MedCalcHub stores your favorites, history, and saved calculations locally in your browser using localStorage. This data never leaves your device.
Optional advertising, when enabled, may use third-party cookies or similar technologies. You can accept or reject advertising below.
Determines whether N-acetylcysteine (NAC) treatment is indicated following a single acute acetaminophen (paracetamol) ingestion, based on the serum acetaminophen concentration and time since ingestion.
Treatment threshold (mcg/mL) = exp(5.3325 − 0.0805 × hours since ingestion). Valid for 4–24 hours post single acute ingestion.
Below treatment line
The Rumack-Matthew nomogram was published in 1975 (Pediatrics 55:871-876) and is the standard tool for determining NAC treatment in acute acetaminophen ingestion in the United States. The nomogram uses a semi-log plot of serum acetaminophen concentration versus time since ingestion, with a treatment line derived from reported cases of hepatotoxicity. The treatment line represents the minimum acetaminophen level associated with potential hepatotoxicity at each time point.
Specialty
Emergency MedicineCategory
EmergencyDifficulty
Basic
Estimated Time
30 seconds
Version
1.0
Last Updated
2026-08
Formula
Keywords
Normal Range
Below treatment line
| Classification | Range |
|---|---|
Below treatment line | Level < threshold at given time |
Above treatment line | Level ≥ threshold at given time |
Determines whether N-acetylcysteine (NAC) treatment is indicated following a single acute acetaminophen ingestion, based on the serum acetaminophen concentration and time since ingestion.
Level at or above treatment threshold: Initiate NAC therapy. Level below treatment threshold: NAC not indicated for single acute ingestion with known timing. The nomogram is valid only for 4–24 hours post-ingestion.
The Rumack-Matthew nomogram is the standard tool for determining NAC treatment in acute acetaminophen overdose in the United States. Early NAC treatment is highly effective at preventing hepatotoxicity when initiated within 8 hours of ingestion.
A patient ingested a single acute dose of acetaminophen. At 6 hours post-ingestion, the serum level is 120 mcg/mL.
Inputs:
Treatment threshold at 6h ≈ 130 mcg/mL. Level 120 mcg/mL is BELOW the threshold — NAC not indicated for this single acute ingestion.
The Rumack-Matthew nomogram is a graphical tool that plots serum acetaminophen concentration against time since ingestion. A treatment line defines the threshold above which N-acetylcysteine (NAC) treatment is recommended to prevent hepatotoxicity.
The nomogram is applicable ONLY for a single acute ingestion (one time ingestion) with a KNOWN time of ingestion. It is valid for serum levels obtained 4 to 24 hours after ingestion. It does NOT apply to repeated ingestions, chronic use, or staggered ingestions.
If the time of ingestion is unknown, the nomogram cannot be used. In this case, obtain acetaminophen level, hepatic function tests (AST, ALT, INR), and renal function. Treat with NAC if there is any concern for toxicity, and consult toxicology.
Levels obtained before 4 hours post-ingestion may not have peaked and are unreliable for ruling out toxicity. Repeat the level at 4 hours or later. If there is clinical concern, start NAC and recheck.
The nomogram is not validated for sustained-release formulations. For sustained-release ingestion, consider prolonged monitoring and consult toxicology, as peak levels may be delayed.
Disclaimer: This calculator is intended for educational and clinical decision support. For acetaminophen overdose, always consult clinical toxicology and follow institutional protocols. This calculator does not replace clinical judgment.
Determining NAC treatment in single acute acetaminophen ingestion.
Only applicable for single acute ingestion with known timing, 4–24 hours post-ingestion.
Assessing liver disease severity once hepatotoxicity has developed.
Does not guide initial NAC treatment decisions in acetaminophen overdose.