Lactate dehydrogenase (LDH) is an enzyme present in nearly all cells throughout the body, playing a fundamental role in energy production. This enzyme helps convert glucose into usable energy, particularly when oxygen levels are low. Under normal circumstances, LDH levels in the bloodstream are low. However, when cells are damaged or diseased, they release LDH into the bloodstream, making it a general indicator of tissue injury. Measuring LDH levels through a blood test can therefore offer insights into potential underlying health issues.
What LDH Levels Mean
A “normal” LDH level typically falls within a specific range, though these ranges can vary slightly between different laboratories. For adults, general reference ranges are often cited between 140 to 280 units per liter (U/L). Children generally have higher normal LDH levels than adults. An elevated or concerning LDH level is anything above the established normal range for a given laboratory.
LDH exists in various forms, known as isoenzymes, which are slightly different versions of the enzyme found in specific tissues. There are five main LDH isoenzymes (LDH-1 through LDH-5), each predominantly located in different parts of the body. For instance, LDH-1 is primarily found in the heart and red blood cells, while LDH-5 is largely present in the liver and skeletal muscles. Analyzing the levels of these individual isoenzymes can help pinpoint the specific tissue or organ experiencing damage.
Conditions Leading to High LDH
Elevated LDH levels often signal cellular damage resulting from various medical conditions, as damaged cells release their internal LDH into the bloodstream.
Tissue Damage and Injury
Tissue damage and injury are common causes of high LDH. Conditions such as a heart attack, stroke, muscle injury, or bone fractures can lead to elevated levels. For example, a significant increase in LDH-1 can indicate a heart attack, while increased LDH-5 may point to muscular dystrophy or liver damage. Kidney and liver diseases, including hepatitis, also frequently cause elevated LDH due to damage to these organs.
Blood Disorders
Blood disorders, particularly those involving the destruction of red blood cells, can significantly raise LDH levels. Hemolytic anemia, where red blood cells are prematurely destroyed, and megaloblastic anemia, caused by deficiencies in folic acid or vitamin B12, are examples where LDH levels can be substantially elevated. Leukemia and lymphoma can also result in increased LDH.
Infections
Infections are another category of conditions that can lead to high LDH. Severe infections, sepsis, mononucleosis, and certain types of meningitis or encephalitis can cause elevated LDH levels due to the cellular damage induced by pathogens or the body’s immune response. LDH levels often correlate with the severity of the infection.
Inflammatory Conditions
Inflammatory conditions, such as pancreatitis or severe inflammatory responses, can also cause LDH to rise. This occurs as inflammation often involves cellular damage and tissue destruction. Autoimmune diseases like systemic lupus erythematosus (SLE) or rheumatoid arthritis may also show elevated LDH levels during active disease phases, reflecting ongoing inflammation and tissue damage.
Cancers
Cancers frequently cause elevated LDH levels, as rapidly growing cancer cells release LDH when they die or are damaged. LDH can be elevated in various types of cancer, including testicular cancer, melanoma, non-Hodgkin lymphoma, and leukemia. In malignancy, elevated LDH is often associated with increased tumor burden, higher cell turnover, and can indicate a more aggressive disease with a poorer outlook.
Why LDH Levels Might Be Low
Lower-than-normal LDH levels are uncommon and generally not considered a health concern.
One potential reason for low LDH can be a rare genetic condition known as lactate dehydrogenase deficiency. This condition affects how the body processes sugar for energy in cells, primarily muscle cells. Depending on the specific genetic mutation, it can impact the LDH-A or LDH-B subunits of the enzyme. While LDH-A deficiency can lead to symptoms like muscle pain and exercise intolerance, LDH-B deficiency often presents with no symptoms and is typically discovered incidentally during routine blood tests. Additionally, very high doses of ascorbic acid (Vitamin C) have been noted to potentially cause falsely low LDH results.
The Importance of Medical Consultation
An LDH test is not a standalone diagnostic tool, and its results must always be interpreted by a healthcare professional. An abnormal LDH level indicates that tissue damage or disease may be present, but it does not specify the exact cause or location of the damage.
Healthcare providers will consider LDH levels in conjunction with a person’s symptoms, complete medical history, physical examination findings, and the results of other diagnostic tests. This comprehensive approach allows for an accurate diagnosis and the determination of the underlying cause of any abnormal LDH levels. Only a qualified doctor can accurately interpret these results and recommend the appropriate course of action or further investigation.