LDH Blood Test: Normal Range and High Levels

What is LDH?

LDH, short for lactate dehydrogenase, is an enzyme found throughout your body. Your muscles, liver, kidneys, and red blood cells contain especially large amounts.

A small amount normally circulates in your blood. When cells suffer damage or break down, they release more LDH into the bloodstream. 

Your report may call this measurement LD, lactate dehydrogenase, or lactic acid dehydrogenase. These names refer to the same enzyme.

When do doctors recommend an LDH test?

Doctors may request an LDH test to:

• Investigate suspected tissue damage or unexplained anemia.
• Assess conditions that affect the liver, muscles, kidneys, or lungs.
• Evaluate certain severe infections.
• Monitor some cancers or their response to treatment.

The reason for testing matters. The same result can have different meanings in someone with a recent muscle injury and someone who already receives cancer treatment.

How does an LDH blood test work?

A healthcare professional takes a blood sample from a vein in your arm. The laboratory measures LDH enzyme activity and reports the result in units per liter, usually U/L or IU/L.

You usually do not need to fast for LDH testing alone. Follow your laboratory’s instructions if you have other blood tests at the same appointment.

Tell your doctor about medicines, supplements, and recent intense exercise, since these can affect results. Do not stop prescribed treatment without medical advice.

What is the LDH normal range?

UCSF Health lists an LDH reference range of 125-220 IU/L. However, laboratories use different methods and reference intervals, so your own report’s range takes priority.

For example, a result of 230 U/L would fall above a laboratory’s upper limit of 220 U/L, but within a range that ends at 250 U/L.

Children can have higher normal LDH levels than adults. Use the laboratory’s age-specific range rather than an adult range when reviewing a child’s result.

A result outside the reference range does not establish a diagnosis. Your doctor also considers how far it falls outside that range and whether it changes on repeat testing.

What do high LDH levels mean?

High LDH levels can indicate tissue damage or increased cell breakdown. The result alone cannot identify the affected organ or confirm a diagnosis.

Possible causes include:

• Hemolytic anemia: Red blood cells break down faster than the body can replace them.
• Liver disease: Conditions such as hepatitis can damage liver cells and release LDH.
• Muscle injury: Muscle damage or intense exercise can raise levels.
• Infections: Some infections, including infectious mononucleosis, can increase LDH.
• Reduced blood supply: A lack of oxygen can damage tissues.
• Certain cancers: Conditions such as lymphoma or leukemia may raise LDH. However, high LDH alone does not mean you have cancer.

Red blood cells can also break during sample collection or handling, causing a falsely high result. Your laboratory may describe the sample as hemolyzed, and your doctor may request another blood draw.

Recommendations

Treatment depends on the cause of the elevation. Your doctor may recommend these steps:

• Repeat the LDH test: A fresh sample can help confirm the result, especially if the laboratory reports hemolysis.
• Check for red blood cell breakdown: Tests may include CBC, haptoglobin, bilirubin, and reticulocyte count.
• Assess liver or muscle health: Your doctor may check ALT and AST for liver injury, or creatine kinase for muscle damage.
• Review possible influences: Tell your doctor about recent intense exercise, medicines, and supplements. Do not stop prescribed treatment without medical advice.
• Follow up on persistent elevations: Your doctor can compare results over time and investigate the underlying cause.

Which doctor should you see for abnormal LDH?

Start with the doctor who ordered the test or your primary care doctor. They can review the result and decide whether you need further evaluation.

A hematologist may assess suspected blood cell disorders. A liver specialist may evaluate liver-related abnormalities, while an oncologist interprets LDH in people with a suspected or confirmed cancer.

Seek urgent medical care for chest pain, sudden shortness of breath, fainting, or severe weakness. Symptoms determine urgency more reliably than an LDH number alone.