UMEM Educational Pearls

Category: Toxicology

Title: Utility of Pre-4 Hour Acetaminophen Levels

Keywords: acetaminophen, Rumack-Matthew nomogram (PubMed Search)

Posted: 12/7/2013 by Bryan Hayes, PharmD (Emailed: 12/12/2013) (Updated: 12/12/2013)
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Can acetaminophen concentrations < 100 mcg/mL obtained between 1-4 hours after acute ingestion accurately predict a nontoxic 4-hour concentration? NO!

Despite a high negative predictive value, a new study found there are still cases with toxic concentrations after 4 hours despite earlier levels < 100 mcg/mL. 

The Rumack-Matthew nomogram is to be utilized starting at 4 hours after an acute acetaminophen ingestion. Unless the concentration is zero, a second level must be drawn at 4 hours if an earlier one is positive.


Froberg BA, et al. Negative predictive value of Acetaminophen concentrations within four hours of ingestion. Acad Emerg Med 2013;20(10):1072-5. [PMID 24127715]

Rhyee SH. Early serum acetaminophen levels: how soon is too soon? Acad Emerg Med 2013;20(10):1070-1. [PMID 24127714]

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