To detect, quantify, and occasionally monitor drugs that are causing acute overdose symptoms; results from emergency and overdose testing are used primarily for treatment purposes; if results are needed for legal proceedings, then specific legal (forensic) procedures must be followed for sample collection, storage, and testing.
Emergency and Overdose Drug Testing
When a person has symptoms such as delirium, difficulty breathing, nausea, agitation, seizures, changes in heart rhythm, characteristic odors, or increased temperature that an emergency room health practitioner thinks may be drug-related; at intervals to monitor a drug overdose
A blood sample drawn from a vein in your arm, a urine sample, or sometimes a breath sample; rarely, saliva or another body fluid
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.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
Emergency and overdose testing may be used to screen for, measure the quantity of, and/or confirm the presence of a drug or toxic substance in someone who is:
- Suspected of overdosing
- Thought to be poisoned
- Showing symptoms of toxicity
Drug testing may be used to help decide how to treat someone who is acutely ill. Once a diagnosis is made, testing may sometimes be used to monitor the effectiveness of treatment and/or monitor the level of the drug or substance in the blood or body.
Results from emergency and overdose testing are primarily used for purposes of treatment. Sometimes test results are used, however, in legal cases for establishing a cause of death or determining if impairment from drugs was a contributing factor in an accident, among other purposes. In these cases, clinical laboratories follow special legal (forensic) procedures for collecting samples, handling them, testing, and reporting of results.
A variety of different approaches may be used to evaluate someone who is suspected to have overdosed or ingested something toxic. Exactly which tests are performed will depend upon the situation and the standard practices of the emergency room (ER). Healthcare practitioners order tests according to their clinical utility, meaning choices are made based on what will be useful, available rapidly, and will help guide treatment. Decisions about tests may be influenced by the turn-around-time for results, tests' sensitivity and specificity, their ability to provide quantitative results, the availability of specific treatments, and the potential for managing the patient's symptoms effectively in the ER.
One approach to making decisions about emergency toxicology testing uses two tiers of testing. The first tier is a group of stat toxicology assays that ideally provides results within an hour and includes tests such as:
- Acetaminophen—often ordered because overdoses are relatively common and can be missed. The affected person may initially have no, few, or nonspecific symptoms, even while significant liver damage is occurring. There is a therapy available for acetaminophen overdose, but it must be given within a few hours of ingestion.
- Salicylates—may be ordered if a person has symptoms consistent with an overdose, an acid base imbalance, or is known to have ingested a significant quantity.
- Ethyl alcohol (ethanol)—a breath test is usually performed in the field and occasionally at the point of care, such as an emergency room. An ethanol blood test is usually sent to a laboratory.
- Methyl alcohol (methanol)—tests are not readily available in most laboratories. When methanol poisoning is suspected, a serum osmolality test is ordered and the osmolar gap is calculated. The osmolar gap is the increase in the number of particles in the blood beyond what is considered normal and will be increased when ethanol, methanol, or ethylene glycol are present in the blood.
- Ethylene glycol (antifreeze)—also requires calculating the osmolar gap, which is also increased when ethylene glycol has been ingested.
- Iron tests—generally used only when iron overdose is suspected in a child or infant.
Not every test is ordered for every patient; the ER health practitioner's choice would be guided by the person's clinical findings.
Also included with first tier testing are several prescribed and monitored medications that can cause toxicity at levels only slightly higher than those needed to treat disease. They include:
- Carbamazepine, often prescribed for seizures and nerve pain
- Digoxin, a heart medication
- Lithium, a psychiatric drug
- Phenobarbital, prescribed for seizure control or anxiety relief
- Phenytoin, used to treat and prevent seizures
- Theophylline, used to prevent and treat wheezing, shortness of breath, and chest tightness caused by asthma, chronic bronchitis, emphysema, and other lung diseases
- Valproic acid, prescribed for seizures, bipolar disorder, and to prevent migraine headaches
Typically one of these tests would only be ordered if a person was regularly taking the drug or if someone was suspected of ingesting it.
A specific hospital might have additional tier one tests on its list, based upon the needs of its community and ER.
The tier two tests include assays for several classes of drugs of abuse, such as cocaine, opiates, amphetamines, barbiturates, and tricyclic antidepressants. The sensitivity and specificity of these tests have improved considerably, but results are still generally interpreted in conjunction with clinical findings.
Confirmatory testing is available but not generally ordered as it is not rapid enough to be useful for treatment decisions.
Other tests that may be ordered to evaluate the person's health status and distinguish between a drug overdose and another cause for the person's symptoms include:
When is it ordered?
Testing may be ordered when a person presents to the emergency room with acute overdose symptoms. Symptoms will vary depending upon what the person has taken, whether multiple drugs were involved, when the substances were ingested and how much, and may vary over time. Two people taking the same types and quantities of drug(s) may exhibit different symptoms. Signs and symptoms may include:
- Changes in consciousness and behavior, ranging from confusion to agitation, paranoia, panic, hallucinations, delirium, lethargy, seizures, unconsciousness, and coma
- Changes in body temperature: hyper- or hypothermia, with pale or reddened skin, dry or sweaty
- Changes in breathing, signs of acid-base imbalance, difficulty breathing, and respiratory failure
- Changes in heart rate and rhythm and in blood pressure, with hypertension or hypotension
- Nausea and vomiting
- Slurred speech and blurred vision
- Characteristic odors
When a person is known to have ingested a specific substance, that drug test will usually be ordered. If testing reveals an overdose of a therapeutic drug but the time of ingestion is unknown, then the test may be repeated several hours later to determine whether concentrations are still increasing.
