Lactate, Pyruvate, Acetoacetate, and 3-Hydroxybutyrate

Lactate, pyruvate, acetoacetate, and 3-hydroxybutyrate are intermediary metabolites that physiologically occur in blood and play an essential role in energy production. Their relative blood concentrations are an expression of nutritional balance, providing a view of the metabolic disturbances arising in a patient. This chapter presents the principles of the methods available for the determination of these compounds and describes their clinical significance in various pathological conditions. Lactate is a metabolite which plasma level reflects the equilibrium between its production and consumption by different tissues. Hyperlactatemia can be observed in ischemic conditions or in many inherited metabolic diseases. Due to pyruvate instability in blood, deproteinization of blood samples has to be performed immediately after sampling. Determination of pyruvate, always associated with lactatemia, is helpful for the diagnosis of pyruvate dehydrogenase deficiency where hyperlactatemia is associated with hyperpyruvatemia and, pyruvate carboxylase deficiency where hyperlactatemia is not associated with hyperpyruvicemia. Ketone bodies circulate in the blood as 3-hydroxybutyrate and acetoacetate. Their blood concentration depends on the equilibrium between production by the liver (ketogenesis) and consumption at the peripheral level (ketolysis). Abnormalities of ketone body metabolism can present as ketosis, hypoketotic hypoglycemia, and 3OHB/AA ratio inversion.