Comparison of Urine and Serum Testing for Early Detection of Acetaminophen Ingestion

Acetaminophen is a common ingestant that is routinely screened for, with serum testing, after overdoses. We compared a modified, qualitative, colorimetric, o-cresol urine test for acetaminophen with the standard laboratory serum immunoassay. Twenty-nine adult volunteers were given 975 mg of acetaminophen, and then serum and urine samples were tested at predefined intervals for up to 4 hours. The presence of acetaminophen in the urine samples was determined with a modified o-cresol assay by two independent reviewers and was verified by using high-performance liquid chromatography. Compared with the acetaminophen serum immunoassay, the acetaminophen urine test had specificity of 97% (95% confidence interval, 80-100%) and sensitivity of 100% (95% confidence interval, 81-100%) at 45 minutes. Further studies to improve and to accelerate processing of the qualitative colorimetric o-cresol urine test could allow the test to be used in specific military and civilian clinical scenarios.