What is LDH or Lactate Dehydrogenase Serum Test?

The LDH serum test is a simple blood test used to measure the amount of lactate dehydrogenase in your bloodstream. Doctors often use it to detect signs of tissue damage or monitor conditions like liver disease, heart problems, or certain cancers.

LDH is an enzyme your body uses to convert sugar into energy. It normally stays inside your cells, but when there’s damage—due to illness, injury, or stress—it leaks into the blood. The test checks how much of this enzyme has entered your bloodstream, helping doctors understand if something’s affecting your organs.

There are five different forms of LDH, called isoenzymes, each linked to specific organs. A rise in a certain type of LDH can give clues about where damage may be happening—whether in your heart, liver, muscles, or elsewhere. That’s why LDH is often used as a broad marker of internal stress or disease.

Doctors may order an LDH test when they suspect that tissue damage has occurred or want to monitor a condition already diagnosed. This includes situations like:

• Possible heart attack
• Liver disorders, such as hepatitis or cirrhosis
• Blood disorders, including anemia or infections
• Muscle injuries or trauma
• Tracking treatment for cancer or HIV

The test is also used to monitor how well a treatment is working—particularly for conditions like lymphoma or lung disease—where changes in LDH levels can indicate improvement or progression.

Patients experiencing symptoms of tissue damage or disease, such as weakness, exhaustion, appetite loss, or unexplained weight loss, might be required to undergo an LDH test. The test could help diagnose or monitor ailments like liver, heart, and some types of cancer.

Doctors may also order an LDH test for patients who have suffered physical trauma or injury, as high levels of LDH can indicate cell damage or destruction.

In addition, patients undergoing certain treatments, such as chemotherapy or radiation therapy, might have regular LDH tests to gauge their body's reaction and track the medication's effectiveness.

The LDH test measures the total concentration of lactate dehydrogenase in your blood. Some labs may also test LDH isoenzymes to identify which part of the body may be affected.

Elevated LDH alone doesn’t confirm a diagnosis—but it signals that some type of cellular stress or damage is happening. Depending on your symptoms and medical history, your doctor may suggest further testing.

LDH levels are measured using a spectrophotometric method. Here’s what happens behind the scenes:

• In the lab, your blood sample is mixed with a special reagent.
• LDH in the sample helps convert a substance called lactate into pyruvate.
• This reaction produces NADH, which absorbs light.
• The machine then tracks how much light is absorbed, which directly correlates with how much LDH is present.

It’s a fast, reliable technique used across labs worldwide.

This test doesn’t usually require any major preparation. But here are a few tips:

• Fasting may be requested by some labs, especially if other tests are being done at the same time.
• Let your doctor know about any medications you’re taking. Some drugs—including anesthetics, aspirin, and certain antibiotics—can influence LDH levels.
• Avoid strenuous exercise the day before, as it might elevate your LDH reading.
• Stay hydrated, and follow any specific instructions given by your doctor or lab.

The test process is straightforward and takes just a few minutes:

• A technician will clean a small area of your arm.
• A needle is inserted into a vein to draw a blood sample.
• After the sample is collected, a bandage is applied to the site.

You may feel a slight sting when the needle goes in, but it’s brief. There’s no downtime needed—you can resume your normal activities right away.

The normal LDH range in adults is generally 140 to 280 units per litre (U/L).

However, this can vary slightly depending on the lab’s reference range and the testing method used. Your doctor will interpret the result in the context of your overall health, symptoms, and any ongoing treatment.

High LDH Levels may indicate Heart problems, like a recent heart attack, Liver disease, including hepatitis or cirrhosis, Lung infections or chronic lung damage, Anemia or other blood-related conditions, Muscle injuries or Certain cancers, especially blood-related ones.

Low LDH Levels are rare and usually not a concern. Occasionally, it may result from genetic enzyme deficiencies or excessive vitamin C intake, but it’s generally not clinically significant.

You can’t directly control LDH levels, but protecting your organs and avoiding risk factors helps:

• Eat a balanced diet rich in whole foods, with minimal processed sugars and fats
• Exercise regularly, but avoid overtraining
• Avoid alcohol abuse, which can harm your liver
• Don’t smoke, as it affects lung and heart health
• Manage chronic conditions like diabetes, high blood pressure, or infections
• Get regular checkups and blood tests to detect any early issues

After the test:

• Keep the needle site clean and dry
• Avoid lifting heavy objects for a few hours if your arm feels sore
• Drink water to help flush out your system (unless told otherwise)
• Follow up with your doctor once the results are ready

If LDH levels are elevated, your healthcare provider will recommend next steps based on your symptoms and medical history. This may include imaging, additional blood work, or referral to a specialist.