What Is a Lactate Dehydrogenase (LDH) Test?

Medically Reviewed by Jennifer Robinson, MD on September 20, 2023
3 min read

The lactate dehydrogenase (LDH) test looks for signs of damage to the body’s tissues.

LDH is an enzyme found in almost every cell of your body, including your blood, muscles, brain, kidneys, and pancreas.

The enzyme turns sugar into energy. The LDH test measures the amount of LDH in your blood or other body fluid.

When cells are damaged or destroyed, this enzyme is released into the fluid portion of blood. Doctors call this “serum” or “plasma.” LDH can also be released into other body fluid, including cerebrospinal fluid, which surrounds your brain and spinal cord.

Your doctor might order one for any number of reasons, such as:

  • To measure whether you have tissue damage and, if so, how much
  • To monitor severe infections or conditions like hemolytic or megaloblastic anemias, kidney disease, and liver disease
  • To help evaluate certain cancers or your cancer treatment

Depending on your condition, you may have LDH tests on a regular basis.

You might have an LDH test of body fluids to:

  • Find the cause of fluid buildup. It could be due to many things, like injury and inflammation. (It could also be brought on by an imbalance in the pressure within blood vessels and the amount of protein in your blood.)
  • Help determine if you have bacterial or viral meningitis.

You’ll have blood drawn through a needle inserted into a vein in your arm.

For LDH tests of the cerebrospinal fluid, you’ll need a lumbar puncture (also called a spinal tap). You’ll have a thin needle inserted into your lower back.

Before either test, you should let your doctor know about all the medicines, supplements, herbs, vitamins, and anything else you’re taking.

For the LDH blood test, they include:

  • Bleeding
  • Bruising
  • Infection
  • Soreness at the site where blood was taken

If you have a lumbar puncture, you might have some of these side effects:

Higher LDH levels in blood may be a sign of tissue damage or disease. Your blood LDH level can also let your doctor know if your disease is getting worse or whether your treatment is working.

Normal levels of LDH in the blood can vary depending on the lab, but usually range between 140 units per liter (U/L) to 280 U/L for adults and tend to be higher for children and teens.

In cerebrospinal fluid, normal levels are:

  • Less than 70 U/L for newborns
  • Less than 40 U/L for adults

Higher LDH levels in your cerebrospinal fluid may mean you have an infection or inflammation in your central nervous system. It could also mean you have a disease that affects your brain or spinal cord, like bacterial meningitis.

If your LDH levels are higher than normal, your doctor may order more tests to pinpoint where the damage is located. One of them looks at levels of your LDH isoenzymes. These are types of LDH. There are five different forms, ranging from LD-1 through LD-5.

Each of the five tends to be concentrated in specific body tissues. For example, LD-1 is usually located in the heart, red blood cells, kidneys, testes, and ovaries.

If your LDH levels are elevated, your doctor may also order ALT, AST, or ALP tests. These can help with a diagnosis or help determine which organs are involved.

Elevated blood LDH doesn’t always signal a problem. It might be the result of strenuous exercise. The level may also be high if your blood sample is handled roughly in the lab or not stored at the proper temperature. Sometimes, taking too much vitamin C can be to blame. Finally, your blood LDH might be high if your platelet count is higher than normal.

LDH levels that are in the normal or lower than normal range aren’t usually a problem.