LDH, lactic dehydrogenase
This is a blood test to measure the different LDH isoenzymes that may be in your blood. Enzymes are proteins that cause chemical reactions in your body and provide energy. LDH enzymes are found in many tissues in the body, including the heart, red blood cells, liver, kidneys, brain, lungs, and skeletal muscles.
LDH exists in five forms, or isoenzymes. Each isoenzyme has a slightly different structure and is found in different concentrations in different tissues. For example, LDH-1 is found mostly in red blood cells and heart muscle. LDH-3 is concentrated in the lungs, although it is also found in other tissues. When LDH isoenzymes spill into your blood, it indicates damaged or diseased tissue. The results may tell your doctors which tissue may be damaged or injured.
You might have this test to see whether you have had a heart attack, blood disorder, or damage to your liver or other tissues.
Your doctor might order other blood tests that can detect elevated enzyme levels.
For liver enzymes:
Aspartate aminotransferase, or AST
Alanine aminotransferase, or ALT
For heart and skeletal muscle:
Creatine phosphokinase, or CPK
Your doctor might also order a urine test for LDH.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
Normal results for isoenzymes are listed below.
LDH-1: 17 to 27 percent
LDH-2: 27 to 37 percent
LDH-3: 18 to 25 percent
LDH-4: 3 to 8 percent
LDH-5: 0 to 5 percent
Normal ratios are:
LDH-1 less than LDH-2
LDH-5 less than LDH-4
When your LDH-1 is greater than your LDH-2, it could mean that you had a heart attack in the past week. Doctors refer to this as "flipped LDH" because normally your LDH-2 is higher than your LDH-1.
An elevated LDH-5 could mean you have damage to your liver or liver disease.
If you have two diseases that have caused more than one LDH isoenzyme to rise, one disease could hide the other.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
If the blood sample is contaminated by broken red blood cells, a condition called hemolysis, your LDH will be elevated.
If you exercise strenuously before the sample is taken, you could have elevated LDH-1, LDH-2, and LDH-5.
Anesthetics, aspirin, narcotics, and certain other drugs can elevate your LDH. Drugs that contain ascorbic acid (vitamin C) can decrease your LDH levels. Alcohol also can affect your LDH levels.
You don't need to prepare for this test. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.