Acetaminophen (Rumack-Matthew) nomogram

For a single acute acetaminophen ingestion with a known time, the level 4–24 hours after ingestion is compared with the US treatment line (150 mcg/mL at 4 hours, halving every 4 hours).

What goes into the Acetaminophen nomogram

Hours since ingestion (4–24) (h)
Acetaminophen level (mcg/mL)

How to interpret the result

On or above the line: start N-acetylcysteine
Below the line: NAC not needed for a single acute ingestion with a reliable time
Level ≥ 2× the line: higher-risk ingestion; discuss NAC dosing with poison control

Clinical pearls

Not valid for staggered ingestions, unknown time, chronic supratherapeutic use, or before 4 hours.
Extended-release products or co-ingested anticholinergics or opioids: repeat the level 4–6 hours later.
If in doubt, start NAC; it is safe and most effective within 8 hours.
Call poison control: 1-800-222-1222 (US).

Evidence

Rumack BH, Matthew H. Acetaminophen poisoning and toxicity. Pediatrics. 1975;55:871-876.
Dart RC, et al. Management of acetaminophen poisoning in the US and Canada: a consensus statement. JAMA Netw Open. 2023;6:e2327739.

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Acetaminophen overdose

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For education only. Check the inputs and the population the score was validated in before acting on it. Not a substitute for clinical judgment.