The Rumack-Matthew nomogram is a well studied and validated tool to help assess the potential for liver toxicity following acute acetaminophen poisoning.  Here is a brief review of when it is best utilized.

• Prior to 4 hours post-ingestion: Not helpful to determine likelihood for toxicity.  Only use is to confirm an ingestion took place.
• Between 4 and 24 hours post-ingestion: Plot the patient's level vs. time after ingestion.  If above the toxicity line, treat with acetylcysteine.
• More than 24 hours post-ingestion: Any elevated acetaminophen level is toxic and should be treated with acetylcysteine.

Outside-the-box situations:

• Chronic exposures: Nomogram not indicated.
• Overdoses with co-ingestants that slow GI motility (e.g., opioids, diphenhydramine) OR extended release products (e.g., Tylenol Arthritis): If the level at 4 hours post-ingestion is not toxic, repeat it at 8 hours post-ingestion.  If either level is toxic, treat with acetylcysteine.

References