ENZYMATIC METHOD FOR DETERMINING KETONE-BODY RATIO IN ARTERIAL BLOOD

We have developed a new, sensitive, and rapid method for measuring the ketone body concentration in arterial blood and determining the arter ial blood ketone body ratio. The procedure involves the sequential use of the enzymes 3-hydroxybutyrate dehydrogenase (3-HBDH; EC 1.1.1.30) and NADH oxidase, followed by a color-generating reaction with the hyd rogen peroxide produced by the oxidase reaction. The amount of oxidize d chromogen produced is proportional to the 3-hydroxybutyrate (3-HBA) concentration. The acetoacetate (AcAc) concentration is obtained after complete conversion of the AcAc to 3-HBA, in the presence of 3-HBDH. The total 3-HBA concentration is measured and then subtracted from the total ketone body concentration to give the AcAc concentration. This procedure may be applied to plasma samples and the absorbance change m easured with an automated chemistry analyzer. Ketone body concentratio n may be determined over the range 0 to 400 mu mol/L. The analysis tak es similar to 12 min and requires only 30 mu L of plasma.