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, health 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 health 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.
Health 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
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.
The table below summarizes some results that may be seen:
Less than 150 mcg/mL 4 hours after ingestion
Low risk of liver damage
Greater than 200 mcg/mL 4 hours after ingestion
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 health 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.
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 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.
This article was last reviewed on October 14, 2014. | This article was last modified on October 14, 2014.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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