Clinical evaluation of an acetaminophen meter for the rapid diagnosis of acetaminophen intoxication. STUDY OBJECTIVES: To test the accuracy of a newly developed meter that determines serum acetaminophen concentration after a 30-second analysis of one drop of whole blood. DESIGN: Sixty-six blood samples from patients with known or suspected drug overdose were analyzed for the presence of acetaminophen. In all cases determination of serum acetaminophen concentration was performed simultaneously with the meter and by a reference laboratory. SETTING: Eligible patients were those who presented during a nine-month period to the emergency departments of two tertiary care hospitals (including a pediatric hospital). RESULTS: Thirty-one specimens had a laboratory-confirmed detectable acetaminophen concentration. The meter identified these toxic specimens in all cases; there were no false-negatives (sensitivity, 100%). Among the 35 specimens not containing acetaminophen, the meter invariably confirmed a nondetectable serum acetaminophen concentration (specificity, 100%). Acetaminophen measurements by the meter correlated strongly with laboratory determinations (r = .985, P less than .001). Repeated testing of one specimen documented the precision and reproducibility of the meter's analysis; mean coefficient of variation was .08 in measuring toxic acetaminophen concentrations. Drug coingestion had no significant effect on the accuracy of the meter. Instrument accuracy was maintained after more than 100 uses without recalibration. CONCLUSIONS: This meter identifies the possibility of rapid and accurate determinations of serum acetaminophen concentration. The instrument is ideally suited for patients with acetaminophen poisoning in whom expeditious and appropriate administration of antidotal therapy is desired. 