Emergency and Overdose Drug Testing
At a Glance
Why Get Tested?
To detect, measure, and occasionally monitor drugs that are causing acute overdose symptoms; results from emergency and overdose testing are used mainly for to help treatment. If results are needed for legal proceedings, then special legal (forensic) procedures must be followed for sample collection, storage, and testing.
When to Get Tested?
When a person has symptoms such confusion, difficulty breathing, feeling sick, agitation, fits, changes in heart rhythm, or increased temperature that the Accident and Emergency (A&E) doctor thinks may be drug-related; at intervals to monitor a drug overdose
Sample Required?
A blood sample taken from a vein in your arm, a urine sample, or sometimes a breath sample; rarely, saliva or another body fluid
Test Preparation Needed?
None
The Test Sample
What is being tested?
Emergency and overdose drug testing is requested for single drugs or groups of drugs by an A&E or Intensive Care doctor to detect, assess, and monitor someone who has a drug overdose. A drug overdose may be caused by a variety of prescription and over-the-counter (OTC) medicines, illegal drugs, and household substances. Once inside the body, these substances are often broken down by the liver and removed in the urine.
Some substances only cause symptoms if they are present at high levels or are above the preferredlevels used for treatment. Some common examples of these include:
Some substances can cause symptoms at both low and high levels 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 breakdown products (metabolites). Examples of these toxins include:
Eating or drinking a variety of other drugs and chemicals may cause rapid toxicity. This article only describes a small number of drugs and other substances which are more commonly tested for in the clinical laboratory. Some of the groups 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:
A good example of a drug which has a toxic breakdown product is paracetamol, a common pain reliever that is also present in a variety of other prescription medicines. One of the breakdown product of paracetamol is toxic to the liver, but the liver can detoxify the small amounts formed after normal doses of paracetamol. However, if someone takes more paracetamol than the liver can process, then the toxic product builds up, damaging the liver and, in some cases, causing liver failure.
Illegal Drugs
Overdoses of illegal drugs can also occur. The particular illicit drugs seen in the A&E department will depend on their used in the local community and on their ability to cause acute symptoms alone or in combination with other substances. Certain drugs, such as cannabis/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 loss of consciousness but are removed so rapidly that testing for them is rarely useful. For more information on these, see the article on Drugs of Abuse Testing.
Household Substances
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, and metals such as lead and mercury can also have toxic effects. For more information, contact NHS direct (NHS 24 in Scotland).
How is the sample collected for testing?
A blood sample is collected by inserting a needle into a vein in the arm. Urine and saliva need to be collected in clean containers. A breath sample may be used and 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.
The Test
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:
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 follow the effectiveness of treatment and/or the level of the drug or substance in the blood or body.
Results from emergency and overdose testing are mainly used for treatment. If results are needed for legal cases, for example, finding the cause of death or if drugs had contributed to the cause of an accident, then special legal (forensic) procedures for the collection, handling, testing of samples, and reporting of results must be followed. A variety of different approaches may be used to investigate someone who is thought to have taken an overdose or eaten or drunk something toxic. What is requested is will depend on what will be useful to the A&E doctor, be available rapidly, and will help guide treatment. In many cases, treatment is directed to particular clinical problems, and the particular toxin does not influence the treatment. Selection of tests may be influenced by how quickly they can be done, test sensitivity and specificity, the ability to provide quantitative results, the availability of treatment, and the potential for treating the patient's symptoms in the A&E department.
One approach, recommended by the UK National Poisons Information Service (NPIS) and the Association for Clinical Biochemistry (ACB) uses two tiers of testing. The first tier is a group of toxicology tests that should be available , 24 hours a day, in all hospitals that have patients with acute poisoning. These tests are:
The A&E doctor's choice of tests will be guided by the person's symptoms. Other first tier tests are some drugs that can cause toxicity at levels only slightly higher than those needed to treat disease. They include:
Typically these tests would only be requested if a person was regularly taking the drug.
The second tier of toxicology tests includes a range of specialist or infrequently required tests, which are normally not required with the same degree of urgency and may be referred to regional specialist toxicology centres. Such tests include methanol and ethylene glycol (see below), poisonous metals such as arsenic, lead, and mercury, acetylcholinesterase, paraquat, phenobarbital, and therapeutic drugs like methotrexate and thyroxine.
Second tier testing also includes testing for several groups of drugs, such as cocaine, opiates, amphetamines, barbiturates, and tricyclic antidepressants. These tests are not for particular drugs but for whole groups and must be interpreted carefully in conjunction with clinical findings. In rare and very severe cases of poisoning, a broad screen of a range drugs may be requested, but this is a complex and time-consuming procedure which rarely contributes to helping treatment.
Other tests may be requested with the drug test to help make a diagnosis and distinguish between a drug overdose and other causes of the person's symptoms. These tests may include:
When is it requested?
One or more emergency drug overdose tests may be requested when a person appears in the A&E department with symptoms of acute overdose. Symptoms will vary depending upon what the person has taken, whether lots of drugs are involved, when and how much of the substances were taken, and over what period time. Two people taking the same types and quantities of drug(s) may have different symptoms. Signs and symptoms may include:
When a person is known to have taken a particular substance, then a test for that drug test may be requested to help with treatment. For an overdose of a therapeutic drug and the time it was taken is unknown, then the test may be repeated several hours later to see whether its concentration is still increasing. In most cases, drug concentrations are not measured to check whether treatment is working.
Serum osmolality and the osmolar gap (see above) may be used whenever methanol or ethylene glycol ingestion is suspected.
Supporting tests, such as electrolytes, urea, creatinine, and liver test may be used initially and at intervals to check that levels have returned to normal.
What does the test result mean?
Results of tests must be interpreted carefully 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 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. The levels and the units used to report drug test will be differ slightly from laboratory to laboratory. Drug levels must be interpreted using testing laboratory's reference ranges. Examples of levels for some drugs in adults include:
| Drug | Normal/Therapeutic | Toxic Level | Comments |
| Aspirin (Salicylic acid, salicylate) | < 100 mg/L | Pain relief | |
| 150-300 mg/L | > 100 mg/L | Anti-inflammatory dose, may affect stomach and blood clotting, as level increases may cause headache, deafness, vertigo, and tinnitus | |
| 250-400 mg/L | Vomiting and hyperventilation | ||
| > 500 mg/L | Toxic | ||
| Ethanol | > 80 m/dL |
Legal definition of unfitness to drive |
|
| 80-400 mg/dL |
Increasing impairment and depression of central nervous system | ||
| >400 mg/dL | Potentially fatal | ||
| Paracetamol | 10-20 mg/L |
>200mg/L | Toxic level at 4 hours after ingestion in most patients (a level of 100mg/L is used to define toxicity in patients who are alcoholic, malnourished or taking certain prescribed drugs) |
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 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:
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 paracetamol, 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 assess a person with suspected overdose or poisoning symptoms. These may include an electrocardiogram (ECG) to evaluate the heart's rate and rhythm or imaging tests such as resonance imaging (MRI) or computed tomography (CT)
Common Questions
Ask a Laboratory Scientist
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
