What is the Rumack–Matthew nomogram?

The **Rumack–Matthew nomogram** is a clinical tool published in 1975 that uses a patient's *serum acetaminophen level* and *time since ingestion* to determine whether hepatotoxicity risk is high enough to warrant treatment with *N-acetylcysteine (NAC)*.

At what level does acetaminophen require treatment?

Using the standard treatment line: **150 µg/mL at 4 hours post-ingestion**, declining to *4.69 µg/mL at 24 hours*. The threshold at intermediate time points is interpolated logarithmically. Levels above the treatment line at any time point require NAC.

Can the nomogram be used for paediatric patients?

The nomogram thresholds are the same for adults and children. However, *paediatric acetaminophen toxicity cases should always involve a toxicologist or specialist*, as risk factors and NAC dosing differ from adults.

Why is the nomogram not valid before 4 hours?

Before 4 hours, *absorption may still be ongoing* and the serum level may not yet have peaked. An early low level does not rule out significant toxicity — the level could rise substantially as absorption continues. The nomogram only applies to levels drawn at or after *4 hours post-ingestion*.

What is N-acetylcysteine (NAC) and how does it work?

**N-acetylcysteine (NAC)** is the antidote for acetaminophen toxicity. It works by replenishing hepatic *glutathione*, which is depleted by the toxic acetaminophen metabolite NAPQI. When started within 8 hours of ingestion, it effectively *prevents hepatic injury* in the vast majority of cases.

Is the nomogram valid for extended-release acetaminophen?

**No.** Extended-release formulations have a different absorption profile. A level drawn at 4 hours may not reflect the peak concentration. Levels should be repeated at *4–6 hours after the initial reading* and specialist advice sought for all extended-release overdoses.

Toxicology · Rumack–Matthew Nomogram

Acetaminophen Nomogram
Calculator

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Acetaminophen Toxicity — Rumack–Matthew Nomogram

Educational reference only · Last reviewed: March 2026

This tool plots a serum acetaminophen level against the Rumack–Matthew nomogram to estimate whether N-acetylcysteine (NAC) treatment may be indicated.

The nomogram is only valid for: single, acute overdoses at a known time of ingestion, with a level drawn between 4 and 24 hours post-ingestion.

It is not valid for staggered/repeated ingestions, unknown ingestion time, or chronic excess ingestion.

Always contact your regional poison centre or clinical toxicology service and follow local guidelines before making treatment decisions. This tool must not be used as the sole basis for clinical care.

I understand this is educational only and will confirm all treatment decisions with clinical toxicology / poison centre.