A high level of Lactate Dehydrogenase (LDH) in a child’s lab results can be concerning. LDH is an enzyme present in nearly all cells, playing a fundamental role in energy production by converting lactate to pyruvate. Elevated levels in the bloodstream signal that cells have been damaged or are undergoing rapid turnover, causing their internal contents to spill out. The result confirms tissue damage has occurred somewhere in the body, but LDH is a non-specific marker that does not specify the location or the exact cause. Understanding the reasons for its elevation is the first step in addressing the result with context.
What Lactate Dehydrogenase Is and What It Measures
LDH is widely distributed, with the highest concentrations found in the heart, liver, skeletal muscles, kidneys, and red blood cells. Because it exists in so many tissue types, an elevated total LDH level acts as a general alarm rather than a specific diagnosis. When a cell is injured or dies, the LDH contained within its cytoplasm is released into the circulation, indicating tissue damage.
To help narrow down the source, LDH is divided into five distinct forms called isoenzymes, labeled LDH-1 through LDH-5. These isoenzymes are concentrated differently in various organs; for example, LDH-1 is associated with the heart and red blood cells, while LDH-5 is concentrated in the liver and skeletal muscle. Doctors may use isoenzyme testing as one tool to gain an initial clue about the organ system involved.
Common Causes of High LDH in Children
In the pediatric population, a high LDH result is often temporary and attributed to benign, non-pathological causes. A frequent reason for mild elevation is strenuous physical activity shortly before a blood draw, as the enzyme leaks from muscle cells following exertion. Even minor bumps or muscle aches from active play can cause a transient rise in the enzyme level.
A common technical cause of a falsely elevated result is in vitro hemolysis, which is the breakdown of red blood cells within the blood sample tube itself. Since red blood cells contain a very high concentration of LDH, improper handling or vigorous mixing of the sample can artificially inflate the measured level. Furthermore, children frequently experience minor viral infections, such as the common cold, which cause widespread cell turnover and inflammation that can lead to mild LDH increases. Infectious mononucleosis is also known to cause significant but temporary elevations.
When High LDH Indicates a Serious Condition
While often benign, a high LDH level can mark significant underlying medical conditions, though these are less common. One major concern is hemolytic anemia, a condition causing excessive red blood cell destruction, where the rapid breakdown of these LDH-rich cells floods the bloodstream with the enzyme. Severe, long-term conditions affecting major organs, such as progressive muscular dystrophy or significant liver disease like hepatitis, can also cause persistently elevated LDH levels due to ongoing tissue damage.
LDH is also used as a tumor marker because certain types of rapidly growing cancers, including lymphomas and leukemias, cause substantial elevations. Malignant cells have a high metabolic rate and turnover quickly, releasing large amounts of LDH into the circulation. For these serious conditions, the LDH level is considered alongside the child’s physical symptoms, medical history, and the results of other specific blood tests.
Diagnostic Follow-Up and Interpretation
The initial high LDH result prompts the healthcare provider to order additional, more specific tests to determine the source of the enzyme release.
Initial Testing
A complete blood count (CBC) is performed to assess for anemia or abnormal white blood cell counts, which may indicate blood disorders or malignancy. Organ function is evaluated using a comprehensive metabolic panel, including liver enzymes (AST and ALT) and kidney function tests.
Further Investigation
The physician may request a repeat LDH test to determine if the level was a temporary spike or a sustained elevation. If the cause remains unclear, a doctor may proceed with imaging studies or LDH isoenzyme testing to localize the source of the damage. The LDH level itself is not treated; rather, the underlying condition responsible for the cellular damage is the target of any necessary medical intervention. The final interpretation of a high LDH result is made by correlating the lab value with the child’s overall health, physical examination findings, and the results of all other diagnostic procedures.