Lactate dehydrogenase (LDH) is an enzyme found inside almost every cell of the human body that helps convert sugar into energy. When cells are damaged or destroyed by illness or injury, they release their contents, including LDH, into the bloodstream. This article will provide general information about what an elevated LDH level might signify.
Contextualizing an LDH Level of 400
LDH is present in tissues throughout the body, including the heart, liver, muscles, kidneys, lungs, and red blood cells. At the cellular level, it helps produce energy, particularly when oxygen is limited. The reference range for LDH in the blood can vary between laboratories, but for adults, it is often between 122 and 225 units per liter (U/L). Some labs may cite a slightly different range, such as 140 to 280 U/L.
A result of 400 U/L is considered elevated. An elevated LDH level is a non-specific marker of tissue damage. This means that while the result indicates cellular injury has occurred, it does not, by itself, identify the location or the cause of the damage. Therefore, healthcare providers use it as one piece of a larger diagnostic puzzle.
Potential Causes of Elevated LDH
A wide array of conditions can cause cells to break down and release LDH, leading to a higher-than-normal level in the bloodstream. The interpretation of this finding depends on an individual’s overall health, symptoms, and the results of other medical tests. Some potential causes include:
- Intense physical activity can lead to a temporary increase in LDH levels due to the strenuous work of muscle cells.
- Significant muscle and tissue injuries, such as those from trauma, bone fractures, or rhabdomyolysis where muscle tissue breaks down rapidly.
- Conditions affecting the heart and lungs, such as a heart attack which damages heart muscle, or a pulmonary embolism which damages lung tissue.
- Diseases of the liver and kidneys, as the liver contains high concentrations of this enzyme. Conditions like hepatitis or cirrhosis will cause an increase.
- Blood disorders characterized by the destruction of blood cells, which releases a significant amount of LDH, such as in hemolytic anemia.
- Some cancers, particularly blood cancers like lymphoma and leukemia, can lead to very high LDH levels and the test is used to monitor the disease.
- Severe infections like meningitis, mononucleosis, or widespread infection (sepsis) can cause generalized tissue damage.
The Role of LDH Isoenzymes
The general LDH test measures the total amount of the enzyme but doesn’t differentiate between its five forms, called isoenzymes. These are numbered LDH-1 through LDH-5, and each is concentrated in different tissues, which can help narrow down the source of cell damage.
The distribution of these isoenzymes is specific. LDH-1 and LDH-2 are found in the highest concentrations in the heart and red blood cells. LDH-3 is most concentrated in the lungs and spleen, while LDH-4 and LDH-5 are predominantly located in the liver and skeletal muscles.
If a total LDH level is high, a physician might order an LDH isoenzyme test. By measuring the relative amounts of each type, the pattern can point toward a specific organ. For example, a result showing LDH-1 levels higher than LDH-2 could suggest heart muscle injury, while high LDH-5 would point toward the liver.
The Diagnostic Follow-Up Process
An elevated LDH level is not a diagnosis but a signal that prompts further investigation. A healthcare provider will integrate this clue with other information, including a patient’s medical history, current symptoms, and a complete physical examination.
The provider will also analyze the results of other blood tests that are often ordered at the same time. These include a complete blood count (which examines red and white blood cells) and a comprehensive metabolic panel (which includes tests for liver and kidney function).
Based on this initial assessment, more specific tests may be ordered. This could include the LDH isoenzyme test to help pinpoint the organ system involved or imaging studies such as a chest X-ray, an ultrasound, or a CT scan to visualize internal organs.