Lactate Dehydrogenase (LDH) is an enzyme found inside the cells of almost every organ and tissue throughout the body. The LDH test is a routine blood analysis often used as a general indicator of tissue damage or injury, since the enzyme is released into the bloodstream when cells are destroyed. While a high LDH level is a common sign of cell death in organs like the heart, liver, or muscles, a finding of low LDH is far less common. This unusual result typically does not indicate a serious health problem and often requires a different interpretation than an elevated value.
The Biological Function of LDH
LDH plays a function in cellular energy production, particularly in the process known as glycolysis. The enzyme catalyzes the reversible reaction between pyruvate and lactate, acting as a metabolic bridge for cells. This conversion is especially important when oxygen is scarce, such as during intense exercise in muscle tissue.
When oxygen is limited, LDH regenerates the coenzyme NAD+ by converting pyruvate into lactate, allowing the cell to continue producing energy in an anaerobic state. The lactate produced in muscle cells can then be transported to the liver and converted back into glucose (the Cori cycle). LDH is found in high concentrations in tissues with high metabolic demands—like the skeletal muscles, liver, heart, and kidneys—and its release into the blood is a direct consequence of cell damage in these areas.
Specific Causes of Low LDH Test Results
One of the most frequent reasons for a low LDH result is a technical issue known as an in vitro or laboratory interference. High intake of Vitamin C, or ascorbic acid, is a common cause of this phenomenon. As a powerful reducing agent, high concentrations of Vitamin C in the blood can interfere with the chemical assays used by the laboratory to measure LDH activity. This interference results in a falsely lowered reading that does not reflect the true amount of enzyme in the patient’s body.
Another possible cause is the presence of certain medications designed to suppress LDH activity. Some chemotherapy and cancer treatments, such as specific LDH inhibitors, are developed to block the enzyme’s function in cancer cells, which often rely on high LDH activity for growth. While these drugs are intended to treat a specific disease, they can lead to measurably low LDH levels in the blood. Anabolic steroids are also known to reduce LDH concentration, sometimes by as much as 40 percent.
A rare biological cause is a genetic condition called Lactate Dehydrogenase deficiency (LDH-A or LDH-B deficiency). This inherited metabolic disorder impairs the body’s ability to process sugar for energy, particularly in muscle tissue. Depending on the specific type, symptoms can range from muscle pain and fatigue during strenuous exercise to being completely asymptomatic. Low overall enzyme production due to chronic liver disease, malnutrition, or low muscle mass can also contribute to a low reading.
Interpreting the Significance of Low LDH
Unlike high LDH, which signals acute tissue damage and requires immediate investigation, a low LDH level is rarely a cause for alarm. It is generally not considered a clinically significant finding and is often incidental, requiring only a simple re-test.
When a low level is detected, the first step is to investigate potential lab interference, specifically asking about high-dose Vitamin C supplementation. If the result remains low, a clinician may consider the rare possibility of a genetic LDH deficiency, especially if the patient reports symptoms like exercise intolerance. The finding of a low LDH value often points toward a technical issue or a benign, non-pathological variation.