At a Glance
Why Get Tested?
To determine if an overdose has occurred; to determine risk of liver damage and to help determine if treatment with an antidote is required
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
A blood sample drawn from a vein in the arm
Test Preparation Needed?
The Test Sample
What is being tested?
Acetaminophen is one of the most common pain relievers (analgesics) and fever reducers (antipyretics) available over the counter. It is generally regarded as safe. However, it is also the most common cause of toxic hepatitis in North America and Europe and one of the most common poisonings from either accidental or intentional overdose.
Acetaminophen is primarily processed (metabolized) by the liver. In therapeutic doses, the liver is able to process the drug safely without any harmful effects. When a large dose is ingested and/or when doses exceed the recommended amount over a period of time, however, the liver may be overwhelmed and may not process the excessive amount of drug. As a result, a toxic intermediate form of the drug can build up in the liver and cause damage to liver cells. If treatment is not given soon enough, liver failure may result.
For this reason, acetaminophen can be harmful or even fatal if not taken correctly and children in particular are at risk if caregivers do not follow dosing instructions carefully. Often, people do not realize that acetaminophen is one of the ingredients in many combination medications such as cold and flu preparations. If two or more of these medications are taken together, levels of acetaminophen may exceed safe limits.
Acetaminophen preparations come in varying strengths and several different forms, including tablets, capsules and liquid.
- For adults, the typical maximum daily limit for acetaminophen is 4000 milligrams (mg). Consuming more than 4000 mg in a 24-hour period is considered an overdose, while ingesting more than 7000 mg can lead to a severe overdose reaction unless treated promptly.
- For children, the amount that is considered an overdose depends on their age and body weight. (For more on this, see the MayoClinic webpage Acetaminophen and children: Why dose matters.)
If it is known or suspected that someone has ingested an overdose of acetaminophen, it is recommended to take the person to the emergency room. If a health practitioner determines that an overdose has occurred, treatment may include an antidote, N-acetylcysteine (NAC), which can help minimize damage to the liver, especially if given within 8 to 12 hours after an overdose. Though NAC is ideally administered within this timeframe, people who seek treatment more than 12 hours after ingestion may still be given the antidote.
Until recently, NAC for people who visit healthcare providers later than 24 hours after acetaminophen ingestion was not the standard of care for acetaminophen overdose management in the United States. However, study data from England suggest that NAC may be beneficial for acetaminophen-induced liver failure more than 24 hours after ingestion.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
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.
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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.
Sources Used in Current Review
U.S. Food and Drug Administration. Press release: FDA recommends health care professionals discontinue prescribing and dispensing prescription combination drug products with more than 325 mg of acetaminophen to protect consumers. Available online at http://www.fda.gov/Drugs/DrugSafety/ucm381644.htm through http://www.fda.gov. Released January 14, 2014. Accessed Aug 4, 2014.
MedlinePlus. National Institutes of Health. Acetaminophen. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/meds/a681004.html#brand-names through http://www.nlm.nih.gov. Last reviewed January 1, 2014. Accessed August 3, 2014.
Mayo Clinic. Acetaminophen and children: Why dose matters. Available at http://www.mayoclinic.org/healthy-living/childrens-health/in-depth/acetaminophen/art-20046721 through http://www.mayoclinic.org. Last updated April 13, 2014. Accessed August 4, 2014.
Susan E Farrell and Germaine L Defendi. Acetaminophen Toxicity Workup. Medscape. Available online at http://emedicine.medscape.com/article/820200-workup through http://emedicine.medscape.com. Updated June 24, 2014. Accessed August 4, 2014.
Beauchamp G, et.al. Performance of a Multi-disciplinary Emergency Department Observation Protocol for Acetaminophen Overdose. J Med Toxicol. Sep 2013; 9(3): 235–241. Available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3771000/ through http://www.ncbi.nlm.nih.gov. Accessed September 2014.
(May 7, 2013) Patolia S. Acetaminophen Level. Medscape. Available online at http://emedicine.medscape.com/article/2089664-overview#aw2aab6b2 through http://emedicine.medscape.com. Accessed September 2014.
Sources Used in Previous Reviews
MedlinePlus Medical Encyclopedia. Acetaminophen overdose. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002598.htm. Accessed August 2010.
MedlinePlus Drug Information. Acetaminopen. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/meds/a681004.html. Accessed August 2010.
MayoClinic.com. Acetaminophen. Available online at http://www.mayoclinic.com/health/drug-information/DR601885 through http://www.mayoclinic.com. Accessed August 2010.
ARUP Lab Tests. Acetaminophen. Available online at http://www.aruplab.com/guides/ug/tests/0090001.jsp through http://www.aruplab.com. Accessed August 2010.
Dart, R. et. al. (© 2006). Acetaminophen Poisoning: an Evidence-Based Consensus. Guideline for Out-of-Hospital Management. Clinical Toxicology 44:1-18, 2006 [On-line information]. PDF available for download at http://www.aapcc.org/archive/FinalizedPMGdlns/APAP%20-%20final%20guideline%209.9.05.pdf through http://www.aapcc.org.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 1238-1239.
Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 470-471.
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. St. Louis: Elsevier Saunders; 2006, Pp 1807, 1304-1305.
Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, P. 316.
Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL eds, (2005) Harrison's Principles of Internal Medicine, 16th Edition, McGraw Hill, P. 1840-1841.
Wu, A. and McKay, C., Editors (© 2003). Recommendations For The Use Of Laboratory Tests To Support Poisoned Patients Who Present To The Emergency Department. The National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines, SECTION IV. Recommendations on Laboratory Assays for Other Toxicants as Causes of Poisonings: A. "Universal" acetaminophen and salicylate screening [On-line information]. Available online at http://www.aacc.org/SiteCollectionDocuments/NACB/LMPG/toxicology/emergency_lmpg.pdf#page=28 through http://www.aacc.org. Accessed August 2010.
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 361-364, 684-685.
(Sept 23 2009) Farrell S. Toxicity, Acetaminophen: Treatment and Medication. Medscape article. Available online at http://emedicine.medscape.com/article/820200-treatment through http://emedicine.medscape.com. Accessed August 2010.