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Acetaminophen

Item Value
Test Update Information Acetaminophen assay changed from the Abbott Axsym method to the Beckman DxC method on 6/25/2012.
Approval req'd? No
Available Stat? Yes
Test code AAPH
Performed by Parnassus Chemistry
In House Availability Test available 24 hours per day 7 days per week
Method Turbidimetric inhibition immunoassay (Beckman DxC800)
Container type Gold top or Light Green top
Amount to Collect 1 mL blood
Sample type Serum
Preferred volume 0.5 mL serum
Min. Volume 0.2 mL serum
Units mg/L
Normal range
Therapeutic 10-20 mg/L
Toxic > 150 mg/L (4 hours post ingestion)
Critical value > 50 mg/L
Synonyms Tylenol; Datril
Stability Room temperature 8 hours, refrigerated 2 days, frozen 1 week
Turn around times STAT 1 hour, Routine 1-3 days
Additional information In suspected intoxication, at least 4 hours must have elapsed post-ingestion before a serum level can assist in determining the need to initiate N-acetylcysteine therapy; earlier levels are uninterpretable for this purpose. For additional emergency information, you may call the San Francisco regional poison center, 1-800-876-4766 (from UCSF dial 47-28600)

Note: some monoclonal proteins may cause falsely low acetaminophen results. The presence of human anti-mouse antibodies or heterophile antibodies may also interfere with the acetaminophen assay in some cases. Testing for acetaminophen levels in parallel dilution studies and with a different assay may be useful in cases where interference by a monoclonal protein or abnormal immunoglobulin is suspected.
LOINC code 3298-7
Last Updated 6/20/2012 1:50:19 PM
Entry Number 5
Image caption Nomogram: acetaminophen plasma concentration vs. time after acetaminophen ingestion (adapted from Rumack BH, Matthew H. Acetaminophen poisoning and toxicity. Pediatrics. 1975;55;871-876, with permission). The nomogram has been developed to estimate the probability of whether a plasma acetaminophen concentration in relation to the interval post ingestion will result in hepatotoxicity and, therefore, whether N-acetylcysteine therapy should be administered.

CAUTIONS FOR USE OF THIS CHART:

Time coordinates refer to time post ingestion. Graph relates only to plasma concentrations following a single, acute overdose ingestion. The Treatment Line is plotted 25% below the Rumack-Matthew Line to allow for potential errors in plasma acetaminophen assays and estimated time from ingestion of an overdose.
Image see image caption
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