UMEM Educational Pearls

Title: Does a low initial APAP level after an acute APAP overdose useful in identifying ED patient who will not require NAC?

Keywords: acetaminophen overdose, APAP levels (PubMed Search)

Posted: 12/8/2016 by Hong Kim, MD, MPH (Updated: 12/9/2016)
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Question

Recent study evaluated whether an acetaminophen (APAP) level obtained less than 4-hour post acute ingestion can predict which patient would not require n-acetylcysteine (NAC). APAP cutoff level of 100 ug/mL was used for analysis. This was a secondary analysis of the Canadian Acetaminophen Overdose Study database (retrospective study).

Bottom line:

If initial APAP level of 100 ug/mL was applied as a cutoff point, it missed 27 patients (N= 1821) who had toxic APAP level at > 4-hour post ingestion that require NAC.
Only a very low (< 15 ug/mL) or undetectable initial APAP reliably identify (sensitivity 100%) patients who do not require NAC.
Absorption of APAP can be delayed by coingestion of opioids or antimuscarinics.

Answer

Table 2. Diagnostic accuracy of acetaminophen concentration obtained 2 to 4 hours post-ingestion to identify subsequent potentially toxic concentration measured 4 to 20 hours pos-ingestion.

	Subsequent 4-hour equivalent [APAP]
[APAP] obtained 2 to 4 hours post-ingestion	>150 ug/mL	< 150 ug/mL
<10	0	89
10-20	2	79
20-50	6	209
50-100	19	249
100-150	46	253
150-200	161	195
200-300	276	46
300-450	148	5
>450	38	0

References

Yarema MC, et al. Can a serum acetaminophen concentration obtained less than 4 hours post-ingestion determine which patients do not rquire treatment with acetylcysteine? Clin Toxicol 2016; online early: doi: 10.1080/15563650.2016.1247959