Lactate dehydrogenase (LDH) is an enzyme that helps facilitate the process of turning sugar into energy for your cells to use. LDH is present in many kinds of organs and tissues throughout the body, including the liver, heart, pancreas, kidneys, skeletal muscles, brain, 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 indicate acute or chronic cell damage, but additional tests will be necessary to discover its cause. Abnormally low LDH levels occur only rarely and are not usually harmful.
There are five different forms of LDH, and they are distinguished by slight differences in their structure. Each form of the LDH enzyme is called an isoenzyme. 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 listed below:
- LDH-1: heart and red blood cells
- LDH-2: white blood cells
- LDH-3: lungs
- LDH-4: kidneys, placenta, and pancreas
- LDH-5: liver and skeletal muscle
LDH levels are normally measured using a blood draw. Occasionally, LDH levels may be measured using urine or cerebrospinal fluid.
In adults, blood is taken 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, the needle is gently inserted, and blood flows into a tube. When the tube is filled, the technician removes the elastic band and then the needle. A bandage may be placed over the puncture site.
In infants or young children, a sharp tool called a lancet may be used to take a blood sample. The blood is collected in a small tube or on a slide. A bandage may be placed over the cut.
Normally, there is some pain when the needle is inserted and some throbbing afterward.
Certain medications and drugs may interfere with an accurate LDH test. Vitamin C (ascorbic acid) may lower LDH levels. Alcohol, anesthetics, aspirin, fluorides, mithramycin, 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.
Because LDH is present in so many types of cells, high levels of LDH may indicate any one of a number of conditions. Elevated levels of LDH isoenzymes may indicate:
- blood flow deficiency
- cerebrovascular accident, such as a stroke
- certain cancers
- heart attack
- hemolytic anemia
- infectious mononucleosis
- liver disease, such as hepatitis
- low blood pressure
- muscle injury
- muscular dystrophy
- tissue death
- use of alcohol or certain drugs
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. When levels of all five LDH enzymes are high, it could indicate multiple organ failure.
Because LDH is found in so many tissues throughout the body, complete LDH levels alone will not be enough to determine the location and cause of your tissue damage. The levels of LDH isoenzymes will also need to be measured in order to reach a diagnosis. For example, high LDH-4 and LDH-5 may mean either liver damage or muscle damage, but liver disease cannot be confirmed without a full liver panel.
It’s normal for a person to have a higher level of LDH-2 than LDH-1. But after a heart attack, the level of LDH-1 rises and is usually higher than the level of LDH-2. This is called a flipped pattern. Total LDH level will rise within 24 to 72 hours after a heart attack and peak in two to four days. It will return to normal in about 10 to14 days. However, a test for troponin, a protein in myocardial cells, has proved to be a more accurate indicator of a heart attack.
A normal LDH-1/LDH-2 ratio is generally regarded as reliable evidence that a heart attack did not occur.
Once you have been diagnosed with a particular condition, your LDH levels may be measured regularly to track the progress of your treatment.
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, 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).