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The Test Sample
What is being tested?
A variety of prescription and over-the-counter (OTC) medications, illegal drugs, and household substances can cause drug overdoses. Emergency and overdose drug testing is ordered for single drugs or groups of drugs by an emergency room (ER) health practitioner to detect, evaluate, and monitor a drug overdose.
Drugs and related substances that are ingested or absorbed are typically broken down (metabolized) by the liver over a period of time and then eliminated from the body, primarily in the urine. The rate at which this happens depends on a number of factors ranging from age, weight, and sex to food intake and presence of underlying diseases. Moreover, the development of toxicity depends on the type of substance absorbed or ingested.
Some substances cause symptoms only if they are present in high concentrations or above therapeutic levels. Some common examples of these include:
- Acetaminophen—an ingredient in many over-the-counter preparations; it can cause significant liver damage if recommended doses are exceeded.
- Aspirin (also known as salicylates)—at higher levels, it can cause an acid-base imbalance.
- Therapeutic drugs—used to treat conditions such as heart failure and epilepsy
Some substances can cause symptoms at both low and high concentrations depending on the user. Long-term users of drugs such as alcohol and illegal drugs (drugs of abuse) may be able to tolerate more drug than someone who is taking it for the first time.
Other substances are toxic at any concentration and some have toxic break-down products (metabolites). Examples include:
- Toxic alcohols, including methanol and isopropanol
- Ethylene glycol (antifreeze)
Ingestion of a variety of other drugs and chemicals may cause acute toxicity. This article is limited to the drugs and a few other substances more commonly tested for in the clinical laboratory. Some of the various general categories of substances that may be tested are listed below:
Prescription and over-the-counter (OTC) medications
Overdoses caused by prescription and OTC drugs may be due to:
- Ingestion of too much of a medication
- Interaction of multiple drugs
- A decrease in the body's ability to eliminate a drug and/or its metabolite; many drugs are processed by the liver; that is, the liver changes the drug into a different form, which is then eliminated from the body. If the liver or kidneys are not working properly, then the drug and/or its metabolite may build up in the body.
A classic example of an OTC drug with a toxic metabolite is acetaminophen, a common pain reliever that is also a component of a variety of other OTC and prescription medicines. One of the metabolites of acetaminophen is toxic to the liver, but the liver is able to detoxify "normal" amounts of it. However, if someone takes more acetaminophen than the liver can process, then the toxic metabolite builds up, damaging the liver and, in some cases, causing liver failure.
Overdoses of illegal drugs can also occur. The illicit drugs encountered in the ER depend on their prevalence in the community and whether these substances cause acute symptoms alone or in combination with other substances. Some drugs of abuse are "diverted" prescription medications, such as oxycodone or amphetamine. Some drugs, such as marijuana and other cannabinoids, can linger in the body for days to weeks but rarely cause overdose symptoms. Other substances, such as gamma-hydroxybutyrate (GHB), can cause acute symptoms such as a loss of consciousness but are metabolized so rapidly that testing for them is rarely useful. For more on these, see the article on Drugs of Abuse Testing.
There are a wide variety of household substances that may be abused or accidentally ingested. Those commonly involved in emergency drug testing include methanol, isopropyl alcohol, and ethylene glycol (antifreeze), which some people ingest as substitutes for ethanol, also known as grain alcohol. Other poisons, such as rodenticides, aerosol and cleaning products, insecticides, and heavy metals, can also have toxic effects. (For more information, see the web site of the American Association of Poison Control Centers.)
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. Urine and saliva are collected in clean containers. A breath sample is collected by blowing through a tube, into an instrument.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.