Lactate Dehydrogenase (LDH)

Function

Lactate dehydrogenase (LDH) is an enzyme found in nearly all living cells. It plays a critical role in cellular respiration, the process by which glucose from food is converted into energy for the cells. Specifically, LDH catalyzes the conversion of lactate to pyruvate and back, as it converts NAD+ to NADH and back. Although LDH is abundant in tissue cells, under normal conditions, only small amounts are found in the blood. When tissues are damaged or diseased, they release LDH into the bloodstream.

Why it is Ordered

Physicians order an LDH test to identify the presence and location of tissue damage in the body. It serves as a general marker of cellular injury. It is frequently used to monitor progressive conditions such as hemolytic or pernicious anemias, to help stage certain cancers (like lymphoma or leukemia), and to evaluate fluid buildup (effusions) in the lungs or heart. It is a non-specific marker, meaning it tells a doctor that damage is occurring, but not exactly where or what caused it.

Associated Conditions

High levels of LDH are associated with a wide array of conditions because of the enzyme's ubiquitous nature. These include:

• Myocardial Infarction (Heart Attack): Historically used to detect heart damage, though troponin is now preferred.
• Liver Disease: Such as hepatitis or cirrhosis.
• Hemolytic Anemia: Where red blood cells are destroyed prematurely.
• Pulmonary Infarction: Tissue death in the lungs.
• Cancer: Including germ cell tumors, lymphoma, and leukemia.
• Muscle Trauma: Severe injury or muscular dystrophy.