Emergency and Overdose Drug Testing
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 metabolites. Examples of these toxins include:
- 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 OTC example of a 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 the prevalence in the community and on their ability to cause acute symptoms alone or in combination with other substances. Some drugs of abuse are "diverted" prescription medications such as oxycodone or amphetamine. Drugs, such as cannabinoids/marijuana, 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 seen include methanol, isopropyl alcohol, and ethylene glycol (antifreeze), which may be used by some people as substitutes for ethanol. Other poisons, such as rodenticides, aerosol and cleaning products, insecticides, heavy metals, etc. can also have toxic effects. (For more information, see the website 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. If results are needed for legal cases, for example, establishing a cause of death or determining if impairment from drugs was a contributing factor in an accident, then special legal (forensic) procedures in the collection, handling, testing of samples, and reporting of results must be followed. One example is if a blood sample is to be used for ethanol testing in a legal case, then the arm should be cleaned with something other than alcohol before the sample is collected.
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). What is ordered is governed by clinical utility - what will be useful to the ER doctor, available rapidly, and will help guide treatment. Choices may be influenced by the turn-around-time for test results, test sensitivity and specificity, the 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, recommended by the National Academy of Clinical Biochemistry (NACB), utilizes 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 - a level is 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 - this test 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 at the point of care such as an emergency room; a blood test is usually sent to a laboratory.
- Methyl alcohol (Methanol) - a test for methanol is not readily available in most laboratories, so if methanol poisoning is suspected, a serum osmolality test is done and the osmolar gap calculated. The osmolar gap is an increase in the number of particles in the blood beyond what is considered normal. The osmolar gap will be increased when ethanol, methanol, or ethylene glycol are present in the blood.
- Ethylene glycol (antifreeze) - the osmolar gap is also increased when ethylene glycol has been ingested.
- Iron tests - usually only used when iron overdose is suspected in a child or infant.
Not every test is ordered on every person; the ER doctor's choice would be guided by the person's clinical findings.
Also included with NACB 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:
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.
Tier two testing includes testing for several classes of drugs of abuse, such as cocaine, opiates, amphetamines, barbiturates, and tricyclic antidepressants. These tests have less than ideal sensitivity and specificity and must be 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 along with emergency drug overdose testing in order 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?One or more emergency drug overdose tests may be ordered when a person presents to the ER 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
When a person is known to have ingested a specific substance, then that drug test will usually be ordered. If an overdose of a therapeutic drug is detected, but the time of ingestion is unknown, then the test may be repeated several hours later to determine whether concentrations are still increasing. In most cases, drug concentrations are not monitored to verify the effectiveness of treatment.
Serum osmolality and the osmolar gap may be ordered whenever a 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 levels for some drugs in adults include:
Drug Normal/Therapeutic Toxic Level Comments Acetaminophen 10-20 mcg/mL > 150 mcg/mL Toxic level at 4 hours after ingestion Aspirin (Salicylic acid, salicylate) < 100 mcg/ML Pain relief 150-300 mcg/mL > 100 mcg/mL Anti-inflammatory dose, may affect stomach and ability to clot, as level increases may cause headache, deafness, vertigo, and tinnitus 250-400 mcg/mL Vomiting and hyperventilation > 500 mcg/mL Intoxication Ethanol > 80 mg/dL (>0.08%) Legally intoxicated in most states 80-400 mg/dL (0.08%-0.40%) Increasing impairment and depression of central nervous system > 400 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.
Other medical conditions, such as uncontrolled diabetes, may produce some of the same symptoms as a drug overdose.
Most of the treatments and antidotes that are used must be given within a few hours of the person ingesting the drug. They may work by either 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.
Patients 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 they have taken a large quantity of a specific drug?
How would an ER doctor evaluate an unconscious person or a child who is unable to tell them what has been taken?The doctor would base their selection of tests based upon the person’s clinical findings. They would consider an overdose but also consider 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 their status is unchanged, then the doctor may order additional tests to further investigate the cause.
Why might an ER doctor test a person for acetaminophen if they say that they have not taken it?The person might not realize that one or more of the medications that they are taking have acetaminophen in them 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.