Lactate dehydrogenase (LDH) is an enzyme that helps 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 point to acute or chronic cell damage, but additional tests are necessary to discover its cause. Abnormally low LDH levels occur only rarely and usually aren’t 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:
- 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
Because LDH is present in so many types of cells, high levels of LDH may indicate 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
Doctors normally measure LDH levels using a blood draw. Occasionally, doctors may measure LDH levels using urine or cerebrospinal fluid.
In adults, a technician 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 the needle, and blood flows into a tube. When the tube is full, the technician removes the elastic band and then the needle. A bandage protects the puncture site.
In infants or young children, a sharp tool called a lancet may be necessary to take a blood sample. The blood collects in a small tube or on a slide. The technician may place a bandage over the cut. Normally, there is some pain when the needle pierces the skin, 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.
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. High levels of all five LDH isoenzymes could indicate multiple organ failure.
Because LDH is in so many tissues throughout the body, complete LDH levels alone won’t be enough to determine the location and cause of your tissue damage. A diagnosis will also require measuring the levels of LDH isoenzymes. 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.
It’s normal for a person to have a higher level of LDH-2 than LDH-1. After a heart attack, however, 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 to 14 days. A test for troponin, a protein in myocardial cells, is a more accurate indicator of a heart attack.
A normal LDH-1/LDH-2 ratio is generally regarded as reliable evidence that you didn’t have a heart attack.
Once your doctor diagnoses your particular condition, they may measure your LDH levels regularly to track the progress of your treatment.
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, 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).