Toxic levels of acetaminophen produce a major positive interference on Glucometer Elite and Accu-chek Advantage glucose meters.

ied this possibility by performing the enzymatic assay on controls containing increasing concentrations of ACET in the presence of different therapeutic concentrations of NAC (Fig. 1A). Evidently, NAC concentrations $100 mg/L cause a marked negative bias, reaching total suppression of the reaction in the presence of 10 g/L NAC. In contrast, similar concentrations of NAC have no effect on the ACET TDx immunoassay (Fig. 1B). According to the TDx method manual, concentrations of up to 1000 mg/L NAC cause only a minimal bias of ,1 mg/L ACET in this assay. Plasma concentrations of NAC after administration of the common initial dose of 150 mg/kg of body weight over a period of 15 min have been reported to range from 304 to 875 mg/L (5). NAC concentrations in this range, and certainly the higher concentrations of blood NAC reached after larger dosages during infusion, markedly impede ACET determination by the enzymatic assay (Fig. 1A). That the drug of choice for treating ACET intoxication produces a very large negative bias in a commonly used enzymatic-colorimetric assay of ACET is worth noting. On the basis of the present observation, we recommend that patients’ blood should be sampled for ACET before the initiation of NAC treatment. Alternatively, enzyme-based colorimetric methods should be replaced by immunoassays or HPLC assays of ACET in which NAC causes no interference.