Lactate dehydrogenase (LDH) is an enzyme found in nearly all living cells, playing a significant role in energy production. It helps convert pyruvate to lactate and back, a process that regenerates molecules necessary for cells to continue producing energy, especially when oxygen levels are low. While a small amount of LDH is normally found in the blood due to natural cell turnover, its presence in higher concentrations signals that cells have been damaged or destroyed. Measuring LDH levels in the blood can therefore serve as a general indicator of tissue injury or disease.
Understanding LDH Reference Ranges
LDH reference ranges can vary considerably among different laboratories due to varying equipment and testing methods. A typical adult range is between 140 to 280 units per liter (U/L) or international units per liter (IU/L), though some sources indicate ranges from 105 to 333 IU/L. Age also influences these ranges, with infants and young children naturally having much higher LDH levels than adults; for example, newborns might range from 135 to 750 U/L. Strenuous exercise can also temporarily elevate LDH activity. Therefore, a single LDH number should always be interpreted by a healthcare professional within the context of an individual’s overall health, symptoms, and other diagnostic test results.
Common Causes of Elevated LDH
Elevated LDH levels stem from a wide array of conditions involving cell damage or destruction, reflecting the enzyme’s widespread presence in body tissues. Common causes include tissue damage from injuries or medical events like a heart attack, where damaged heart muscle releases LDH into the bloodstream. Muscle injuries from trauma, intense exercise, rhabdomyolysis, or muscular dystrophy also elevate LDH. Liver diseases, such as hepatitis or cirrhosis, and kidney diseases can also lead to increased LDH when their cells are injured.
Blood disorders frequently cause elevated LDH due to the destruction of blood cells. Hemolytic anemia, characterized by the premature rupture of red blood cells, is a notable cause, as are other anemias like pernicious anemia (B12 deficiency). Severe infections, including sepsis, meningitis, encephalitis, and HIV, can also lead to elevated LDH levels due to widespread inflammation and cellular destruction.
Certain types of cancer are also associated with elevated LDH, particularly rapidly growing tumors like lymphomas, leukemias, melanoma, and testicular cancer. In these cases, the increase in LDH can be linked to high cell turnover and tumor lysis. Additionally, conditions such as pancreatitis, lung diseases like pulmonary embolism or pneumonia, and even certain medications or alcohol abuse can contribute to increased LDH levels.
Interpreting the Clinical Significance of High LDH
An elevated LDH level serves as a general marker of cell damage or disease, but it is not specific to any single condition or location in the body. This means that while a high LDH result indicates an underlying health issue, it does not pinpoint the exact cause on its own. For instance, both a heart attack and a muscle injury can lead to increased LDH. The degree of LDH elevation can sometimes correlate with the severity or extent of the underlying condition or tissue damage.
Very high LDH levels might suggest more widespread or severe issues compared to only slightly elevated levels. For example, a significant increase in LDH-5, one of the LDH isoenzymes, can indicate hepatocellular injuries like hepatitis or cirrhosis. In the context of cancer, higher LDH levels often suggest more advanced disease and can be associated with a less favorable outlook. Therefore, “dangerous” in this context refers to the fact that an elevated LDH level signals a health problem that warrants thorough medical investigation and potential treatment, rather than being inherently harmful itself.
Next Steps After an Elevated LDH Result
If an LDH test result comes back elevated, the next appropriate step is to consult a healthcare professional for proper evaluation and diagnosis. Self-diagnosis or attempting to treat an underlying condition based solely on an LDH test is not advisable. The doctor will likely order additional, more specific tests to determine the exact cause of the elevation.
These further tests might include specific organ function tests, such as liver enzyme tests or cardiac enzyme tests, as well as blood counts or imaging studies like CT scans or MRIs. In some cases, an LDH isoenzyme test may be performed, which measures the five different forms of LDH to help identify the tissue of origin for the elevated levels. The timing and selection of these investigations will be guided by the individual’s symptoms, medical history, and physical examination findings.