What is lactate dehydrogenase?
Lactate dehydrogenase (LDH) is an enzyme required during the process of turning sugar into energy for your cells. LDH is present in many kinds of organs and tissues throughout the body, including the liver, heart, pancreas, kidneys, skeletal muscles, lymph tissue, and blood cells.
When illness or injury damages your cells, LDH may be released into the bloodstream, causing the level of LDH in your blood to rise. High levels of LDH in the blood point to acute or chronic cell damage, but additional tests are necessary to discover its cause. Abnormally low LDH levels only rarely occur and usually aren’t considered harmful.
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-1: heart and red blood cells
- LDH-2: heart and red blood cells
- LDH-3: lymph tissue, lungs, platelets, pancreas
- LDH-4: liver and skeletal muscle
- LDH-5: liver and skeletal muscle
Because LDH is present in so many types of cells, high levels of LDH may indicate a number of conditions. Elevated levels of LDH can include:
- blood flow deficiency
- cerebrovascular accident, also known as a stroke
- certain cancers
- heart attack
- hemolytic anemia
- infectious mononucleosis
- liver disease, such as hepatitis
- muscle injury
- muscular dystrophy
- pancreatitis
- tissue death
- use of alcohol or certain drugs
- sepsis and septic shock
Doctors normally measure LDH levels in the blood. In some conditions, doctors may measure LDH levels in the urine or cerebrospinal fluid (CSF).
In adults, a technician usually draws blood from a vein at the inner elbow or the back of the hand. The technician will clean the test area with an antiseptic and wrap an elastic band around the upper arm to make the vein swell.
Then, they will gently insert a needle, through which blood flows into an attached tube. When the tube is full, the technician removes the elastic band and then the needle. A bandage protects the puncture site.
In infants, a sharp tool called a lancet may be necessary to take a blood sample. The blood collects in a small tube. The technician may place a bandage over the cut. Normally, there is some pain when the lancet pierces the skin, and some throbbing afterward.
Certain medications and drugs may interfere with an accurate LDH test. Large amounts of vitamin C (ascorbic acid) may lower LDH levels. Alcohol, anesthetics, aspirin, narcotics, and procainamide may raise LDH levels. Strenuous exercise may also raise LDH levels. Ask your doctor about any medications you should avoid before the test.
Typical ranges for LDH levels
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 LDH levels
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.
Low LDH levels
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).
Measuring LDH can be a useful tool for doctors when evaluating and treating certain medical conditions. Normal ranges vary with age. As scientists continue to learn more about the role of LDH in the body, the usefulness of monitoring LDH levels in certain diseases and conditions will likely increase.