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Test Code ACMA Acetaminophen, Serum

Useful For

Monitoring toxicity in overdose cases

Method Name


Reporting Name

Acetaminophen, S

Specimen Type


Specimen Required

Serum gel
Red top
Specimen Volume:
0.5 mL
Collection Instructions:
1. Serum gel tubes should be centrifuged within 2 hours of collection.
2. Red-top tubes should be centrifuged and aliquoted within 2 hours of collection.

Specimen Minimum Volume

0.25 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 14 days
  Frozen  28 days
  Ambient  14 days

Reject Due To


Mild OK; Gross reject







Clinical Information

Acetaminophen (found in Anacin-3, Comtrex, Contac, Datril, Dristan, Excedrin, Nyquil, Sinutab, Tempera, Tylenol, Vanquish, and many others) is an analgesic, antipyretic drug lacking significant anti-inflammatory activity. It is metabolized by the liver with a normal elimination half-life of less than 4 hours. In normal therapeutic doses, a minor metabolite, possessing electrophilic alkylating activity, readily reacts with glutathione in the liver to yield a detoxified product. In overdose situations, liver glutathione is consumed and the toxic metabolite (postulated metabolite: benzoquinone) reacts with cellular proteins resulting in hepatotoxicity, characterized by centrilobular necrosis, and possible death, if untreated. N-acetylcysteine can substitute for glutathione and serves as an antidote.


Serum concentration and half-life are the only way to assess degree of intoxication in early stages since other liver function studies (eg, bilirubin, liver function enzymes) will not show clinically significant increases until after tissue damage has occurred, at which point therapy is ineffective.


Therapeutic concentration: <30 mcg/mL


Normal half-life: <4 hours


Toxic concentration: >150 mcg/mL


Toxic half-life: >4 hours


The toxic level is dependent on half-life. When the half-life is 4 hours, hepatotoxicity generally will not occur unless the concentration is greater than 150 mcg/mL. The level at which toxicity occurs decreases with increasing half-life until it is encountered at values as low as 50 mcg/mL when the half-life reaches 12 hours.


For half-life determination, draw 2 specimens at least 4 hours apart and note the exact time of each draw. Half-life can be calculated from the concentrations and the time interval.


First specimen should be drawn no sooner than 2 hours postingestion.

Clinical Reference

Rumack BH, Peterson RG: Acetaminophen overdose: incidence, diagnosis, and management in 416 patients. Pediatrics Nov 1978;62:898-903

Method Description

Acetaminophen is hydrolyzed by an arylacylamidase to yield p-aminophenol andacetate. Subsequently the p-aminophenol is converted to an indophenol in the presence of o-cresol and a periodate catalyst. The production of indophenol is followed colorimetrically. The change in absorbance is directly proportional to the quantitative drug concentration in the sample.(Package insert: Roche Acetaminophen reagent, Roche Diagnostic Corp, Indianapolis, IN)

Day(s) and Time(s) Performed

Monday through Sunday; Continuously

Analytic Time

Same day/1 day

Specimen Retention Time

1 week

Performing Laboratory

Mayo Medical Laboratories in Rochester

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
ACMA Acetaminophen, S 3298-7


Result ID Test Result Name Result LOINC Value
ACMA Acetaminophen, S 3298-7

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

Reference Values

Therapeutic: <30 mcg/mL

Toxic: >150 mcg/mL 4 hours after dose