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Test Code Billings Clinic: 4051 Acetaminophen, Plasma or Serum

Important Note

Venipuncture should occur prior to Metamizole (Sulpyrine) administration due to the potential for falsely elevated results.

Performing Laboratory

Billings Clinic Laboratory: Chemistry

Useful For

This test is intending for the quantitative determination of acetaminophen in human plasma or serum.



Specimen Requirements

Submit only 1 of the following specimens:

  • Date and time of last dose and date and time of draw are required on request form for processing.
  • Indicate plasma on request form.
  • Label specimen appropriately (plasma or serum).
  • Send refrigerated
  • For therapeutic drug monitoring, first specimen should be drawn at least 4 hours after ingestion of acetaminophen to ensure that peak levels have been achieved.
  • Second specimen should be drawn 2 to 4 hours later.
  • If time of ingestion is unknown, first specimen should be drawn upon presentation, and second specimen drawn 2 to 4 hours later.


  • Draw blood in a green-top (lithium heparin) tube(s).
  • Spin down and send 1 mL of heparinized plasma.


  • Draw blood in a plain, red-top tube(s) or a serum gel tube(s).
  • Spin down and send 1 mL of serum.



Specimen Type Temperature Time
Serum, Plasma Refrigerated (preferred) 2 weeks
  Frozen 45 days


Reference Values

Therapeutic Range:  10.0 - 20.0 µg/mL


Call-back toxic concentration value: >40.0 µg/mL

Toxicity: A single determination is of little value. Serum half-life is the best toxicity indicator and should be <2-3 hours. Hepatic damage is likely if half-life exceeds 4 hours or if serum level is >150.0 µg/mL at 4 hours after ingestion or >40.0 µg/mL at 12 hours.


Day(s) Test Set Up


Test Classification and CPT Coding


LOINC Code Information

Reporting Name LOINC Code
Acetaminophen 3298-7