To detect salicylate overdose, to help evaluate its severity and monitor its resolution; sometimes to monitor for an overdose if you regularly use prescription-strength salicylates
When you have symptoms such as nausea, hyperventilation, ringing in the ears (tinnitus), irregular heart beat (arrhythmia), or confusion that may be from taking too much aspirin or medications with salicylate ingredients; when it is suspected that an unconscious person or a child may have ingested a significant quantity of a salicylate, often as part of emergency and overdose testing; at regular intervals when monitoring an overdose; sometimes on a regular basis if you take a prescription salicylate for rheumatoid arthritis or other autoimmune disorder
A blood sample drawn from a vein and/or sometimes a urine sample collected in a clean container
None, but your healthcare practitioner may ask when you last took a salicylate and the amount taken. To accurately interpret results, blood samples are usually drawn at least 4 hours after ingestion. If you regularly take a prescription salicylate, your healthcare practitioner may want to collect blood just prior to your next dose (trough level). Tell your healthcare provider about any other prescribed or over-the-counter medications you are taking.
Salicylates are a group of drugs, including aspirin, available as both prescription and non-prescription (over-the-counter) medications. They are often used to relieve pain and inflammation, to reduce fever, and to prevent excessive blood clotting. Salicylate testing measures the concentration in the blood to detect and/or monitor an overdose (salicylate poisoning).
Salicylates are available as pills or tablets taken by mouth or as topical creams absorbed through the skin. Aspirin is the most common salicylate taken as tablets or pills.
- Over-the-counter salicylates are used as needed or regularly to reduce pain, fever, and inflammation.
- Low doses of aspirin may be taken on a regular basis to reduce the chance of inappropriate blood clotting (thrombosis), heart attack, or stroke in people who have a high risk of developing these disorders. Low-dose aspirin may also be used to prevent worsening of cardiovascular disease and/or complications in someone who is having a heart attack or who recently experienced one. However, aspirin for cardiovascular disease prevention is no longer recommended in patients 70 or older, or those with bleeding disorders.
- Aspirin is also used in patients with myeloproliferative neoplasms (e.g., polycythemia vera, essential thrombocythemia) to prevent blood clot formation.
- Uncommonly, prescription-strength aspirin may be used to relieve symptoms of rheumatoid arthritis (RA) and osteoarthritis as well as symptoms of autoimmune disorders such as lupus.
With single, normal doses, blood concentrations of salicylates typically peak in about 2 hours, but this may be delayed for 12 hours or more with "enteric-coated" or "sustained-release" preparations. If too much salicylate is consumed (acute poisoning with a large dose) or too much is taken over time (chronic poisoning), then associated signs and symptoms will develop.
Salicylates are metabolized by the liver and eliminated from the body in the urine. The ability to remove salicylates efficiently is affected by the body's blood and urine pH (acidity/alkalinity) and by kidney and liver function. People with impaired liver or kidney function may be more susceptible to salicylate toxicity.
Salicylate poisoning is a serious condition that often requires hospitalization and careful monitoring. In severe cases, the acid-base imbalance that it causes can worsen over time, causing electrolyte imbalances (hyperkalemia), low blood glucose, and dehydration, and leading to convulsions, hallucinations, delirium, coma and even death.
Both acute and chronic toxicity will present with similar symptoms, but chronic toxicity is associated with lower levels of salicylate. In addition, chronic toxicity is more likely to occur in the elderly, causing delirium, lack of energy, fluid build-up in the lungs (pulmonary edema), kidney failure, acid-base disorders, and/or abnormal electrolytes. Many of these symptoms are already present in elderly patients not taking salicylates, so detecting salicylate overdose/poisoning can be difficult.
When used with care and following dosing directions, therapeutic doses of salicylates are safe and effective for most adults. However, adults can run into trouble with salicylates when they unknowingly combine multiple products that contain them.
- Many over-the-counter medications include a salicylate as one of the ingredients. If you are unaware of the ingredients, you can mistakenly take more than one of these drugs together, resulting in a cumulative effect and a high amount of ingested salicylate.
- Widespread and easy availability of salicylate-containing medications can also mislead some to think that it is very safe and that "more is better."
- An overdose can occur when you have pain that is not relieved with an initial dose and, unaware of the danger, take more than the recommended dose and/or take additional doses too soon.
- In the elderly, these scenarios can especially be a problem because underlying conditions and general health status can decrease the ability to eliminate salicylates from the body.
