What Does LDH Mean on a Blood Test?

What it means

LDH stands for lactate dehydrogenase. It is an enzyme that helps cells turn sugar into energy. Almost every tissue has it, including the heart, liver, muscles, kidneys, lungs and red blood cells. When cells are damaged or break down, LDH spills into the blood.

Because it comes from so many places, LDH is a general marker of tissue damage rather than a test for one organ. Doctors use it to follow conditions where cells are breaking down, such as the destruction of red cells (hemolysis), some cancers, and some lung and muscle problems. It is often checked more than once to see whether the number is rising or falling.

A common cause of a falsely high LDH is a hemolyzed sample, where red cells burst in the tube after the blood was drawn. The lab may add a comment when this happens. LDH is also not the same as lactate (lactic acid), which is a separate test.

Where you may see it

• Hospital blood panels, especially during an admission
• Hematology and cancer clinic follow-up results
• Lab comments such as "Hemolyzed: LDH may be falsely raised"