Lactate dehydrogenase (LDH) is an enzyme that helps your body produce energy and is found in almost every cell, including the heart, kidneys, liver, and muscles. A blood test measures the amount of LDH in your bloodstream. While elevated LDH levels can be associated with some types of cancer, a high reading does not automatically mean a cancer diagnosis. Many other conditions can cause LDH to increase, as it is a non-specific marker of general tissue damage.
Understanding Lactate Dehydrogenase (LDH)
Lactate dehydrogenase is a protein that speeds up a chemical reaction in your body’s cells. This reaction is a step in anaerobic metabolism, the process cells use to convert glucose into energy when oxygen is low. Because LDH is present throughout the body, an elevated level is not specific to one condition. When cells are damaged by illness or injury, they release LDH into the bloodstream. This causes the concentration of LDH in the blood to rise above the normal range of 140 to 280 units per liter (U/L) for adults, signaling tissue damage without indicating the cause.
Non-Cancerous Causes of Elevated LDH
A wide array of conditions unrelated to cancer can cause an increase in LDH levels, as any event that leads to cell or tissue damage is a potential cause.
Common non-cancerous causes include:
- Strenuous physical exercise or significant muscle injuries.
- Heart attacks, which lead to the death of heart muscle cells.
- Liver diseases such as hepatitis or cirrhosis.
- Kidney disease.
- Blood disorders like hemolytic anemia, where red blood cells are destroyed prematurely.
- Infections such as infectious mononucleosis, meningitis, and HIV.
- Certain medications, including aspirin and narcotics.
The Relationship Between High LDH and Cancer
There is a relationship between elevated LDH and certain cancers, stemming from the unique metabolic needs of cancer cells. Tumors often grow so rapidly that they outstrip their blood supply, creating a low-oxygen, or hypoxic, environment. In these conditions, cancer cells rely heavily on the anaerobic energy production pathway that LDH facilitates, leading them to produce more of the enzyme. As a tumor grows, some of its cells die and break apart, a process known as cell turnover, releasing large amounts of LDH into the bloodstream.
For this reason, LDH is considered a non-specific tumor marker that indicates widespread cell damage but cannot confirm a cancer diagnosis on its own. Instead, physicians use LDH levels as a prognostic tool. In cancers like lymphoma, leukemia, melanoma, and testicular cancer, a higher LDH level can suggest a larger tumor burden or a more aggressive disease. Doctors may also monitor LDH levels during treatment; a decrease can indicate that the therapy is working, while a rising level might suggest the cancer is not responding.
What to Expect After a High LDH Test Result
Receiving a high LDH test result can be unsettling, but it is important to remember that it is an initial finding, not a diagnosis. Your doctor will interpret the result within the context of your overall health, including your medical history, physical exam findings, and any symptoms you may be experiencing. The first step is often to repeat the test to confirm the finding, as factors like strenuous exercise or how the blood sample was handled can cause a temporary or false elevation.
If the level remains high, your physician will likely order further tests to identify the source of the tissue damage. To narrow down the possibilities, a doctor might order an LDH isoenzyme test. This test breaks down the total LDH into five different subtypes, each of which is concentrated in different tissues. For example, high levels of LDH-1 and LDH-2 may point toward the heart, while elevated LDH-5 is often associated with the liver.
Depending on these results and your symptoms, imaging studies like a CT scan or MRI might be used to look for organ damage or tumors. If a specific area of concern is identified, a biopsy may be necessary to make a definitive diagnosis.