LD

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. LD is an enzyme that is found in almost all of the body's cells (as well as in bacteria) and is released from cells into the fluid portion of blood (serum or plasma) when cells are damaged or destroyed. Thus, the blood level of LD is a general indicator of tissue and cellular damage. The level of LD may also rise in other types of body fluids (e.g., cerebrospinal fluid, pleural fluid, etc.) in the presence of certain diseases.

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 megaoloblastic 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.

Blood test
An LD level may be ordered, along with other tests such as a comprehensive metabolic panel (CMP), when a health 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 levels may also occasionally be ordered when an individual has experienced muscle trauma or injury or when a person has signs and symptoms of hemolytic anemia.

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.

Blood test
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
• Sepsis
• Intestinal and lung (pulmonary) infarction
• Acute kidney disease
• Acute liver disease
• Acute muscle injury
• Pancreatitis
• Bone fractures
• Testicular cancer, lymphoma or other cancers

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).

Body fluids:

• 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 Tests (above).

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.

Historically, the LD test was used to help diagnose and monitor a heart attack, but the test for troponin has largely replaced LD in this role. LD is not specific for damage to the heart and is no longer recommended for evaluating people with suspected acute coronary syndrome (ACS).