Paracetamol level

Keywords: Acetaminophen level

Specimen:

5 mL blood in plain tube collected, ideally 4 h after ingestion of the paracetamol.

A second specimen collected at least 2 h later can be used to measure paracetamol half-life.

Method:

Spectrophotometry, chromatography, or immunoassay.

Reference Interval:

Toxic range: > 1,300 µmol/L (195 mg/L) 4h after ingestion of paracetamol.

Paracetamol half-life:

< 4 h: low probability of liver damage

> 12 h: hepatic coma likely.

Application:

Assessment of toxic overdose.

Interpretation:

See Figure 2.

Toxicity is more likely and occurs at lower plasma levels in patients with pre-existing liver disease.

Calculation of half-life (from two specimens) is also a useful guide to hepatotoxicity as prolongation of half-life is a good predictor of the risk of development of acute hepatocellular damage.

Reference:

Dargan PI and Jones AL. Trends Pharmacol Sci 2003; 24(4): 154-157.