Laboratory Testing in Acetaminophen Overdose

Initial Laboratory Panel

The American Association for the Study of Liver Diseases recommends ordering baseline AST, ALT, INR, creatinine, BUN, electrolytes, and blood glucose immediately in suspected acetaminophen overdoses, with a strength of evidence based on expert opinion 1
Baseline labs, including hepatic function (AST and ALT), coagulation status (INR), renal function (creatinine and BUN), and metabolic status (blood glucose and electrolytes), are critical for predicting outcome and guiding treatment decisions, according to the Hepatology society 1

The American College of Emergency Physicians suggests monitoring AST, ALT, and INR every 4 hours until aminotransferases peak and begin declining, with a moderate strength of evidence based on observational studies 1, 2
INR monitoring every 4 hours identifies evolving coagulopathy, which predicts severe hepatotoxicity, as recommended by the Hepatology society 1

Very high aminotransferases (>3,500 IU/L) are highly correlated with acetaminophen poisoning and should prompt consideration of this diagnosis, even without clear ingestion history, according to the Hepatology society 1

If the patient develops signs of acute liver failure, expand monitoring to include phosphate, as hypophosphatemia is common in severe cases, with a strength of evidence based on case series 2