Acetaminophen, Plasma, NIH Units

CPT CODE:

  • 82003

USEFUL FOR:

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

SPECIMEN REQUIRED:

Draw blood in a lavender-top (EDTA) tube(s).  Spin down and send1.0 mL of EDTA plasma.

TRANSPORT TEMPERATURE:

Refrig\Ambient OK\Frozen OK

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 <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: N-Acetyl-Imidoquinone) 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.

CLINICAL INTERPRETATION:

-  Therapeutic concentration:  <50 mg/L-  Normal half-life: <4 hours- Toxic concentration:  120 mg/L-  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 120 mg/L.      -  The level at which toxicity occurs decreases with increasing          half-life until it is encountered at values as low as 50 mg/L          when the half-life reaches 12 hours.

REFERENCE VALUES:

Therapeutic concentration:  <50 mg/L

Toxic concentration:  > or = 120 mg/L

Half-life:  <4 h

Toxic half-life:  >4 h

 

The toxic level is dependent on half-life. When the half-life is 4 h,

hepatotoxicity generally is not seen until the concentration is greater

or equal to 120 mg/L. The level at which toxicity occurs decreases

with increasing half-lives until it is encountered at values as low as

50 mg/L when the half-life reaches 12 h.