When you have symptoms such as nausea, rapid breathing, ringing in the ears (tinnitus), or confusion that may be from taking too much aspirin or medications with salicylate ingredients; when it is suspected that your child may have ingested a significant quantity of a salicylate; at regular intervals when monitoring an overdose; sometimes on a regular basis if you take a salicylate on prescription for rheumatoid arthritis or another autoimmune disorder
A blood sample taken from a vein usually in an arm
None, but your doctor may ask when you last took a salicylate and the amount taken. If you regularly take a prescription salicylate, your doctor may want to collect blood just prior to your next dose (trough level). Tell your doctor about any other 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).
Aspirin is the most common salicylate, but there are others, including methyl salicylate, which is found as oil of wintergreen in some muscle ache creams. Methyl salicylate creams and topical forms of aspirin are absorbed into the body through the skin. After oral forms of salicylates are ingested, they are converted to salicylic acid, absorbed in the stomach and small intestine and transferred into the blood stream.
With single, normal doses, blood concentrations typically reach a maximum 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 ingested at one time (acute toxicity) or too much is taken over a period of time (chronic toxicity), and/or if the body's ability to remove the salicylates is reduced, then signs and symptoms associated with toxicity will begin to emerge. The ability to remove salicylates efficiently is affected by the body's blood and urine pH (acidity/alkalinity) and by kidney function.
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 are at risk. Aspirin may also be used to reduce the risk of complications in someone who is having a heart attack, or who has recently experienced one. Aspirin is also used in patients with myeloproliferative neoplasms (e.g. polycythaemia vera, essential thrombocythaemia). Aspirin is now rarely used to relieve symptoms of rheumatoid arthritis (RA) and osteoarthritis as well as symptoms of autoimmune disorders such as systemic lupus erythematosus.
When used with care and following dosing directions, therapeutic doses of salicylates are safe and effective for most adults. Excessive amounts of salicylates, however, can be toxic, affecting breathing and disrupting the body's acid-base balance. In severe cases, toxicity can cause convulsions, coma, and even death.
Adults can experience problems with salicylate toxicity when they unknowingly combine multiple products that contain them. Many over-the-counter medications include a salicylate as one of the ingredients. An individual who is unaware of the ingredients 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 someone has pain that is not relieved with an initial dose and, unaware of the danger, takes more than the recommended dose and/or takes additional doses too frequently. In the elderly, these scenarios can especially be a problem because underlying conditions and general health status can decrease the ability to eliminate salicylates.
Aspirin is not recommended for use in children and adolescents (under 16) because of the risk of developing Reye’s syndrome, a disease characterized by acute brain damage and liver dysfunction that can be fatal. Though young people are not routinely given aspirin, they may become poisoned through accidental or intentional ingestion. Topical creams that contain methyl salicylate or other salicylates are of special concern as they contain very high doses.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed, but the doctor may ask when a salicylate was last ingested and the amount taken. To accurately interpret results, blood samples are usually collected at least 4 hours after ingestion. If you regularly take a medication containing a high dose of salicylate, the doctor may want to collect blood just prior to the next dose (trough level).
How is it 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) or to monitor someone who takes a high dose of salicylate.
If a person presents with symptoms that suggest aspirin or other salicylate poisoning, then a salicylate blood test may be requested to help detect an overdose. If a doctor is not sure what substance(s) a person may have ingested, then a salicylate test may be requested along with other tests associated with emergency and overdose drug testing. The specific tests requested will depend upon the person's symptoms and clinical signs.
In emergency situations, a salicylate test may be requested with other tests, such as:
- Arterial blood gases and electrolytes to evaluate blood oxygen capacity and acid-base balance
- Blood urea and creatinine to evaluate kidney function
- Urinalysis to monitor urine pH
- Glucose to detect low blood sugar
- Liver function tests
If a toxic concentration of salicylate is detected, then a series of salicylate blood tests (and some of the additional tests) may be requested to determine whether the salicylate level has increased, or has peaked and started to drop. This information is used to help monitor the person's health status and help guide treatment.
A salicylate test may be used to monitor for an overdose if an individual regularly takes high doses of salicylate, such as to relieve the symptoms of rheumatoid arthritis, osteoarthritis, or systemic lupus erythematosus, or to treat rheumatic fever or Kawasaki disease, although other non-steroidal anti-inflammatory drugs are now usually preferred in these conditions. Monitoring may be particularly necessary if the person's other medications, or health status, have changed. Salicylate monitoring is usually not necessary for individuals taking low-dose aspirin . This may be particularly necessary if the person's other medications, or health status, have changed.
Monitoring is usually not necessary for individuals taking low-dose aspirin (75 mg/day) to lower the risk of blood clots (thrombosis), heart attack, or stroke (see Common Questions, What does the test result mean? and Do I need to be monitored with salicylate tests?).
When is it requested?
Salicylate testing may be requested when it is suspected that someone has ingested a large amount of aspirin or other drugs containing salicylate. Usually, blood is collected and tested at least 4 hours after last known ingestion. Results from tests done earlier than this are difficult to interpret, as the drug may still be being absorbed from the stomach and gastrointestinal tract.
