The Lactic Dehydrogenase (LDH) test is a blood test that measures the level of the enzyme lactate dehydrogenase in your blood. Lactate dehydrogenase (LDH) test is used to help detect tissue damage or disease in the body,  because LDH is released into the bloodstream when cells are damaged or destroyed. LDH is found in many body tissues, including the heart, liver, kidneys, muscles, brain, and blood cells. When any of these tissues are injured, LDH levels can increase.