Lactate Dehydrogenase (LDH) – Enzyme & Lab Value
Lactate dehydrogenase (LDH) is an enzyme found in nearly all body cells and plays a key role in energy metabolism. Elevated LDH levels in the blood can indicate tissue damage or disease.
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Lactate dehydrogenase (LDH) is an enzyme found in nearly all body cells and plays a key role in energy metabolism. Elevated LDH levels in the blood can indicate tissue damage or disease.
What is Lactate Dehydrogenase?
Lactate dehydrogenase (abbreviated LDH) is an enzyme present in almost all human cells. It plays a central role in cellular energy metabolism, particularly in the conversion of lactate (lactic acid) to pyruvate and vice versa. This process is a key part of anaerobic glycolysis, the production of energy without oxygen.
LDH exists in five distinct forms known as isoenzymes (LDH-1 through LDH-5), which are found in varying concentrations across different organs and tissues. For example, LDH-1 is predominantly found in the heart muscle and red blood cells, while LDH-5 is mainly present in the liver and skeletal muscle.
Medical Significance and Clinical Use
Under normal conditions, LDH is primarily found inside cells. However, when cells are damaged or die, LDH is released into the bloodstream. For this reason, measuring LDH in the blood serves as a general marker for tissue damage or cell death.
LDH measurement is used as part of routine blood tests and is an important component of laboratory diagnostics. Elevated levels can indicate a wide range of medical conditions.
Causes of Elevated LDH Levels
An elevated LDH level in the blood is not specific to any single condition but is a general sign of cellular damage. Possible causes include:
- Heart attack: The death of heart muscle cells releases LDH into the blood.
- Liver disease: Hepatitis, liver cirrhosis, or drug-induced liver damage.
- Pulmonary embolism: Impaired blood flow in the lungs can raise LDH levels.
- Blood disorders: Anemias (e.g., hemolytic anemia), leukemias, and lymphomas.
- Muscle conditions: Muscle injuries, intense physical exertion, or inflammatory muscle diseases (myositis).
- Kidney disease: Kidney infarction or severe kidney damage.
- Cancer: Many types of cancer are associated with elevated LDH levels, making LDH a useful tumor marker.
- Infections: Severe infections such as COVID-19 can raise LDH levels significantly.
Reference Values and Diagnosis
The reference range for LDH in the blood varies depending on the laboratory and measurement method, but typically falls between 120 and 240 U/L (units per liter) in adults. Values outside this range should always be interpreted in the appropriate clinical context.
To determine which organ is affected, measurement of individual LDH isoenzymes can be helpful. In combination with other laboratory values such as troponin (cardiac marker), AST and ALT (liver markers), or a complete blood count, the cause of an LDH elevation can often be narrowed down.
LDH as a Monitoring and Therapy Marker
In oncology, LDH is frequently used to monitor the course of cancer. Declining LDH levels may indicate a response to treatment, while rising levels can suggest disease progression or treatment failure. LDH also plays an important role in assessing the severity of certain conditions, such as pneumonia or COVID-19.
References
- Lothar Thomas: Labor und Diagnose. 8th edition. TH-Books, Frankfurt/Main, 2012.
- Kasper DL et al.: Harrison's Principles of Internal Medicine. 21st edition. McGraw-Hill Education, 2022.
- World Health Organization (WHO): Laboratory Diagnostics and Biomarkers in Clinical Practice. Available at: www.who.int
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