LDH (Lactate Dehydrogenase): What It Is and Results

What is LDH?

Lactate dehydrogenase (LDH) is an enzyme involved in glucose metabolism — it catalyzes the conversion of pyruvate to lactate and vice versa. It is one of the key participants in the cellular energy production process.

LDH is found in nearly all body tissues: the heart, liver, kidneys, muscles, lungs, brain, and blood cells. There are five LDH isoforms (LDH-1 through LDH-5), each predominantly found in different organs. For example, LDH-1 is mainly found in the heart and red blood cells, while LDH-5 is found in the liver and skeletal muscles.

When cells of any organ are damaged or destroyed, the LDH they contain is released into the blood. Therefore, elevated LDH in the blood is a nonspecific but important marker of tissue damage. It does not answer the question of where exactly the problem is, but it signals that a pathological process is occurring somewhere in the body.

Normal ranges

The normal total LDH level in the blood for adults is typically:

• 125–220 U/L

These ranges may vary slightly depending on the laboratory, reagents used, and analytical methods, so it is always important to compare your results with the reference values provided by the specific laboratory.

It is important to keep in mind that LDH levels can be falsely elevated due to hemolysis — the breakdown of red blood cells during sample collection or transport. If the laboratory notes that the sample was hemolyzed, the result should be interpreted cautiously or the test repeated.

In children and newborns, normal LDH values are higher than in adults, so pediatric results are evaluated according to age-adjusted reference ranges.

Why it may be elevated

Since LDH is present in many tissues, an elevated level in the blood can have various causes.

Cardiovascular diseases — myocardial infarction, heart failure, or myocarditis can raise LDH levels because the heart muscle is damaged.

Liver diseases, such as hepatitis, cirrhosis, or liver damage from drugs or toxins, are often associated with elevated LDH.

Hematological conditions — hemolytic anemia (when red blood cells are broken down more intensely), megaloblastic anemia (related to vitamin B12 or folic acid deficiency) can significantly increase LDH.

Infectious diseases, especially those with a more severe course, can cause tissue damage and correspondingly increase LDH levels.

Lung diseases, including pulmonary embolism or pneumonia, may also be associated with elevated LDH.

Intense physical exertion, especially prolonged or high-intensity exercise, can temporarily raise LDH due to microtrauma to muscle cells.

Oncological diseases — LDH is often used as one of the nonspecific markers to help monitor the course of certain tumors.

Why it may be low

Low LDH levels in the blood are rare and usually have no significant clinical importance.

Genetic factors — rare inherited mutations of LDH subunits can lead to reduced enzyme activity. Such conditions are usually asymptomatic and discovered incidentally.

High levels of ascorbic acid (vitamin C) in the body may in some cases suppress LDH activity in laboratory testing.

It should be emphasized that low LDH itself rarely causes concern and usually does not require further investigation unless other clinical signs are present.

What to do next

If your LDH result is elevated, it is important not to panic — this is a nonspecific marker that does not indicate a specific disease on its own.

First, consider possible simple causes: did you recently exercise intensely, are you suffering from an infectious illness, or could the sample have been hemolyzed?

Your doctor may order additional tests to help determine the cause of the LDH elevation: LDH isoform analysis, complete blood count, liver function markers, cardiac markers, or other specific tests depending on the clinical situation.

If the LDH elevation is minor and there are no other symptoms or abnormalities in tests, the doctor may recommend repeating the test after a few weeks to assess whether the change was temporary.

Monitoring over time

Monitoring LDH over time is especially valuable because it allows you to see trends. A single result does not always reflect the true situation — temporary fluctuations are normal.

If LDH was elevated due to a specific cause (for example, an infection or physical exertion), a repeat test helps confirm that the value has returned to normal and the issue has resolved.

In the case of chronic diseases, periodic LDH measurements can help the doctor assess disease progression and treatment effectiveness.

Over time, your personal LDH history provides the doctor with much more valuable information than individual measurements.

Questions for your doctor

• What could be the cause of my elevated LDH, considering my other test results and symptoms?
• Is it necessary to perform an LDH isoform analysis to more precisely determine the site of damage?
• Should I repeat the LDH test after some time, and if so, when?
• What additional tests would help clarify my situation?
• Could my medications or lifestyle factors have influenced my LDH result?