Human Phenotype Ontology id HP_0045040 (Abnormal circulating lactate dehydrogenase concentration) is a deviation from the normal serum concentration/activity of lactate dehydrogenase (LDH), which catalyzes the reduction of pyruvate to form lactate. Also known as: Abnormal LDH level, Abnormal circulating LDH concentration, Abnormal lactate dehydrogenase level, AbnormalLDH level.