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Do negative levels at one hour rule out paracetamol ingestion?

Three Part Question

In [a patient presenting to the emergency department following a drug overdose] does [a negative paracetamol level at one hour post ingestion][rule out paracetamol ingestion sufficient to necessitate treatment?]

Clinical Scenario

A 45 year old woman presents to the emergency department one hour after taking eight ibuprofen tablets. She denies co-ingestion. You are happy with her medical condition, but concerned about her mental state, and so request a psychiatric review. However, the psychiatric doctor refuses to see her until she is proven to need no treatment for paracetamol poisoning. As this will take another three hours, you wonder if a sample drawn now, would, if it contained no paracetamol, exclude a significant overdose, thus expediting referral.

Search Strategy

Ovid MEDLINE 1966 to February week 2 2006
Ovid EMBASE 1980 to Week 8 2006
Medline: [emergency mp. OR emergencies] AND [poisoning mp. OR poisoning OR overdose mp. OR overdose] AND [paracetamol mp. OR acetaminophen] LIMIT to human and English language.
Embase: [emergency mp. OR emergency medicine OR emergency treatment OR emergency] AND [poisoning mp. OR intoxication] AND paracetamol mp. OR paracetamol glucuronide OR paracetamol sulfate OR paracetamol derivative OR paracetamol] LIMIT to human and English language.

Search Outcome

Altogether,132 papers were identified via medline, and 139 via embase, none of which were directly relevant to the study question.


There is no literature on the relevance of negative paracetamol levels at one hour in the context of patients presenting to the emergency department shortly following an overdose.

Clinical Bottom Line

There is no current evidence to prove that a negative paracetamol level at one hour in a patient who has taken a drug overdose is sufficient to exclude significant paracetamol ingestion. Local advice should be followed.