Aspirin is not recommended for use in children and teens because of the risk of developing Reye syndrome, a disease characterized by acute brain damage, resulting in changes in behavior, nausea, vomiting, and liver dysfunction that can be fatal. Though youth are not routinely given aspirin, they may become poisoned through accidental or intentional ingestion. Topical creams that contain salicylates are of special concern as they contain very high doses.
How is the test used?
This test is used to detect a high level of salicylate in the blood. It may be used to:
- Help diagnose an overdose (salicylate poisoning). It may be ordered along with other tests associated with emergency and overdose drug testing. The specific tests ordered will depend upon the symptoms and clinical signs.
- Monitor levels over time if a toxic concentration is detected with initial testing. A series of salicylate tests may be ordered to determine whether the salicylate level has increased or has peaked and started to drop. This information is used to help monitor your health status and help guide treatment.
- Monitor for an overdose if you take a prescription-strength salicylate, either to determine if the level is within a therapeutic range or to make sure you are not taking too much. This may be especially appropriate if your other medications, or health status, have changed.
When is it ordered?
Salicylate testing may be ordered when it is suspected you have ingested a large amount of aspirin or other drugs containing salicylate. Usually, blood is drawn and tested at least 4 hours after last known ingestion. Results from tests done earlier than this are difficult to interpret.
Testing may be ordered when you have symptoms associated with an acute or chronic salicylate overdose. Typically, these symptoms will appear 3 to 8 hours after initial ingestion in cases of acute toxicity and may include:
- Nausea and vomiting
- Hyperventilation (rapid breathing); less common in children
- Ringing in the ears (tinnitus)
Additional symptoms that may develop include:
- Convulsions, seizures
- Rapid heart rate
- Overheating (hyperthermia), especially in young children with severe toxicity
- Shortness of breath due to fluid accumulation in the lungs (pulmonary edema)
- Bleeding (rare)
Testing may be done when people are suspected of wanting to harm themselves (suicidal tendencies).
When acute salicylate toxicity is detected, a healthcare practitioner may order the test as frequently as every 2 to 3 hours to monitor the resolution of the overdose. Salicylate levels will continue to be monitored until there are two consecutive results that show a decrease from peak levels. Clinical signs of salicylate poisoning/toxicity will also be monitored frequently.
When you take regular doses of a prescribed salicylate, your healthcare practitioner may order this test on a routine basis to check for an elevated level since chronic toxicity may develop without obvious signs and symptoms, or with symptoms that develop slowly and are nonspecific (i.e., may be seen with many other conditions).
What does the test result mean?
Normal therapeutic blood concentrations of aspirin and other salicylates depend upon what the drug is being used for, and blood levels must be interpreted along with your medical history and clinical signs and symptoms. Lower blood levels are sufficient for pain relief and to lower risk of blood clots, but higher levels may be required for managing inflammation in rheumatic conditions such as arthritis. At these higher levels, some side effects may become apparent.
The severity of signs and symptoms, and at what dose they appear, depends upon the individual. Symptoms may be seen with blood levels that are generally considered to be therapeutic in inflammatory conditions, and they will tend to appear in many people at levels of about 10-30 mg/dL. This is especially true in patients who may have kidney or liver disease. In general, the severity of salicylate toxicity increases with increasing concentrations.
The table below summarizes some results that may be seen. These numbers typically represent a blood sample that is collected at least 4 hours after last dose:
Salicylate result reported as mg/dL Salicylate result reported as mcg/mL Result Interpretation 2-10 20-100 Therapeutic level for pain relief (analgesia) 10-30 100-300 Anti-inflammatory level; some symptoms of toxicity may appear, such as headache, tinnitus, vertigo Greater than 30 Greater than 300 Considered toxic
Note: Some laboratories report salicylates as milligrams per deciliter (mg/dL) while others report micrograms per milliliter (mcg/mL). These two are different by a factor of 10.
Rising levels (when you have not taken more salicylate) indicate that peak salicylate concentrations have not yet been reached. In an otherwise healthy person, peak salicylate levels occur 2 hours after ingestion. However, in cases of a large ingestion of pills or tablets, hard, solid masses (concretions or bezoars) can form, delaying the peak by six hours or more. A delay in peak levels can also occur if the person ingested "enteric" or "sustained-release" forms of salicylate.
