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
There are five different forms of LDH that are called isoenzymes. They are distinguished by slight differences in their structure. The isoenzymes of LDH are LDH-1, LDH-2, LDH-3, LDH-4, and LDH-5.
Different LDH isoenzymes are found in different body tissues. The areas of highest concentration for each type of isoenzyme are:
LDH levels vary based on age and the individual laboratory. Infants and young children will have much higher normal LDH levels than older children or adults. LDH is often reported in units per liter (U/L). In general, normal ranges for LDH levels in the blood are as follows:
|Age||Normal LDH level|
|0 to 10 days||290–2000 U/L|
|10 days to 2 years||180–430 U/L|
|2 to 12 years||110–295 U/L|
|Older than 12 years||100–190 U/L|
High levels of LDH indicate some form of tissue damage. High levels of more than one isoenzyme may indicate more than one cause of tissue damage. For example, a patient with pneumonia could also have a heart attack. Extremely high levels of LDH could indicate severe disease or multiple organ failure.
Because LDH is in so many tissues throughout the body, LDH levels alone won’t be enough to determine the location and cause of tissue damage. A diagnosis will also require the use of other tests and images in addition to measuring the levels of LDH. For example, high LDH-4 and LDH-5 may mean either liver damage or muscle damage, but liver disease can’t be confirmed without a full liver panel.
Before the discovery of other blood markers for heart injury, LDH was used to monitor people with heart attacks. Now, troponin, a protein produced more specifically in heart cells, is often a more accurate indicator of a heart attack.
Once your doctor diagnoses your particular condition, they may measure your LDH levels regularly to track the progress of your treatment.
LDH levels are also often used during the treatment of certain cancers to predict outcomes and monitor the body’s response to medications.
LDH deficiency affects how the body breaks down sugar for use as energy in cells, particularly muscle cells. It’s very rare for a person to have low LDH levels.
Two types of genetic mutations cause low LDH levels. People with the first type will experience fatigue and muscle pain, especially during exercise. While those with the second type may have no symptoms at all. You may also have low LDH levels if you’ve consumed a large amount of ascorbic acid (vitamin C).