The lactate dehydrogenase (LDH)-serum test is a blood test that measures the level of LDH in the bloodstream. LDH is an enzyme found in many tissues throughout the body, including the heart, liver, kidneys, and muscles. When tissue damage or injury occurs, LDH is released into the bloodstream. Therefore, the LDH-serum test can be used as a general marker of tissue damage or disease. Elevated levels of LDH may indicate a variety of conditions, such as liver disease, muscle injury, heart attack, cancer, and infections. However, since LDH is not a specific marker for any one particular disease, further testing and evaluation are usually required to determine the underlying cause of elevated LDH levels.