Lactate dehydrogenase (LDH) is an enzyme found in nearly all cells of the body, playing a role in energy production. When cells are damaged or destroyed, LDH is released into the bloodstream. This makes LDH a general indicator of tissue damage, and its levels can be elevated in various conditions, including certain types of cancer. Understanding how cancer influences LDH levels offers insights into disease activity and potential treatment responses.
Understanding Lactate Dehydrogenase
Lactate dehydrogenase is an enzyme that facilitates a critical step in cellular energy production within glycolysis. This process converts glucose into pyruvate, and in the absence of sufficient oxygen, LDH then converts pyruvate into lactate. This reaction regenerates NAD+, which is necessary for glycolysis to continue, ensuring a supply of energy even when oxygen is scarce.
LDH exists in different forms, called isoenzymes, each predominating in various tissues throughout the body. For instance, LDH-1 is primarily found in the heart and red blood cells, while LDH-5 is more prevalent in the liver and muscles. These isoenzymes’ presence across tissues highlights LDH’s widespread involvement in metabolism and its release upon cellular injury or death.
How Cancer Influences LDH Levels
Cancer cells often exhibit a unique metabolic characteristic known as the “Warburg effect,” or aerobic glycolysis. Unlike normal cells that primarily use oxygen for efficient energy production, cancer cells frequently rely on glycolysis, even when oxygen is plentiful. This metabolic shift results in an increased conversion of glucose to lactate, even in the presence of oxygen.
This heightened production of lactate involves LDH, as the enzyme catalyzes the conversion of pyruvate to lactate. The increased activity of LDH supports the rapid growth and proliferation of cancer cells. Furthermore, as tumors grow and some cancer cells die, they release their contents, including LDH, into the bloodstream, contributing to elevated levels.
Measuring LDH in Cancer Care
Measuring LDH levels is a straightforward process, performed through a blood test. A healthcare professional draws a blood sample, which is then sent to a laboratory for analysis. The amount of LDH in the sample is measured and reported in units per liter (U/L) or international units per liter (IU/L).
Normal reference ranges for LDH can vary slightly between different laboratories. For adults, they typically fall between 135 to 280 U/L. Children usually have higher normal LDH levels than adults. When reviewing results, it is important to refer to the specific reference range provided by the testing laboratory.
What Elevated LDH Indicates
While elevated LDH levels are not exclusively indicative of cancer, they can provide significant information when observed in a cancer patient. High LDH levels may suggest a larger tumor burden, meaning the tumor is more extensive or aggressive. This correlation is due to the increased metabolic activity of rapidly dividing cancer cells and the release of LDH from damaged or dying tumor cells.
Elevated LDH levels are often associated with a less favorable prognosis in many cancers. This has been observed in various malignancies, including non-Hodgkin lymphoma, melanoma, and testicular cancer. For instance, in small-cell lung cancer, patients with normal LDH levels at diagnosis often have a better survival outcome than those with elevated levels. It is important to remember that many non-cancerous conditions, such as liver damage, heart attack, muscle injury, or severe infections, can also cause elevated LDH, so the results are always interpreted in the context of a patient’s overall clinical picture.
LDH as a Tool in Cancer Treatment
Doctors frequently utilize LDH levels throughout the cancer treatment journey to guide medical decisions. At the time of initial diagnosis, LDH levels are often assessed as part of a baseline workup to help determine the extent or aggressiveness of the disease. This initial measurement provides a reference point for future comparisons.
During treatment, monitoring LDH levels can help assess how well therapy is working. A decrease in LDH levels often indicates that the cancer is responding to treatment, suggesting tumor shrinkage or reduced activity. Conversely, if LDH levels begin to rise after treatment completion, it might signal a recurrence of the disease, prompting further investigation. The baseline LDH level or changes in its concentration can also influence the choice or intensity of therapy.