Determination of 14C-labelled ketone bodies by liquid-scintillation counting

1. A method of assaying ¹⁴C in ketone bodies present in blood by using liquid-scintillation counting is described. 2. d(−)-β-Hydroxy¹⁴C]butyrate is converted quantitatively into ¹⁴C]acetoacetate by means of a coupled oxidoreduction reaction involving NAD⁺, d(−)-β-hydroxybutyrate dehydrogenase and malic dehydrogenase in the presence of a high concentration of oxaloacetate. 3. ¹⁴C]Acetoacetate is decarboxylated to acetone and carbon dioxide which are trapped separately in a double-well flask and counted subsequently. 4. The method permits the determination of ¹⁴C activity in the individual ketone bodies and allows the activity in the carboxyl carbon atoms of acetoacetate or of d(−)-β-hydroxybutyrate to be assayed separately from the activity in the remainder of the molecule. 5. Recoveries of ¹⁴C-labelled ketone bodies added to blood approach 100% with good reproducibility in replicate analyses.