Lactate Dehydrogenase (LD)
Along with other tests, when a healthcare practitioner suspects that you have an acute or chronic condition that is causing tissue damage or cellular destruction; sometimes when you have been diagnosed with cancer; when you have symptoms of meningitis or have fluid accumulation in a specific part of your body
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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 test used?
A lactate dehydrogenase (LD or LDH) test is a non-specific test that may be used in the evaluation of a number of diseases and conditions.
An LD blood test may be used:
- As a general indicator of the existence and severity of acute or chronic tissue damage
- To detect and monitor progressive conditions such as anemia, including hemolytic anemia and megaloblastic anemia, or severe infections
- To help stage, determine prognosis, and/or monitor treatment (i.e., chemotherapy) of cancers, such as germ cell tumors (e.g., some types of testicular cancer and ovarian cancer), lymphoma, leukemia, melanoma, and neuroblastoma
An LD test is performed on body fluids for a few different reasons:
- To help evaluate cerebrospinal fluid and distinguish between bacterial or viral meningitis
- To evaluate other body fluids such as pleural, peritoneal or pericardial fluid and help determine whether the accumulation of fluid is due to injury and inflammation (exudate) or due to an imbalance of pressure within blood vessels and the amount of protein in the blood (transudate). This information is helpful in guiding treatment.
The article on Body Fluid Analysis lists some fluids other than blood that may be evaluated with an LD test.
When is it ordered?
An LD level may be ordered, along with other tests such as a comprehensive metabolic panel (CMP), when a healthcare practitioner suspects that a disease or condition is causing some degree of cellular or tissue damage. If LD is elevated, then more specific tests, such as ALT, AST or ALP, may help diagnose the condition and help determine which organs are involved. Once the acute or chronic problem is diagnosed, total LD levels may be ordered at regular intervals to monitor its progress and/or resolution.
LD testing may be ordered on a regular basis when an individual has been diagnosed with cancer.
Body fluid test
This test may be ordered, for example, when a person has signs and symptoms of meningitis or when someone has a buildup of fluid around the heart, lungs or in the abdomen.
What does the test result mean?
Elevated levels of LD usually indicate some type of tissue damage. LD levels typically will rise as the cellular destruction begins, peak after some time period, and then begin to fall. LD levels are elevated in a wide variety of conditions, reflecting its widespread tissue distribution.
An elevated level of LD may be seen with:
- Hemolytic anemia
- Pernicious anemia (megaloblastic anemia)
- Infections such as infectious mononucleosis (mono), meningitis, encephalitis, HIV
- Intestinal, myocardial (heart) and lung (pulmonary) infarction
- Acute kidney disease
- Acute liver disease
- Acute muscle injury
- Bone fractures
- Testicular cancer, lymphoma or other cancers
- Severe shock
- Lack of oxygen (hypoxia)
A high LD in the blood may indicate that treatment for cancer (e.g., chemotherapy) has not been successful. A high level is predictive of a poorer outlook for survival for those with cancer.
With some chronic and progressive conditions, moderately elevated LD blood levels may persist.
Low and normal levels of LD do not usually indicate a problem. Low levels are sometimes seen when someone ingests large amounts of ascorbic acid (vitamin C).
- Cerebrospinal fluid—a high LD indicates that meningitis is likely caused by bacteria, while a low or normal level indicates viral meningitis is more likely.
- A high LD indicates that pericardial fluid, peritoneal or pleural fluid is an exudate, while a low level indicates it is transudate. Transudates are usually caused by congestive heart failure or cirrhosis. Exudates have several possible causes and usually require additional testing to determine the cause. Read more about these tests by accessing the specific fluid article listed under Related Content (below).
Is there anything else I should know?
Many things can affect LD results that are not necessarily a cause for concern. For example:
- Strenuous exercise can cause temporary elevations in LD.
- Hemolysis of the blood specimen can cause falsely elevated results. This may happen if the specimen is handled roughly, stored in extreme temperatures, or if the sample was difficult to collect.
- If a person's platelet count is increased, serum LD can be artificially high and not reflective of the LD actually present in the circulation.
If the LD test is not specific, how can it be clinically useful?
The LD test can be useful because it can alert a healthcare practitioner that cellular injury is occurring. In a similar fashion, tests such as a C-reactive protein (CRP) warn that inflammation is occurring somewhere in the body.
Is there anything I can do to lower my LD?
What is an LD isoenzymes test?
A test for LD isoenzymes is rarely ordered and not widely available nowadays. In the past, the test was used to help diagnose and monitor heart attacks, but it has been replaced by the test for troponin. Though not a routine test, it may be used in differential diagnosis to help determine which organs are likely affected by tissue damage when the cause of an elevated total LD is not clear and cannot be determined using other specific tests.
LD exists in five different forms called isoenzymes. Although there is some overlap, each of the five LD isoenzymes tends to be concentrated in specific body tissues. In general, the isoenzyme locations tend to be:
- LD-1: heart, red cells, kidneys, germ cells
- LD-2: kidneys, red blood cells, lungs, heart (lesser amounts than LD-1)
- LD-3: lungs and other tissues
- LD-4: white blood cells, lymph nodes, muscles, liver (lesser amounts than LD-5)
- LD-5: liver, skeletal muscle
Determining which isoenzyme is elevated in the blood may give clues to where tissue damage is occurring in the body and/or which organs may be affected.