Use of a competitive inhibitor in a kinetic enzymatic method for measuring ethanol in serum

We describe a kinetic enzymatic method for ethanol in serum, based on the use of pyrazole, a competitive inhibitor for alcohol dehydrogenase (EC 1.1.1.1). The method is rapid and is easily automated for the Cobas Bio centrifugal analyzer. No specimen pretreatment is necessary and the total reaction time is 120 s. The standard curve is linear up to 140 mmol/L. The within-run CV was between 1.9% and 3.5%; the between-run CV ranged from 2.6% to 4.1%. Mean analytical recovery of ethanol added to serum was 100.2%. We compared results of the kinetic enzymatic method with those from a gas-liquid chromatographic (GLC) method and another commercial alcohol dehydrogenase method (TDx REA Ethanol; Abbott Diagnostics). Linear regression analysis gave the following equations: kinetic = 0.991GLC - 0.354 mmol/L (r = 0.992, n = 110) and kinetic = 0.998TDx - 1.741 mmol/L (r = 0.993, n = 70). No interference from methanol or isopropanol was seen.