Salicylate (Blood)

Does this test have other names?

Salicylate serum test, serum salicylate level test, serum salicylate concentration test

What is this test?

This is a blood test to check for salicylate intoxication, which is usually caused by an overdose of aspirin. This test is also used to check for the correct aspirin dose in people who are given high doses of aspirin to treat inflammation from arthritis.

Aspirin contains acetylsalicylic acid, or ASA. Other salicylates are found in some wart removers, antidiarrhea medication, medicines for bloating, and some Chinese herbal medicines. Methyl salicylate, for example, is found in a Chinese medicine called oil of wintergreen. One teaspoon contains the equivalent of 22 adult aspirin tablets.

Aspirin poisoning can happen in children, but it's less common now because the drug is packaged in child-resistant containers. Also, aspirin can cause Reye's syndrome in children and teens. Reye's syndrome is a potentially life-threatening condition, so aspirin should never be given to children.

Aspirin poisoning is still a concern, however, because some teens and adults take too much aspirin on purpose. Each year U.S. regional poison control centers log about 20,000 cases of salicylate exposure among children and teens.

Severe salicylate intoxication can be fatal. Taking too much aspirin, for example, overwhelms your body's usual means of protection against poisoning. Your system may start shutting down, and you may lapse into a coma.  

Why do I need this test?

You may have this test if it's possible you have overdosed on aspirin or other products containing salicylates. Signs of an overdose include:

  • Rapid heartbeat

  • Abnormally deep or rapid breathing

  • Fever

  • Increased heart rate

  • Tinnitus or ringing ears

  • Vertigo or dizziness

  • Diarrhea

  • Vomiting

  • Nausea

  • Too much acid in your bodily fluids

In addition, severe aspirin toxicity can alter how your brain functions and how you think. Symptoms include:

  • Confusion

  • Agitation

  • Seizures

  • Restlessness

  • Coma, although this is rare

This test is required to confirm a diagnosis of aspirin intoxication. You may have this test every two hours to monitor your blood levels. It's likely you will have this test until two tests in a row show that the concentration of aspirin in your blood is lower than the peak measurement.

This test is also used to monitor how well treatment of the intoxication is working and to find out whether more dramatic treatment measures are needed. For example, results of this test can tell whether you need hemodialysis, a procedure that uses a machine to clear your blood of toxins. 

What other tests might I have along with this test?

You may have other tests to look at your salicylate toxicity level. These include:

  • Arterial blood gas, to look for acid-base balance

  • Electrolytes and glucose tests

  • Urinalysis, to watch the progress of the poisoning

  • Plasma creatinine, to find out whether you have kidney failure

  • Electrocardiogram

  • Toxicology screen

  • Coagulation tests

  • Acetaminophen level, because some products contain both salicylate and acetaminophen

  • Pregnancy test

  • Imaging studies

Your health care provider may also give you a physical exam and take your health history. 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

If your doctor prescribed aspirin for inflammation or arthritis, the typical level of aspirin is between 10 to 30 milligrams per deciliter (mg/dL) of blood. Any concentration above 40 mg/dL can be toxic.

In adults, taking 10 to 30 grams of aspirin can be fatal. Children may be fatally poisoned by as little as 3 grams of aspirin. Because aspirin usually comes in tablets that contain 81 mg or 325 mg, this would be as few as nine tablets! 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

Too many blood fats, or lipids, can interfere with test results. But lab workers may remove any extra lipids from your sample through a process called lipemia.

How do I get ready for this test?

You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.