Falling salicylate levels tend to indicate that the excess is being eliminated by the body and that the overdose is resolving. This is confirmed by two decreasing levels of salicylate once peak concentration has been reached.
What other tests might be ordered in emergency or overdose cases?
In emergency situations, a salicylate test may be ordered with other tests, such as:
- Arterial blood gases and electrolytes to evaluate oxygenation and acid-base balance
- Blood urea nitrogen (BUN) and creatinine to evaluate kidney function
- Urinalysis to monitor urine pH
- Glucose to detect low blood sugar
- Liver panel to evaluate liver function (AST, ALT)
- Coagulation profile to assess blood clotting (PT, PTT, platelet count)
Is there anything else I should know?
Be aware that many prescription and nonprescription medications contain salicylates in combination with other medications. Do not take more than one medication that contains salicylates at a time.
Aspirin should not be taken long-term without consulting a healthcare practitioner and should NEVER be given to children or teens unless directed by a healthcare provider. Aspirin should not be taken with alcoholic drinks as this can increase the risk of bleeding from the stomach. If aspirin overdose is suspected, seek medical attention for the affected person.
Salicylates, including aspirin, are included in the group of drugs called NSAIDs (nonsteroidal anti-inflammatory drugs). People with asthma and nasal polyps may be hypersensitive to salicylates and other NSAIDs. In addition, use of NSAIDs is not recommended in people with kidney or liver disease, bleeding disorders, other salicylate-containing drugs, and women who are pregnant or breast-feeding.
A breakdown of muscle tissue (rhabdomyolysis) may sometimes occur as a complication of salicylate poisoning.
I’ve heard of Trinder's test for salicylates. What is it?
Should everyone who takes aspirin regularly have a salicylate test performed?
If you take occasional doses for pain, take only one low-dose tablet a day, or take moderate amounts of aspirin under the supervision of your healthcare provider and do not experience any side effects, then it is not typically necessary. Most people will not need to have this test performed unless they accidentally ingest significant quantities of aspirin or another salicylate, or if they develop side effects.
Will taking aspirin at normal dosage cause complications?
Occasional use of aspirin for pain relief at recommended doses usually does not cause complications. It is possible that taking aspirin regularly at higher doses used to treat rheumatoid arthritis, for example, may cause symptoms and other complications, such as an increased risk of bleeding. You should only take aspirin on a regular basis (e.g., daily) under the supervision of a healthcare practitioner. Low-dose aspirin used to reduce the risk of heart attack is generally safe, but even this use should be discussed with a healthcare practitioner.
I am on a low-dose aspirin regimen to prevent another heart attack. Do I need to be monitored with salicylate tests?
No, usually you will not need to be monitored with a salicylate test since the risk of toxicity is low. However, you may be tested to determine whether the treatment to lower your risk of heart attack has been effective using a test that measures platelet function. Aspirin works to prevent blood clots and heart attacks by inhibiting platelet activation and/or clumping (aggregation). Platelet function tests are sometimes used to monitor anti-platelet therapy, including aspirin. For more on this, see the article on Platelet Function Tests.
Why should aspirin not be given to children?
An association has been found between the use of aspirin to treat the symptoms of flu-like viral illnesses such as the chickenpox and the development of Reye syndrome, a disease marked by acute brain damage and liver dysfunction that can be fatal. Aspirin should never be given to children unless directed by a healthcare practitioner. The National Reye's Syndrome Foundation, the U.S. Surgeon General, the Food and Drug Administration, the Centers for Disease Control and Prevention, and the American Academy of Pediatrics all recommend against the use of aspirin or other products containing aspirin to treat fever-causing illnesses in children under the age of 19 years.
How is a salicylate overdose treated?
Anyone who is showing signs of salicylate poisoning should be taken to the emergency room. There is no antidote available for this type of overdose, so treatment is aimed at slowing and/or stopping further absorption of the drug while increasing elimination from the body. The type and extent of treatment is based on the severity of the poisoning.
- If an overdose occurred and it is suspected that some of the drug is still in the stomach, activated charcoal (sometimes several doses) may be given. This absorbs any residual drug and prevents it from being further absorbed into the body.
- Bicarbonate may be given to correct acid-base and electrolyte imbalances. A solution containing bicarbonate might be given intravenously (IV) to promote elimination of the drug through the urine by increasing pH of the urine.
- Other medicines may be given to help treat symptoms.
- Hemodialysis is more commonly used in cases of chronic poisoning/toxicity.