What is the role of liver function tests (LFTs) in the workup of acetaminophen toxicity/poisoning)?

Updated: Jan 17, 2020
  • Author: Susan E Farrell, MD; Chief Editor: Michael A Miller, MD  more...
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Obtain liver function tests (LFTs). Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) concentrations begin to rise within 24 hours after an acute ingestion and peak at about 72 hours. In severe overdose, transaminase elevation can be detected as early as 12-16 hours post-ingestion. Toxicity is defined as serum AST or ALT concentrations greater than 1000 IU/L. A rapid progression of transaminase values to 3000 IU/L or greater reflects severe hepatotoxicity. Include bilirubin and alkaline phosphatase concentrations.

A proposed strategy for predicting hepatotoxicity involves multiplying the acetaminophen concentration times the ALT concentration. [27] Products and risk levels are as follows:

  • < 1500 - Low risk
  • 1500-10,000 - Low to moderate risk
  • > 10,000 - High risk

However, rises in ALT tend to be late events, which may limit the usefulness of this strategy in less severe overdoses. [28]

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