Testing may be requested when a person is experiencing symptoms associated with an acute or chronic salicylate overdose. Symptoms may include:
- Nausea and vomiting
- Hyperventilation (rapid breathing)
- Ringing in the ears (tinnitus)
Additional symptoms that may develop include:
- Rapid heart rate
- Overheating (hyperthermia), especially in young children with severe toxicity
- Shortness of breath due to fluid accumulation in the lungs (pulmonary oedema)
- Bleeding (less common)
When acute salicylate toxicity is detected, a doctor may request the test as frequently as every 2-3 hours to monitor the progress of the overdose, as the drug may still be being absorbed from the intestines (see Common questions - 'bezoars’ , Is there anything else I should know?)
When an individual is taking regular doses of a prescribed salicylate, a doctor may request this test on a routine basis to check for an elevated level, as toxicity may develop without obvious signs and symptoms. Someone with chronic salicylate toxicity may have symptoms that develop slowly and are nonspecific, such as confusion, nausea, rapid heart rate, and fever, and these may be seen with many other conditions. A salicylate test may be done to help determine whether salicylate toxicity is the cause of the symptoms.
When salicylate is not prescribed, then identifying chronic salicylate toxicity can sometimes be more challenging. After questioning a patient, a doctor may request a salicylate level as part of a number of tests to help determine the cause of the symptoms.
What does the test result mean?
Normal therapeutic concentrations of aspirin and other salicylates depend upon what the drug is being used for, and blood levels must be interpreted in conjunction with the medical history and 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 emerge, 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 100-300 mg/L (0.7 – 2.2 mmol/L). In general, the severity of salicylate toxicity increases with increasing concentrations. The table below summarizes some results that may be seen in a blood sample that is collected at least 4 hours after the last dose:
Salicylate result (mg/L) Salicylate result (mmol/L) Result Interpretation 20-100 0.1-0.7 Therapeutic level for pain relief (analgesia) 100-300 0.7-2.2 Anti-inflammatory level; some symptoms of toxicity may appear, such as headache, tinnitus, vertigo More than 300 More than 2.2 Symptoms of toxicity increasingly frequent
Rising levels (when a person has not taken more salicylate) indicate that salicylate is still being absorbed and peak concentrations have not yet been reached. Falling salicylate levels usually indicate that the excess is being eliminated by the body and that the overdose is resolving.
Salicylate toxicity is a rare but serious condition that requires hospitalization and careful monitoring. In severe cases, the body’s acid-base balance may be disturbed, and this may - worsen over time Salicylate may also cause electrolyte imbalances, low blood sugar, and dehydration, proceeding to convulsions, hallucinations, delirium, and coma.
Is there anything else I should know?
Be aware that many prescription and nonprescription medications contain salicylates in combination with other medications. Always read the label, and do not take more than one medication that contains salicylates at the same time.
With large doses of salicylate, accumulations of the tablets (sometimes called bezoars) may form in the digestive tract. This can cause the drug to continue to be absorbed for some time, increasing blood levels even though the person has not ingested more of the drug.
Aspirin should not be taken long-term without consulting a doctor and should NEVER be given to children under 16 unless directed by a doctor. It should not be taken by patients with active peptic ulcers, or anyone with haemophilia or another bleeding disorder. Aspirin should not be taken with alcoholic drinks as this can increase the risk of bleeding from the stomach. If aspirin overdose is suspected, medical attention should be sought immediately. Ibuprofen (Nurofen) or paracetamol (Panadol) are safer treatments than aspirin for short-term problems such as headache. Other non-steroidal anti-inflammatory drugs such as ibuprofen or naproxen are preferable in rheumatoid arthritis.
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 doctor and do not experience any side-effects, then testing is usually not 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 on regular treatment.
Will taking aspirin at normal dosage cause complications?
Occasional use of aspirin for pain relief at recommended doses in adults usually does not cause complications, except in susceptible individuals. It is possible that taking aspirin regularly at the doses used to treat rheumatoid arthritis, for example, may cause symptoms and may cause complications such as an increased risk of bleeding. Regular aspirin consumption should only be adopted under the supervision of your doctor. Low-dose aspirin (75 mg/day) used to reduce the risk of heart attack is generally safe, but even this use should be discussed with your doctor.
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, or an INR test to monitor blood clotting. Aspirin works to prevent blood clots and heart attacks by inhibiting platelet activation and/or clumping (aggregation). Platelet function tests or the INR test are sometimes used to monitor anti-platelet therapy, including aspirin.
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 chickenpox and the development of Reye’s syndrome, a disease characterized by acute brain damage and liver dysfunction that can be fatal. Aspirin should never be given to children under 16 unless directed by a doctor.
How is a salicylate overdose treated?
Anyone who is showing signs of salicylate poisoning should be taken to Accident and Emergency. There is no antidote available for this type of overdose, so treatment is aimed at preventing further absorption of the drug while increasing elimination from the body. The type and extent of treatment is based on the severity of toxicity. If it is established that an overdose has occurred and if it is suspected that some of the drug is still in the stomach, the patient may be given activated charcoal (sometimes several doses), which absorbs any residual drug and prevents it from being absorbed into the body. The patient may also be given bicarbonate to correct acid-base and electrolyte imbalances. A solution containing bicarbonate might be given intravenously to increase elimination of the drug in the urine. Other medicines may be given to help treat symptoms. In very severe cases, dialysis may be performed to remove the drug from the blood.