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The Test Sample
What is being tested?
Lactate dehydrogenase (LD or LDH) is an enzyme involved in energy production that is found in almost all of the body's cells, with the highest levels found in the cells of the heart, liver, muscles, kidneys, lungs, and in blood cells; bacteria also produce LD. This test measures the level of LD in the blood or sometimes other body fluids.
Only a small amount of LD is usually detectable in the fluid portion of the blood (serum or plasma). LD is released from the cells into the serum when cells are damaged or destroyed. Thus, an LD blood level is a non-specific marker for the presence of tissue damage somewhere in the body. By itself, it cannot be used to identify the underlying cause or location of the cellular damage. However, it may be used, in conjunction with other blood tests, to help evaluate for and/or monitor conditions that lead to tissue damage, such as liver or blood diseases or cancer.
Sometimes when there is injury, inflammation, or infection within a specific area of the body, such as the brain, heart or lungs, fluid will accumulate or constituents of the fluid present will change. The level of LD present in the fluid may be useful in determining the cause. For example, LD is typically high in cerebrospinal fluid when an individual has bacterial meningitis. The LD test can also be used, along with other tests, to determine whether fluid accumulation, for example around the heart or lungs or in the abdominal cavity, is due to injury or inflammation (exudate) or due to an imbalance of fluid pressure inside blood vessels and the protein level in blood (transudate). The article on Body Fluid Analysis lists some fluids that may be evaluated using an LD test.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. Sometimes a special procedure may be performed to collect body fluid from the site affected (e.g., cerebrospinal fluid, pleural fluid, peritoneal fluid, etc.).
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.