Also known as: LD, lactate dehydrogenase, lactic dehydrogenase, total LDH and LDH isoenzymes
Name: Lactate dehydrogenase, total and isoenzymes
Related tests: CK, CK-MB, Myoglobin, Troponin
Why is the test done?
To help identify the cause and location of tissue damage and to assess its progress; historically it was used to diagnose and monitor heart attacks, but troponin has largely replaced this test.
When is it done?
Together with other tests, when an acute or chronic condition that may cause tissue or cell destruction is suspected and when the problem needs to be identified and monitored.
What samples are required?
A blood sample from a vein in the arm.
What is being tested?
Lactate dehydrogenase (LDH, LD) is an enzyme found in all tissues, but only a very small amount is found in the blood. Normally this enzyme is contained inside cells. When cells are damaged or destroyed, LDH is released into the bloodstream, raising its concentration; it cannot be used to determine which type of cells are damaged. An increase in LDH can be detected either by measuring total LDH or its isoenzymes. The LDH level is the sum of five different isoenzymes (slightly different molecular versions of LDH). Total LDH reflects tissue damage but is not specific. On its own it cannot identify the cause or location of the damage.
Although there is some overlap, each of the five isoenzymes tends to be more concentrated in a specific tissue. For this reason measuring the individual isoenzymes can be used, together with other tests, to determine the disease or condition causing cell damage and the organ or tissue affected. The isoenzymes tend to be located as follows:
• LDH-1: heart, red blood cells, kidney cortex, germ cells
• LDH-2: heart, red blood cells, kidney cortex (less than LDH-1)
• LDH-3: lungs and other tissues
• LDH-4: white blood cells, lymph nodes, muscle, liver (less than LDH-5)
• LDH-5: liver, muscle
Together the isoenzymes make up total LDH, the largest share being LDH-2.
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
Today LDH is mainly used as an indicator of the presence and severity of acute or chronic tissue damage and is sometimes used as an indicator of the course of the disease. LDH isoenzymes are also used to determine which organ is damaged.
The use of LDH and its isoenzymes has now declined. Traditionally they were often used, together with other tests such as CK and CK-MB, to diagnose and monitor myocardial infarction. The characteristic rise, peak and fall of LDH and the increase of LDH-1 relative to LDH-2 (the “flipped ratio”) helped the doctor track the progression and treatment of a heart attack and distinguish it from other chest pain, such as angina. This use has been completely replaced by troponin, which is more sensitive and specific.
When is it requested?
Total LDH is requested, together with other tests, when cell or tissue damage is suspected. If total LDH is high, its isoenzymes may be requested or, more commonly, other tests such as ALT, AST or ALP to help diagnose certain conditions and identify the organ involved. Once the acute or chronic problem has been diagnosed, total LDH is requested at regular intervals to assess the progression or resolution of the disease.
LDH is occasionally requested to monitor damage caused by muscle injury or to detect haemolytic anaemia (anaemia caused by the breakdown of red blood cells, either because they are too fragile or for mechanical reasons such as artificial heart valves).
LDH and its isoenzymes may be requested together with CK and CK-MB when a patient has symptoms suggesting a heart attack, but this is increasingly rare. Today troponin, CK and CK-MB are preferred.
What does the test result mean?
High LDH levels and changes in the ratio between the isoenzymes usually indicate some type of tissue damage. LDH rises as cell destruction begins, peaks after a time and then starts to fall. After a heart attack, total LDH rises within 24-48 hours, peaks in 2-3 days and returns to normal within 10-14 days.
High LDH levels can occur with:
· Cerebrovascular accident (CVA, stroke)
· Medicines (anaesthetics, aspirin, narcotics, procainamide) and alcohol
· Haemolytic anaemia
· Pernicious anaemia (megaloblastic anaemia)
· Infectious mononucleosis
· Intestinal and pulmonary infarction
· Kidney disease
· Liver disease
· Muscular dystrophy
· Pancreatitis
· Some types of cancer
Some chronic or progressive conditions and some medicines can cause LDH levels to remain high.
Low or normal LDH levels do not indicate any particular problem. Low levels are sometimes seen in patients who take large amounts of ascorbic acid (vitamin C).
Is there anything else I should know?
Many things can affect LDH measurement. For example:
• Strenuous exercise can temporarily raise LDH;
• Haemolysis can cause false positives (“haemolysis” refers to the breakdown of red blood cells due to rough handling, extreme temperatures or a difficult blood draw);
• A high platelet count can give a falsely high LDH result.
1. Why are several LDH isoenzymes raised at the same time?
1. Why are several LDH isoenzymes raised at the same time?
Several LDH isoenzymes can rise at the same time if more than one organ is damaged, for example in a patient with pneumonia who has a heart attack. Another example is a patient with a progressive disease, such as cancer that has spread and gradually involves several organs. Although the different LDH isoenzymes are concentrated in specific organs, there is some overlap. A single cause can raise several isoenzymes. For example, vigorous exercise can raise LDH-1, LDH-2 and LDH-5.