LDH (lactate dehydrogenase)
Enzyme found in almost all body tissues that enters the blood in larger amounts when tissue is damaged
Also known as
Definition
Lactate dehydrogenase (LDH) is an enzyme that helps cells make energy. It is found in almost all tissues, with especially large amounts in muscles, liver, kidneys and red blood cells. When such tissues are damaged, more LDH enters the blood. The value is therefore a general sign of tissue damage, but on its own it does not show where the damage is or what causes it. That is why LDH is usually measured together with other values.
| Parameter | Value |
|---|---|
| Unit | U/L (units per liter, also IU/L) |
| Reference Range | Typical for adults: 125–220 U/L (normal range according to MedlinePlus). Labs differ and some use other measurement methods; the reference range on your own report is what counts. Discuss any deviation with your doctor. |
Agree on your personal target range with your doctor.
Conversion to the SI unit katal (our own calculation): 1 U/L equals 1/60 µkat/L, or about 0.0167 µkat/L. 125–220 U/L is therefore about 2.08–3.67 µkat/L.
↓ What a low value means
A low LDH level is rare and is usually not considered a health problem. It can be linked to taking large amounts of vitamin C or vitamin E. Rarely, an inherited disorder called lactate dehydrogenase deficiency can be behind it. Discuss the result with your doctor.
↑ What a high value means
A high LDH level can be linked to tissue damage from disease, infection or injury. Possible areas include diseases of the blood (such as hemolytic anemia, in which red blood cells break down early), the liver, lungs, kidneys, heart, pancreas or muscles. A high value does not always mean a condition that needs treatment: intense physical exertion, certain medicines such as aspirin, or red blood cells that broke open while the sample was collected or processed can also raise it. An LDH isoenzyme test can help narrow down which tissue may be involved. Discuss the result with your doctor.
When to test
LDH is measured when symptoms or other findings suggest tissue damage, and to follow conditions that affect the value, such as anemia, liver or muscle diseases or certain cancers. No special preparation is needed for the blood draw.
Frequently asked questions
Does a high LDH level show which organ is affected? +
No. LDH is found in almost all tissues, so a high value alone shows neither where tissue damage is nor what causes it. That is why LDH is usually combined with other values. An LDH isoenzyme test measures five different forms of the enzyme and can help narrow down the source.
Can intense training affect the LDH level? +
Yes. Intense physical exertion can raise the LDH level without a condition that needs treatment. When you discuss your report, tell your doctor if you trained intensely before the blood draw.
What does it mean if the sample is hemolyzed? +
Hemolysis means that red blood cells in the sample broke open, for example during collection or processing. Their LDH then enters the sample, and the measured value can come out higher without this having to reflect tissue damage in the body.
Do I need to fast for an LDH test? +
No, no special preparation is needed for the blood test. The blood draw from a vein in your arm usually takes less than five minutes. In certain cases LDH is also measured in other body fluids, such as cerebrospinal fluid; your doctor will then explain the procedure.
LDH (lactate dehydrogenase)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.