Lactate dehydrogenase (LDH) is an enzyme found in nearly all body cells, playing a role in cellular energy production. This protein facilitates metabolic reactions fundamental for normal cell function. While present in low amounts in the bloodstream, increased levels can indicate damaged or injured cells or tissues. Measuring LDH levels through a blood test serves as a general indicator of tissue damage.
The Role of LDH in the Body and Cancer
Lactate dehydrogenase functions as a catalyst in anaerobic glycolysis, a metabolic pathway cells use to produce energy when oxygen is limited. This enzyme converts pyruvate into lactate, a process that also regenerates NAD+. The regeneration of NAD+ allows glycolysis to continue, ensuring a steady supply of adenosine triphosphate (ATP) for cellular activities even in low-oxygen environments.
Cancer cells often exhibit a unique metabolic shift, known as the Warburg effect, where they preferentially rely on glycolysis for energy production, even when oxygen is abundant. This rapid energy generation supports their fast growth. The increased glycolytic activity within tumors leads to an overproduction of lactate, leading to increased LDH activity to manage this byproduct. When cancer cells grow rapidly or die, they release their intracellular contents, including LDH, into the bloodstream, causing elevated levels.
Interpreting LDH Test Results
Elevated LDH levels are a non-specific indicator, meaning they signal general tissue damage but do not pinpoint the exact cause or location of the injury. Many non-cancerous conditions can lead to an increase in circulating LDH. For instance, various heart conditions, such as a heart attack, can release LDH from damaged cardiac muscle cells.
Many non-cancerous conditions can also lead to increased LDH:
Liver diseases like hepatitis or cirrhosis, due to liver cell injury.
Blood disorders, particularly hemolytic anemia, where red blood cells are prematurely destroyed and release LDH.
Muscle injuries, such as strenuous exercise or trauma.
Conditions affecting the kidneys or lungs.
Certain infections, including meningitis, encephalitis, mononucleosis, and HIV.
LDH as a Prognostic and Monitoring Tool in Oncology
Lactate dehydrogenase levels are not used to diagnose cancer due to their non-specific nature; an elevated level alone does not confirm a cancer diagnosis. Instead, the LDH test primarily applies in oncology once a cancer diagnosis is established. Its value lies in providing insights into a patient’s prognosis and monitoring treatment effectiveness over time.
At the time of diagnosis, very high LDH levels can correlate with a larger tumor burden or a more aggressive form of the disease, which can influence the overall prognosis. For example, in non-small cell lung cancer, elevated pretreatment LDH is considered an independent adverse prognostic marker. Monitoring LDH levels throughout treatment can help assess how well therapies are working; a consistent decrease in LDH often indicates a favorable response to treatment, suggesting that the tumor is shrinking or responding to therapy. Conversely, persistently rising LDH levels during or after treatment may suggest that the cancer is not responding well, has progressed, or has recurred. LDH is commonly used as a marker in specific cancers, including lymphomas, leukemia, melanoma, and testicular cancer, where its levels can provide valuable information for clinical management.