To determine if an overdose has occurred and if an antidote is required; to determine risk of liver damage and to help monitor the outcome of antidote treatment
Acetaminophen
Acetaminophen
Also Known As
Paracetamol
This article was last reviewed
on
This article waslast modified
on November 16, 2020.
At a Glance
Why Get Tested?
When To Get Tested?
When it is suspected that a person has ingested an overdose of acetaminophen or has signs and symptoms of toxicity, such as nausea, vomiting, and abdominal pain; when following a patient, every 4 to 6 hours after an overdose of the drug is ingested
Sample Required?
A blood sample drawn from a vein
Test Preparation Needed?
None
Accordion Title
Common Questions
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How is the test used?
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When is it ordered?
Healthcare practitioners may order acetaminophen levels beginning at 4 hours after ingestion or possible ingestion and then every 4 to 6 hours to monitor whether the drug level is increasing or decreasing. Samples collected too soon after ingestion may not accurately reflect the amount absorbed from the stomach into the blood.
Testing may be ordered when a person has signs and symptoms of an overdose. These can appear as early as 2 to 3 hours after ingestion or may not occur for 12 or more hours. Some of these include:
- Nausea, vomiting, diarrhea
- Loss of appetite
- Abdominal pain or cramping
- Irritability
- Sweating
If untreated, toxicity can progress within 3 to 4 days to include jaundice, liver and kidney failure, convulsions, coma and death. If treatment is received within 8 hours of the overdose, however, there is a very good chance of recovery.
For children who have taken acetaminophen in liquid form, a treatment decision may be made as soon as 2 hours after ingestion since the drug is absorbed more rapidly in this form.
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What does the test result mean?
The table below summarizes some results that may be seen:
Acetaminophen Level Result Interpretation 10-20 mcg/mL Therapeutic levels Less than 150 mcg/mL 4 hours after ingestion Low risk of liver damage Greater than 200 mcg/mL 4 hours after ingestion Or
Greater than 50 mcg/mL 12 hours after ingestion
Associated with toxicity and liver damage The levels discussed above typically apply to a single ingestion of a toxic amount of the drug. They do not necessarily apply to cases in which the recommended amount of acetaminophen has been exceeded over a period of time (chronic overdose ingestion). However, a healthcare practitioner may take acetaminophen levels into account along with clinical signs and symptoms and liver tests to determine the risk and/or presence of liver damage in chronic overdose cases.
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Is acetaminophen dangerous if used appropriately?
Acetaminophen is one of the safest, most effective drugs known if used at the recommended dose and dose interval.
Children, particularly those under 6 years of age, are at risk of accidental overdose if caregivers do not follow dosing instructions carefully. However, the reported incidence for children are not as common as in adults. Deaths are typically only seen in cases involving multi-drug combinations.
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How is an acetaminophen overdose treated?
Anyone who is showing signs of acetaminophen poisoning should be taken to the emergency room. If it is established that an overdose occurred, the person may be given an antidote (N-acetylcysteine or NAC), which is most effective if given within the first 8 hours following ingestion. The person may also receive other medicines to help treat symptoms.
If it is suspected that some of the drug is still in the stomach (usually within 4 hours after ingestion), the person may be given activated charcoal, which absorbs any residual drug and prevents it from being absorbed into the body. Within about 1 hour of ingestion, someone may receive gastric lavage. It involves pumping liquid, usually water or saline, into the stomach and suctioning the liquid and other stomach contents out through a tube.
Sometimes extensive liver damage occurs despite treatment with the antidote N-acetylcysteine. If liver failure results after an overdose, a liver transplant may be necessary.
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In addition to acetaminophen levels, what other lab tests might be done?
Since high levels of acetaminophen can be toxic to the liver, healthcare practitioners may also order tests such as AST and ALT to detect liver damage. A PT may be used to detect impaired liver function. A healthcare practitioner might also order serum salicylate levels or a urine drug screen for unconscious patients or those for whom there is a suspicion of ingestion of other substances. Other possible tests include blood gases, lactate level, and metabolic panel with creatinine. These are used to monitor severity of liver failure and, in cases of severe overdose, determine whether an overdose patient would benefit from liver transplantation.
Women of childbearing age who have suspected acetaminophen overdose may get human chorionic gonadotropin (hCG) tests to determine if they are pregnant because the drug crosses the placenta and can harm the fetus.
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Is there anything else I should know?
Acetaminophen is the most common drug ingredient for medicines used in the U.S., including over-the-counter medicines for cold and the flu, allergies and sleeplessness. Consumers can buy many products containing acetaminophen without a prescription. Accidental overdose may happen when multiple medications containing acetaminophen are used simultaneously, resulting in a total combination dose that exceeds the maximum safe limits, especially for those with liver diseases and excessive alcoholic consumption.
If you drink three or more alcoholic beverages each day, ask your healthcare provider if you should take acetaminophen. If you will be taking more than the occasional 1 or 2 doses of acetaminophen, do not drink alcohol as this may increase the chance of liver damage.
It is important for you to tell your physicians, dentists and other healthcare providers about all the medications you are taking so that accidental overdose due to combination use can be avoided.