Homogeneous enzyme immunoassay of acetaminophen in serum

A new commercially available homogeneous enzyme immunoassay, using the glucose-6-phosphate dehydrogenase (G6PDH) catalyzed conversion of NAD to NADH, has been evaluated and applied to the determination of acetaminophen in serum. Replicate analysis of serum control samples over the range of 10-200 micrograms/mL demonstrated a within-assay coefficient of variation of less than or equal to 4.6% and a between-assay coefficient of variation of less than or equal to 5.8%. Regression analysis of two separate groups of 98 and 47 serum samples by this technic, using different reagent lots, and a HPLC reference method gave equations of y = 0.981x - 0.941 (r = 0.984) and y = 1.06x - 2.21 (r = 0.994), respectively. No interference due to hemolysis or turbidity was noted. Evaluation of samples containing 35 commonly prescribed or over the counter medications demonstrated no significant cross-reactivity. Prepared reagents were stable over a period of at least 2 months when stored at 4 degrees C. Correlations between two reagent lots were excellent (r = 0.998). A single sample can be analyzed expeditiously. The result may help evaluate a potential acetaminophen poisoning. Another way to assess this toxicity, calculation of the elimination half-life, has limitations that depend on the precision of the analysis.