Serum osmolality and the osmolar gap may be ordered when methanol or ethylene glycol ingestion is suspected.
Supporting tests, such as electrolytes, BUN, creatinine, and liver tests, may be ordered initially and at intervals to evaluate imbalances and organ function and to verify that levels have returned to normal.
What does the test result mean?
Results of tests must be carefully interpreted in conjunction with signs and symptoms. There are established therapeutic and potentially toxic levels for many drugs, but people may experience serious side effects or have symptoms of a drug overdose even when concentrations of drugs are at normal or therapeutic levels.
Symptoms may also be affected by other drugs that are present and by the person's age and state of health. In addition, a positive result for a particular substance does not necessarily mean that the symptoms are due to the substance detected.
Drug concentrations may correlate poorly with a person's overdose symptoms. In general, however, most people will not have symptoms when a drug is at therapeutic concentrations and many will have overdose symptoms as they approach toxic concentrations.
It should be noted that established levels and the units that are used to report them will differ slightly from source to source. It is important to evaluate concentrations in accordance with the testing laboratory's reference ranges. Examples of therapeutic and toxic levels for some drugs in adults include:
Drug Result Possible Interpretation Acetaminophen 10-20 mcg/mL Therapeutic level Less than 150 mcg/mL 4 hours after ingestion Low risk of liver damage Greater than 200 mcg/mL 4 hours after ingestion or greater than 50 mcg/mL 12 hours after ingestion Toxic level; associated with liver damage Aspirin (Salicylic acid, salicylate) 10-100 mcg/mL Therapeutic level for pain relief 100-300 mcg/mL Anti-inflammatory level; may affect stomach and ability to clot; as level increases may cause headache, deafness, vertigo, and tinnitus 250-400 mcg/mL Possibly toxic; may cause vomiting and hyperventilation Greater than 500 mcg/mL Considered toxic Ethanol Greater than 80 mg/dL (>0.08%) Legally intoxicated in most states in individuals older than age 21 years; any level in individuals younger than age 21 years is considered toxic 50-250 mg/dL (0.05%-0.25%) Increasing impairment and depression of central nervous system Greater than 250 mg/dL
Is there anything else I should know?
Sometimes, results from emergency or overdose tests may be used for legal (forensic) purposes in addition to being used to help treat a critically ill person. If such results are to be used in a court of law, then usually sample collection, handling, and testing processes as well as reporting of results are required to follow legal procedures. These may involve some of the following:
- Any samples collected, including blood and urine, are collected into containers that are sealed with a tamper-proof seal.
- Anyone who handles the samples as they are collected, transported, and tested must record their involvement in a document called a "chain-of-custody."
- Preliminary positive results may be reported quickly to facilitate treatment in emergency situations, but then may be later confirmed by a second testing method for legal cases.
Sometimes, medical conditions such as uncontrolled diabetes may produce some of the same symptoms as a drug overdose.
Most of the treatments and antidotes used for drug overdoses must be given within a few hours of the person ingesting the drug. Treatments may work either by preventing the formation of toxic metabolites, such as with acetaminophen, methanol, and ethylene glycol, or by binding to the drug, such as the treatment for a digoxin overdose.
People with drug overdoses must be monitored closely. Changes in consciousness and the ability to breathe unassisted can happen abruptly.
Other procedures may help evaluate a person with suspected overdose or poisoning symptoms. These may include an electrocardiogram (ECG, EKG) to evaluate the heart's rate and rhythm or imaging tests such as magnetic resonance imaging (MRI) or computed tomography (CT) scan.
Why would an ER doctor want to know about all other medications and supplements that a person has taken when it is known that the person has taken a large quantity of a specific drug?
It is important for the health practitioner to consider what drug interactions might be contributing to a person's symptoms.
How would an ER physician evaluate an unconscious person or a child who is unable to tell what he or she has taken?
The health practitioner would select tests based upon the person's clinical findings. The healthcare provider would consider an overdose but also other medical conditions. If the results of initial testing (such as tier one tests) do not show the cause of the person's symptoms and that person's status is unchanged, then additional tests may be ordered to further investigate the cause.
Why might an ER doctor test a person for acetaminophen if he or she denies taking it?
The person might not realize that one or more of the medications that he or she is taking has acetaminophen in it and the person may not initially have symptoms. However, it is important to detect the presence of an overdose of acetaminophen so that the proper treatment can be given as soon as possible after ingestion.
On This Site
Elsewhere On The Web
American Association of Poison Control Centers: Prevention
National Capital Poison Center: Common and Dangerous Poisons
MedlinePlus Health Topics: Poisoning
MedlinePlus Medical Encyclopedia: Drug abuse first aid
MedlinePlus Medical Encyclopedia: Acetaminophen overdose
Centers for Disease Control and Prevention: Prescription Drug Overdoses