L-Lactate Dehydrogenase B Chain (LDH-B) is a member of the lactate dehydrogenase family that consists of three members, LDH-A, LDH-B and LDH-C; members of this family function as powerful markers for germ cell tumors. LDH-B is an oxidoreductase that catalyzes the interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD+. It converts pyruvate to lactate when oxygen is absent or in short supply and it performs the reverse reaction during the Cori cycle in the liver. It is also called Hydroxybutyrate Dehydrogenase (HBD) due to its ability to catalyze the oxidation of hydroxybutyrate.