Lactate dehydrogenase (LDH) is an enzyme present in most body tissues. Normal LDH levels for adults are usually 140–280 units per liter (U/L) in the blood.

LDH is involved in cellular respiration, which is the process that converts energy from food into energy for cells.

Although LDH is abundant in cells, it does not typically circulate in the blood, so levels on LDH blood tests are usually low. However, if tissues become damaged by injury or disease, they release LDH into the bloodstream.

Conditions that can increase blood LDH include:

Doctors can use the LDH test to help them diagnose these conditions.

This article will discuss the LDH test, its uses, and what the results may mean.

A gloved hand holding the results of an LDH test. The results sit on a table next to a rack of phials.Share on Pinterest
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Lactate dehydrogenase (LDH) is an enzyme that exists in almost all body tissues, including the:

  • muscles
  • liver
  • heart
  • pancreas
  • kidneys
  • brain
  • blood cells

LDH helps convert a type of sugar known as lactate into pyruvate, which cells then use for energy.

If illness or injury damages cells, they release LDH into the bloodstream. As a result, measuring LDH levels in the blood can give doctors information about how much cell damage has occurred.

There are various forms of LDH that exist in different tissues. Doctors call them isoenzymes. They include:

  • LDH1 in the heart
  • LDH2 in the reticuloendothelial system (liver, spleen, lungs) and red blood cells
  • LDH3 in the lungs
  • LDH4 in the kidneys
  • LDH5 in the liver and skeletal muscle

Doctors use LDH tests to determine whether there is tissue damage inside the body they cannot see externally. They may also use LDH tests to monitor conditions that can damage tissues, such as:

LDH testing can also help doctors determine whether chemotherapy is working during cancer treatment.

For adults, normal LDH levels in the blood are usually 140–280 units per liter (U/L). Doctors use a person’s symptoms to help interpret the data.

Infants and young children usually have significantly higher normal levels of LDH. For example, in newborns, it is 135–750 U/L, and in children up to 12 months, it is 180–435 U/L.

Doctors can measure LDH via a blood test. Taking the sample is usually straightforward and only takes a few minutes.

First, a healthcare professional will draw up a person’s sleeve on their least dominant arm. They will find a vein on the inside of the elbow and clean the skin with an antiseptic. Next, they will insert a small needle into the vein. This may feel like a small, sharp scratch.

Once the needle is secure, the healthcare professional will draw out some blood into a tube. After taking enough blood, they will remove the needle and put a cotton ball on the puncture site to help stop any bleeding.

Finally, the healthcare professional will label and send the blood sample to a laboratory for testing.

Sometimes, doctors can also measure LDH by taking samples of other bodily fluids, such as from the spinal cord or lungs.

The LDH test is a low risk procedure. A person may feel a small pinch as the needle enters the vein. Afterward, there may be some bruising and soreness around the puncture site.

Some people may become dizzy or feel faint during the procedure. If this happens, a person can put their head between their knees or lie down on their side with their feet up.

When the laboratory returns the results, they will either be within the standard reference range or above or below it.

High LDH levels

LDH is present in many cells, so high levels may indicate various conditions, including:

  • hemolytic anemia
  • infections, such as COVID-19 or meningitis
  • muscle injury
  • stroke
  • some cancers
  • heart attack
  • liver disease
  • muscular dystrophy
  • pancreatitis

Because it can indicate so many conditions, doctors will combine an LDH test with other tests to make a diagnosis.

Low LDH levels

Unusually low LDH levels are very rare. Often, doctors do not consider it harmful. However, unusually low LDH levels can indicate a genetic condition known as LDH deficiency. People can inherit this condition from a parent. It interferes with how cells use energy.

There are two types of LDH deficiency. LDH-A deficiency causes fatigue, muscle pain, and exercise intolerance. It may also cause the breakdown of muscle tissue, which is known as rhabdomyolysis. This releases the protein myoglobin, which can damage the kidneys.

A person with LDH-B deficiency may have no symptoms.

Raised LDH levels during pregnancy can indicate preeclampsia. This is a serious complication that causes high blood pressure, raising the risk of complications for the parent and fetus, such as:

  • kidney injury
  • liver damage
  • problems with the placenta
  • pulmonary edema
  • hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome
  • seizure
  • death of the parent or baby

Key signs of preeclampsia are high blood pressure, protein in the urine, and high LDH. If a pregnant person has preeclampsia with severe features, their LDH levels could be as high as 400 U/L, which is 1.6 times the normal level.

Preeclampsia resolves after a person gives birth. Until then, doctors monitor the condition and advise people to rest and manage their blood pressure.

If a person is near their due date, doctors may suggest inducing labor early. In some cases, doctors may use medications to lower the risk of complications.

The LDH test is a blood test that looks for high levels of the enzyme lactate dehydrogenase. Elevated levels may indicate various conditions, including stroke, some cancers, heart attack, and infections.

High LDH levels during pregnancy can indicate preeclampsia, which causes high blood pressure. Low LDH levels are very rare and usually not harmful, but they may indicate LDH deficiency.