Lactate Dehydrogenase Isoenzymes
Does this test have other names?
LDH, lactic dehydrogenase
What is this test?
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 healthcare
providers which tissue may be damaged or injured.
Why do I need this test?
You might have this test to see whether you have had a heart attack, blood disorder,
or damage to your liver or other tissues.
What other tests might I have along with this test?
Your healthcare provider might order other blood tests that can detect elevated enzyme
For liver enzymes:
Aspartate aminotransferase, or AST
Alanine aminotransferase, or ALT
For heart and skeletal muscle:
Your healthcare provider might also order a urine test for LDH.
What do my test results mean?
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 healthcare
Normal results for isoenzymes are listed below.
LDH-1: 17% to 27%
LDH-2: 27% to 37%
LDH-3: 18% to 25%
LDH-4: 3% to 8%
LDH-5: 0% to 5%
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. Healthcare providers refer to this as "flipped LDH" because normally
your LDH-2 is higher than your LDH-1.
When your LDH-5 is greater than your LDH-4 it could mean you have damage to your liver
or liver disease. This includes cirrhosis and hepatitis.
If you have two diseases that have caused more than one LDH isoenzyme to rise, one
disease could hide the other.
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your
Does this test pose any risks?
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.
What might affect my test results?
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 medicines can elevate your LDH.
Medicines that contain ascorbic acid (vitamin C) can decrease your LDH levels. Alcohol
also can affect your LDH levels.
How do I get ready for this test?
You don't need to prepare for this test. Be sure your healthcare provider 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.