The causes of high lactate dehydrogenase in children include the following: First, it is caused by damage to the heart muscle cells. Viral myocarditis is caused by viral infections in children, and when the myocardium is damaged, the lactate dehydrogenase level is high. An increase in creatine kinase isoenzyme can better confirm the diagnosis of high lactate dehydrogenase due to myocardial damage in children. Second, it is caused by damage to the liver cells. If a child has liver cell damage, such as hypoxia or hepatitis B virus infection, these causes can lead to liver cell damage and increase in lactate dehydrogenase.