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Lactate dehydrogenase, commonly known as LDH, is an enzyme found in nearly all body tissues. It plays a crucial role in energy production by helping convert sugar into energy that cells can use. When cells are damaged or destroyed, LDH is released into the bloodstream, making it a useful marker for detecting tissue damage. A blood test measuring LDH levels can help healthcare providers identify and monitor various medical conditions, including liver disease, heart attack, certain cancers, and blood disorders.

The LDH test is performed using a simple blood sample drawn from a vein, typically in the arm. No special preparation is usually required, though your healthcare provider may ask you to fast for a certain period before the test in some cases. The blood sample is then sent to a laboratory where technicians measure the amount of LDH present. Normal LDH levels can vary slightly depending on the laboratory and the specific method used, but generally range from about 140 to 280 units per liter for adults. Levels outside this range may indicate tissue damage or disease.

Elevated LDH levels can result from many different conditions because the enzyme is present in so many tissues throughout the body. High levels may indicate liver disease such as hepatitis or cirrhosis, heart conditions including heart attack or heart failure, muscle diseases, certain types of anemia, lung diseases, pancreatitis, or various cancers including lymphoma and leukemia. Strenuous exercise, certain medications, and even hemolysis of the blood sample during collection can also cause temporarily elevated results. Because LDH is not specific to one particular organ or condition, doctors typically use it alongside other tests to make an accurate diagnosis.

There are five different forms of LDH, called isoenzymes, which are found in different tissues. LDH-1 is primarily found in the heart and red blood cells, LDH-2 in white blood cells, LDH-3 in the lungs, LDH-4 in the kidneys and pancreas, and LDH-5 in the liver and skeletal muscles. In some cases, healthcare providers may order an LDH isoenzyme test to determine which specific form is elevated, helping to pinpoint the source of tissue damage more precisely. This additional testing can provide valuable information for diagnosis and treatment planning.

The LDH test is often used not only for initial diagnosis but also for monitoring disease progression and response to treatment, particularly in cancer patients. Regular LDH measurements can help doctors assess whether a treatment is working or if the disease is advancing. While an elevated LDH level alone does not provide a specific diagnosis, it serves as an important piece of information that, when combined with other clinical findings and test results, helps healthcare providers make informed decisions about patient care.