug abuse, a trained person of the same sex will watch you give the sample. This is to make sure that you are providing your own 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 fresh.

Saliva test

The person who collects the sample will either:

  • Swab the inside of your cheek, or
  • Ask you to spit into a tube.

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

It is not painful to collect a urine sample. Another person may watch while you collect the sample. This may make you feel uncomfortable.

Saliva test

It is not painful to collect a saliva sample. Another person will collect the sample or watch you collect the sample.


Blood test

There is very little chance of a problem from having a 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. You can treat this by using a warm compress several times a day.

Bleeding can be a problem for people who have bleeding disorders or take blood-thinning medicines such as aspirin or warfarin (Coumadin). 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

Collecting a urine sample does not cause problems.

Saliva test

Collecting a saliva sample does not cause problems.


A toxicology test (tox screen) checks for drugs or other chemicals in your blood, urine, or saliva.

Most tox screens are qualitative tests. This means they only find out if drugs are present in the body, not the exact level or quantity. Follow-up quantitative testing is often done to find the level of a drug in the body and to confirm the results of the first test.

Toxicology tests

No unexpected drugs are found in the sample.

Levels of prescription or nonprescription medicines found in the sample are within the effective (therapeutic) range.


Unexpected drugs are found in the sample.

Levels of prescription or nonprescription medicines found in the sample are:

  • Below the effective (therapeutic) range, or
  • Above the therapeutic range, or
  • High enough that they may be toxic.

High values

High levels may be caused by a drug overdose, either by accident or on purpose. 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 when you start to take a new medicine. A high level may mean that you are not taking your medicine correctly or that your body is not processing the medicine as it should.

Low values

Low levels of prescription or over-the-counter medicines may mean that you are not taking your medicine correctly.

What Affects the Test

You may not be able to have the test, or the results may not be helpful, if:

  • You drink or eat some types of food (such as a food that contains poppy seeds).
  • You have blood in your urine.
  • There is too much time between taking the drug and collecting the sample.
  • You don't give a large enough urine sample.

Many medicines may change the results of this test. And the test may mistake some drugs for others. For example, some cough medicines that do not contain an opiate may be identified as a narcotic.

What To Think About

  • 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.
  • Tox screen results are not always accurate. Sometimes a test may not find drugs that have been taken (false-negative result). Or a test may find drugs when they have not been taken (false-positive result).
  • 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.
  • A breath test may be used to estimate blood alcohol level. To learn more, see the topic Self-Test for Breath Alcohol.


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 online:


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

Current as ofAugust 21, 2015