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Background: The management of patients with acetaminophen (APAP) toxicity is largely informed by the blood concentration. We sought to assess the analytical characteristics of past and current commercial APAP assays in the United States. Methods: We systematically reviewed the analytical characteristics of APAP assays cleared by the Food and Drug Administration's (FDA) 510(k) premarket notification process by searching the Clinical Laboratory Improvement Amendments (CLIA) database. We collected the following data where available: test principle, precision near 10 mg/L, precision near 150 mg/L, limits of detection, and limits of quantitation. Results: For all assays, absolute analytical precision decreased as analyte concentration increased. Near [APAP] = 10 mg/L, the most precise assays had a standard deviation (SD) of 0.2 mg/L or coefficient of variation (CV) of 1% and the least precise assays had a SD of 1.8 mg/L or a CV of 10%. Near [APAP] = 150 mg/L, the most precise assay had a SD of 1.4 mg/L or CV of 0.9% and the least precise assays had a SD of 7.4 mg/L or a CV of 4.9%. Conclusions: Commercially available APAP assays had good analytical precision with improvement over time. The failure of some manufacturers to validate precision near treatment thresholds is concerning. Newer APAP assays can measure a wider range of [APAP], which likely improves the risk stratification of overdose patients but also carries a risk of overdiagnosis when minuscule quantities are detected. [ABSTRACT FROM AUTHOR]