An LDH (lactate dehydrogenase) test is a common blood examination used to assess potential tissue damage within the body. This test measures the levels of the LDH enzyme, which is present in various cells and tissues. When cells are injured or diseased, they can release this enzyme into the bloodstream, leading to elevated levels that healthcare providers can measure. The test serves as a general indicator that tissue health may be compromised.
Understanding Lactate Dehydrogenase
Lactate dehydrogenase (LDH) is an enzyme found in nearly all living cells, playing a central role in the body’s energy production. It facilitates the reversible conversion of lactate to pyruvate, a process crucial for cells to generate energy, particularly when oxygen levels are limited. This function is especially important in muscle cells during intense activity.
LDH is distributed widely throughout the body, with notable concentrations in tissues such as muscles, the liver, kidneys, red blood cells, and the heart. The enzyme exists in five distinct forms, known as isoenzymes (LDH-1 through LDH-5), each with a slightly different structure and predominant location. For instance, LDH-1 is primarily found in the heart and red blood cells, while LDH-5 is more concentrated in the liver and skeletal muscles.
What Constitutes a Normal LDH Level?
Normal LDH levels can vary significantly depending on the laboratory conducting the test, as different methods and equipment are used. Generally, for adults, typical reference ranges fall between 140 to 280 units per liter (U/L).
For children, normal LDH levels are typically higher than in adults.
It is important to compare any test result against the specific reference range provided by the performing laboratory. A result within the established normal range usually suggests that general tissue health is within expected parameters at the time of testing. However, a normal LDH level does not always rule out disease, as some conditions may not immediately cause an elevation.
Interpreting Elevated LDH Levels
Elevated LDH levels signal tissue damage or disease. When cells are damaged or destroyed, they release their contents, including LDH, into the bloodstream. This makes LDH a general marker for cellular breakdown.
Numerous conditions can lead to an increase in LDH. These include significant events such as heart attacks, which damage cardiac muscle cells, and various liver diseases like hepatitis or cirrhosis. Kidney diseases and muscle injuries, including muscular dystrophy, can also cause LDH to rise.
Certain blood disorders, such as hemolytic anemia where red blood cells are prematurely destroyed, or megaloblastic anemia, commonly result in elevated LDH. Infections like meningitis, encephalitis, mononucleosis, and sepsis can also trigger increases due to widespread tissue inflammation or damage. Furthermore, some cancers, including lymphomas, leukemias, and metastatic cancers, are associated with higher LDH levels.
Other potential causes of elevated LDH include bone fractures, pancreatitis, stroke, and pulmonary embolism. In pregnant individuals, high LDH levels can be associated with conditions like preeclampsia. It is important to note that LDH elevation is not specific to a single organ or condition, meaning further diagnostic tests are typically necessary to pinpoint the exact cause of the damage.
Understanding Low LDH Levels and Influencing Factors
Low LDH levels are less frequently observed and are generally considered less clinically significant than elevated levels. In rare instances, a low LDH reading might indicate a genetic condition, such as lactate dehydrogenase A or B deficiency. These rare disorders can affect how the body processes glucose for energy, with some individuals experiencing symptoms like fatigue or muscle pain during physical activity.
Several factors can influence LDH test results without necessarily indicating an underlying disease. One common non-disease related cause of falsely low LDH is high doses of vitamin C. Certain medications, including aspirin, anesthetics, narcotics, and procainamide, can also affect LDH levels, sometimes causing them to appear higher.
Physical activity can also impact LDH; strenuous exercise can temporarily increase LDH levels due to normal muscle exertion and repair processes. Additionally, improper handling of a blood sample can lead to inaccurate results. If red blood cells are damaged during collection or transport, they release their internal LDH, artificially inflating measured levels.