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Test Code LAB4000 ACETAMINOPHEN LEVEL

Important Note

Useful for:

  • Monitoring toxicity in overdose cases

Synonyms

Tylenol, APAP, Acephen, Excedrin, Anacin-3, Datril, Phenacetin

Specimen Type

Preferred Specimen: Lithium Heparin Plasma (Light Green Top Tube)

Alternative Specimens: Serum (SST, Gold, Tiger, Red Top Tube)

Collection Instructions

Draw peak specimen 1 hour post IM dose or 1/2 hour post IV infusion.

Specimen Volume

Preferred: 1 mL

Minimum: 0.5 mL

Specimen Processing

Centrifuge tube ASAP.

Clinical Information

Acetaminophen (paracetamol) is an analgesic. Therapeutic doses rarely cause adverse side effects, but chronic excess has been shown to cause hepatotoxicity and nephrotoxicity. Acute overdose with acetaminophen can cause hepatic damage which can lead to liver failure if not treated. Treatment must begin within 8 hours of ingestion to lessen the potential for hepatic injury; therefore, early detection of acetaminophen in the blood stream is important. Toxicity is usually reported at concentrations over 150 µg/mL at 4 hours and 4.7 µg/mL at 24 hours. Acetaminophen toxicity is treated with N-acetylcysteine as an antidote and other intensive support care.

Method

Enzymatic/Colorimetric

 

Acetaminophen in the sample is hydrolyzed by the enzyme aryl acylamidase to p-aminophenol and acetate. The p-aminophenol reacts with the 2,5-dimethylphenol in the presence of a manganese catalyst to create the chromophore 4-(4-iminophenol)-2,5-dimethylcyclohexadiene-1-one. This reaction is measured at 660 nm and is proportional to the concentration of acetaminophen in the sample.

Turnaround Time

STAT: 1 hour
Routine: 4 hours

Limitations

  • For serum and urine specimens and assasy that are colorimetric or an immunoassay:
    • High bilirubin (>50 ug/mL) may cause false-positive with immunoassay-based tests.
  • Do not use whole blood
  • Interferences from medication or endogenous substances may affect results.
  • Samples containing paraproteins (particularly IgM) may cause unreliable and artificially elevated results in patients with Waldenstrom macroglobulinemia.

Test Schedule

Daily and STAT

Sample Stability

Room Temp: 24 hours
Refrigerated: 24 days
Frozen: 50 days (-20C)

Reference Ranges

Acetaminophen µg/mL

Normal:  Less than 30 µg/mL

Critical: >150 µg/mL

  • Normal therapeutic doses of acetaminophen result in serum concentrations of 10-30 µg/mL in healthy adults.
  • Toxicity is generally reported at concentrations over 150 µg/mL at 4 hours and 4.7 µg/mL at 24 hours, which is considered the possible toxicity line. 

CPT Codes

80143

Test Components

Acetaminophen, µg/mL.

Measuring Range 3 µg/dL – 377 µg/mL

Reporting Limits 3 µg/dL – 3770 µg/mL

If result after a 1:10 dilution is greater than 3770 µg/mL, report out >3770 µg/mL.

Critical Range

>150 µg/mL

IMO Code

IMO-PROC-30991892