LDH (Lactate Dehydrogenase): Understanding Your Blood Test

What Is LDH?

Lactate dehydrogenase (LDH) is an enzyme found in nearly every cell of the body. It plays an important role in energy production, helping convert sugar into usable energy during a process called anaerobic metabolism. Because LDH is present in so many tissues—including the heart, liver, muscles, kidneys, lungs, blood cells, and brain—it can serve as a general marker of cell damage or turnover.

When cells are injured or destroyed, they release LDH into the bloodstream. For this reason, an elevated LDH level often signals that some form of tissue damage may be occurring somewhere in the body, though it does not, on its own, identify where or why. LDH is considered a nonspecific marker, meaning it must always be interpreted alongside your symptoms, history, and other laboratory results.

What the Test Measures

The standard LDH blood test measures the total amount of the enzyme circulating in your blood serum. In certain situations, your clinician may order additional testing to look at the five different forms of LDH, known as isoenzymes (LDH-1 through LDH-5). Each isoenzyme is more concentrated in particular tissues:

• LDH-1 and LDH-2: heart, red blood cells, and kidneys
• LDH-3: lungs and other tissues
• LDH-4 and LDH-5: liver and skeletal muscle

Measuring specific isoenzymes can sometimes help narrow down the source of an elevated total LDH, though this specialized testing is used less frequently in modern practice.

LDH Reference Ranges

Reference ranges can vary between laboratories depending on the equipment and methods used. Age also affects normal values, and children and newborns typically have higher levels. Always compare your result to the range listed on your own lab report.

Because laboratory methods differ, some labs report adult ranges that fall slightly above or below the values shown here. Your report will specify the range that applies to your test.

What High Levels Can Mean

An elevated LDH suggests that cells may be being damaged or broken down, but it does not pinpoint the cause. Higher-than-normal LDH may be associated with a wide range of conditions, including:

• Tissue injury or trauma
• Certain infections
• Liver conditions such as hepatitis
• Heart-related tissue damage
• Muscle injury or breakdown
• Anemia, including the breakdown of red blood cells (hemolysis)
• Kidney or lung conditions
• Some cancers and blood disorders
• Recent strenuous exercise

It is important to note that a technical issue during blood collection—such as red blood cells rupturing in the sample tube (hemolysis)—can falsely raise LDH results. Because so many factors can influence this enzyme, an elevated LDH almost always requires follow-up testing and professional interpretation to understand its significance.

What Low Levels Can Mean

Low LDH levels are uncommon and are usually not a cause for concern. In rare cases, very low LDH may be linked to certain genetic conditions or high intake of large amounts of vitamin C (ascorbic acid). A single low reading typically does not signal a health problem, but your clinician can help interpret it in the context of your overall picture.

How the Test Is Done

The LDH test is performed on a routine blood sample. A healthcare professional draws blood from a vein in your arm, and the sample is sent to a laboratory for analysis. No special preparation is usually required, though your clinician may give you specific instructions.

Because vigorous physical activity can temporarily raise LDH, it may be helpful to avoid strenuous exercise before your test if advised. Handling of the sample also matters: gentle collection and prompt processing help prevent artificially high results caused by red blood cell breakdown within the tube.

Putting Your Number in Context

At ENNU Life, we view laboratory results as part of a larger story rather than isolated numbers. A single LDH value tells you very little on its own—the more meaningful insight comes from understanding your result within the full context of your health, your symptoms, and your other biomarkers.

Our approach emphasizes looking beyond the standard “normal” range toward optimal function and, when appropriate, identifying the root cause behind an abnormal reading. Because LDH is a nonspecific marker, an elevated result is best understood as a signal that invites further investigation rather than a diagnosis in itself.

We also believe in the value of tracking trends over time. Comparing your LDH across multiple tests can reveal whether a value is stable, rising, or improving—information that a single snapshot cannot provide. Small fluctuations within the reference range are common and often reflect normal variation, recent activity, or minor differences in how a sample was handled.

Ultimately, any decision about additional testing or treatment should be made together with your clinician, who can integrate your LDH result with your complete health history. If your LDH is outside the expected range, your clinician may recommend repeat testing or additional evaluation to clarify what is driving the change.