Kinetic assay of beta-hydroxybutyrate in plasma with a COBAS-BIO centrifugal analyzer

An enzymic rate method for measuring beta-hydroxybutyrate in plasma by use of beta-hydroxybutyrate dehydrogenase (EC 1.1.1.30) was adapted to the Roche COBAS-BIO centrifugal analyzer. Optimum reagent composition and reaction conditions were determined, to provide increased sensitivity and accuracy. Use of magnesium ions increased sensitivity. Comparison of results with those of a manual enzymic endpoint method involving perchloric acid protein-free filtrates of whole blood showed excellent correlation (r = 0.996). The method has good within-run and day-to-day precision. Linearity of the standard curve extends to 5000 mumol of beta-hydroxybutyrate per liter. The assay can be completed in less than 5 min and requires 15 microL of plasma and minimal reagent volumes.