A blood test result can contain many acronyms. Among them, the LDH line might draw attention if its value is outside the normal range. It’s natural to wonder about the meaning of this marker. Understanding what lactate dehydrogenase is and why it’s measured is the first step to becoming an informed participant in your own health journey. This article aims to provide clear and factual explanations about this biological parameter, its role in the body, and the interpretation of its variations.

What is LDH (Lactate Dehydrogenase)?

Lactate dehydrogenase, or LDH, is an enzyme found in almost all human body cells. An enzyme is a protein that accelerates chemical reactions necessary for life. LDH plays a central role in energy metabolism. It participates in the conversion of pyruvate to lactate. This reaction is crucial for enabling cells to produce energy, especially when oxygen supply is limited.

Where is LDH found?

All tissues produce LDH, but some contain higher concentrations. This is the case for organs and cells with high metabolic activity, such as the heart, liver, muscles, kidneys, brain, and red blood cells.

There are five different forms of this enzyme, called isoenzymes (LDH-1 to LDH-5). Each isoenzyme predominates in specific tissues. For example, LDH-1 is primarily cardiac, while LDH-5 is mainly hepatic and muscular. This specificity sometimes helps doctors locate the origin of a lesion.

Why measure this level?

LDH measurement is an indicator of cellular integrity. When cells are damaged or destroyed, they release their contents into the bloodstream. LDH is part of this content. Therefore, an increase in its level in the blood is a non-specific signal of tissue damage somewhere in the body. It is a sensitive marker but always requires interpretation within a global clinical context.

Why is LDH monitoring important?

LDH is a general health marker because it reflects the state of many tissues. Its elevation can occur in a wide range of situations, from myocardial infarction to hepatitis. In some cases, an abnormal and persistent elevation may be the first sign of an undiagnosed pathology. It is therefore important to investigate any significant and lasting anomaly of this parameter.

In oncology, doctors recognize LDH as a prognostic marker for certain tumors. They associate high levels with a larger tumor mass or accelerated tumor metabolism. Consequently, they use variations in LDH levels to assess a patient’s response to certain treatments: a decrease indicates good chemotherapy efficacy, while a new increase suggests a recurrence.

How to read and understand your LDH results

On a laboratory report, LDH is found in the biochemistry section. The result is presented with the measured value and reference values.

Understanding reference values

The unit of measurement is International Units per Liter (IU/L). Normal values vary depending on the laboratory, techniques used, and the patient’s age. In adults, the reference range is generally between 140 and 280 IU/L. It is essential to always refer to the norms indicated on your own analysis bulletin.

A value outside this range is often indicated by a color or symbol. The magnitude of the deviation should then be observed. Your doctor is the only one who can interpret this result, taking into account your symptoms, your medical history, and other parameters of your blood count.

Pathologies linked to variations in LDH levels

An abnormal LDH value can be a sign of various situations.

Elevation of the level

Cardiac pathologies

A myocardial infarction causes the death of cardiac cells. These then release LDH (mainly LDH-1). The level increases within 24 to 48 hours and remains elevated for several days. More specific markers like troponins are now used as a first-line approach.

Hepatic pathologies

Liver damage, such as viral or toxic hepatitis, leads to the destruction of liver cells. This causes a significant release of LDH (especially LDH-5). This elevation is usually accompanied by that of other liver enzymes (AST, ALT).

Hematological pathologies

Certain anemias, called hemolytic anemias, are characterized by an accelerated destruction of red blood cells. Since these cells are rich in LDH, their massive destruction causes a sharp increase in blood levels.

Tumor pathologies

Many cancers can lead to an elevation of LDH. This reflects the rapid turnover of malignant cells and their particular metabolism. It is an important monitoring marker for lymphomas or melanoma, for example.

Muscle injuries

Significant muscle trauma, surgery, or muscle disease (myopathy) can cause the destruction of muscle fibers and thus the release of LDH.

Decrease in the level

Doctors sometimes observe a decrease in the level — a rare and generally not concerning phenomenon — in patients who consume very large amounts of vitamin C (which can interfere with the assay) or who have certain exceptional genetic diseases.

Practical advice and level monitoring

What monitoring schedule?

The frequency of monitoring depends on the level of the anomaly and the clinical context.

• Slight and isolated elevation: A check after 1 to 3 months may be sufficient, avoiding physical exertion before the blood draw.
• Moderate elevation: A medical consultation is recommended. The doctor will suggest a follow-up check at a few weeks’ interval.
• Strong elevation: A prompt consultation is necessary to perform additional examinations without delay.

What lifestyle modifications?

Good lifestyle habits support overall tissue health.

• For athletes: Plan for adequate recovery after intense efforts. Avoid having a blood test right after a competition.
• For sedentary individuals: Incorporate moderate and regular physical activity, such as 30 minutes of walking per day.
• Stress management: Techniques like deep breathing or meditation can help reduce chronic inflammation.
• Diet: A diet rich in antioxidants (colorful fruits, vegetables) and omega-3s (fatty fish, nuts) and low in ultra-processed products and alcohol is beneficial for liver and cardiovascular health.

Frequently Asked Questions

Is an elevated LDH always a sign of disease?

No. Intense physical exercise within 48 hours preceding the test can normally increase LDH. Another common cause of “false” elevation is in vitro hemolysis. This means that red blood cells were damaged in the tube after collection, releasing their LDH.

How does the doctor find the origin of an LDH elevation?

Interpretation is based on the context: symptoms, clinical examination, and other biological results. If necessary, the doctor may request an assay of LDH isoenzymes. The predominance of certain fractions (LDH-1, LDH-5, etc.) points towards a specific tissue or organ.

Can certain medications influence LDH levels?

Yes. Several medications can cause liver or muscle toxicity and thus increase LDH. This is the case with certain statins, some anesthetics, or anticonvulsants. It is therefore crucial to always inform your doctor of all ongoing treatments.

Is LDH a follow-up marker for cancer?

Yes, in certain cancers, LDH is a useful prognostic and follow-up marker. Its evolution (decrease, stabilization, or increase) during and after treatment provides indications of the tumor’s response and can help detect recurrence.

Additional resources

• To deepen your knowledge of this blood marker, click here.
• To extend your knowledge and decipher other markers, more articles are available here.

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