The test for acetaminophen is used to measure the level of drug in the blood in order to establish a diagnosis of overdosage, to assess the risk of liver damage, and to help decide on the need for treatment. Prompt diagnosis and treatment are important for a positive outcome. Since high levels of acetaminophen can be toxic to the liver, tests such as AST and ALT may be used to detect liver damage. A PT may be used to detect impaired liver function.
When an overdose of acetaminophen is suspected, a blood level is ordered every 4 to 6 hours after ingestion or after the time that it is thought ingestion occurred. If a blood sample is collected too soon, the test results may not accurately reflect the amount that was absorbed in the stomach and entered the blood. Symptoms can appear as early as 2 to 3 hours after ingestion or may not occur for 12 or more hours. Some of these include:
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. Evidence:
The table below summarizes some results that may be seen:
Acetaminophen LevelResult Interpretation
10-20 mcg/mLTherapeutic levels
Less than 150 mcg/mL 4 hours after ingestionLow risk of liver damage
Greater than 200 mcg/mL 4 hours after ingestion Or Greater than 50 mcg/mL 12 hoursAssociated with toxicity and liver damage after ingestion
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 doctor 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 overuse cases. Evidence:
Be aware that many prescription and nonprescription medications contain acetaminophen in combination with other medications. Do not take more than one medication that contains acetaminophen at a time. If you drink three or more alcoholic beverages each day, ask your doctor 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.
Clinical Pearl is a Continuous professional development platform with a precise and concise point of care clinical knowledge search engine and 360-degree learning cycle management platform for all healthcare professionals and organizations.