Introduction
The LDH Test (Lactate Dehydrogenase Test) is a valuable diagnostic tool that helps assess cell damage and tissue injury in the body.
LDH (Lactate Dehydrogenase) is an enzyme found in almost every cell and tissue. It plays a vital role in energy production, and its presence in the bloodstream serves as a key marker of cellular damage.
Whenever cells are destroyed or injured, LDH leaks into the blood, leading to elevated levels. Because LDH is present in almost all organs — including the heart, liver, kidneys, muscles, and lungs — it is a non-specific indicator of disease but still provides important diagnostic clues.
What is LDH (Lactate Dehydrogenase)?
LDH (Lactate Dehydrogenase) is an enzyme that helps the body convert lactate into pyruvate during energy metabolism (glycolysis). It is essential for maintaining energy balance in cells, especially when oxygen levels are low.
When cells are damaged, LDH escapes from within the cells into the bloodstream. This makes LDH a valuable biochemical marker for various conditions such as heart attack, liver diseases, lung disorders, blood diseases, and cancers.
Key Features:
- Found in nearly every cell of the body.
- Released during tissue damage or inflammation.
- Non-specific marker — can increase due to multiple causes.
- Used in cancer monitoring, cardiac evaluation, and liver disease assessment.
Where is LDH Produced in the Body?
LDH is not synthesized in one specific organ — rather, it exists naturally inside cells throughout the body. It is present in higher concentrations in:
- Heart
- Liver
- Kidneys
- Lungs
- Skeletal muscles
- Red Blood Cells (RBCs)
Each organ contains slightly different forms (called isoenzymes) of LDH. When certain tissues are damaged, the pattern of isoenzyme elevation helps identify which organ is affected.
Main Functions and Importance of LDH
1. Energy Production
LDH plays a crucial role in the glycolytic pathway — it catalyzes the conversion of lactate to pyruvate and vice versa.
This process helps cells produce energy when oxygen supply is limited (for example, during intense exercise or in poorly oxygenated tissues).
2. Marker of Tissue Damage
LDH is released into the bloodstream whenever cells rupture or die.
Therefore, elevated LDH levels indicate cellular injury, such as those caused by heart attacks, liver disease, muscle injury, or hemolysis (red blood cell breakdown).
3. Cancer Marker
LDH is also used as a tumor marker in certain cancers, including:
- Lymphoma
- Leukemia
- Germ cell tumors (testicular/ovarian)
- Metastatic cancers
Higher LDH levels may suggest aggressive disease, tissue destruction, or poor oxygen supply in tumors.
4. Diagnostic and Monitoring Tool
LDH assists doctors in:
- Evaluating liver or lung function
- Assessing anemia due to red blood cell destruction
- Diagnosing pancreatitis
- Monitoring treatment response in cancer patients
Causes of Low LDH Levels
Low LDH levels are rare and usually not clinically important.
Possible Causes:
- High intake of Vitamin C: Can interfere with LDH test results, giving falsely low readings.
- Genetic LDH Deficiency (rare): May cause fatigue and exercise intolerance, as cells struggle to generate enough energy.
Symptoms of Low LDH
- Usually no symptoms (as it’s uncommon).
- In rare LDH deficiency: muscle weakness or fatigue during exercise.
Causes of High LDH Levels
High LDH indicates cellular damage or tissue breakdown. It can occur in a wide variety of conditions, both mild and serious.
Common Causes of Elevated LDH:
1. Heart Diseases
- Myocardial infarction (Heart Attack): Damaged heart muscle releases LDH (especially LDH-1 and LDH-2).
- Heart failure: Due to ongoing tissue injury.
2. Liver Diseases
- Hepatitis, Cirrhosis, Liver injury, or Liver metastasis can all raise LDH.
3. Blood Disorders
- Hemolytic anemia: Destruction of red blood cells releases LDH into plasma.
- Megaloblastic anemia: Associated with abnormal cell turnover.
4. Muscle Disorders
- Muscle trauma, crush injuries, or muscular dystrophy can cause elevated LDH.
- Severe physical exertion can also temporarily increase LDH.
5. Lung Diseases
- Pneumonia, Pulmonary embolism, and lung infarction may elevate LDH-3 levels.
6. Kidney Diseases
- Renal infarction or acute kidney injury releases LDH into the blood.
7. Cancer
- Lymphomas, leukemias, and germ cell tumors often show high LDH levels.
- LDH is a prognostic marker in cancer — higher levels often correlate with disease severity or metastasis.
8. Other Causes
- Sepsis, pancreatitis, or infections.
- High physical activity (temporary rise).
Symptoms of High LDH
LDH itself does not produce symptoms. The signs depend on the underlying condition that caused the elevation.
| Possible Cause | Common Symptoms |
|---|---|
| Heart attack | Chest pain, shortness of breath, sweating |
| Liver disease | Jaundice, fatigue, nausea, abdominal pain |
| Anemia | Pale skin, weakness, dizziness |
| Lung disease | Cough, breathlessness, chest pain |
| Cancer | Unexplained weight loss, night sweats, fever |
Reference Ranges of LDH (Lactate Dehydrogenase)
| Group | Normal Range (U/L) |
|---|---|
| Adults | 140 – 280 U/L |
| Newborns | Up to 450 U/L (normal in early life) |
LDH Isoenzymes (5 Types and Their Major Locations):
| Isoenzyme | Tissue Source |
|---|---|
| LDH-1 | Heart, RBCs |
| LDH-2 | Reticuloendothelial system |
| LDH-3 | Lungs |
| LDH-4 | Kidneys, pancreas, placenta |
| LDH-5 | Liver, skeletal muscle |
Note: The specific LDH isoenzyme pattern can help pinpoint the source of tissue damage (e.g., LDH-1 rise indicates heart or red blood cell damage).
Sample Type
- Sample Type: Serum (blood)
- Tube Used: Red-top (plain) tube
- Test Type: Enzyme activity measurement (U/L)
- Fasting: Not required
Test Preparation
- No fasting required.
- Avoid intense physical exercise before testing, as it can temporarily raise LDH levels.
- Inform the doctor about any ongoing infections, medications, or supplements (especially Vitamin C).
When to Consult a Doctor
You should consult a doctor if:
- Your LDH levels are elevated without clear cause.
- You experience chest pain, jaundice, fatigue, or unexplained weight loss.
- You have a known condition such as anemia, liver disease, or cancer, and LDH is being used for monitoring.
- You have recurring muscle pain or weakness after exercise (possible LDH deficiency).
Important Word Explanations
| Word | Meaning |
|---|---|
| LDH (Lactate Dehydrogenase) | Enzyme involved in energy production; rises when cells are damaged. |
| Isoenzymes | Different forms of the same enzyme found in various tissues. |
| Hemolysis | Breakdown of red blood cells. |
| Cirrhosis | Chronic liver damage causing scarring. |
| Lymphoma | Cancer of lymphatic tissues. |
| Myocardial Infarction | Medical term for heart attack. |
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