LDH Blood

What Is an LDH Blood Test?

An LDH blood test, or lactate dehydrogenase test, is a diagnostic tool used in medicine to measure lactate dehydrogenase levels, an enzyme, in a patient's blood. LDH is an enzyme found in various tissues and organs throughout the body, including the heart, liver, muscles, kidneys, and red blood cells. This blood test is often employed to assess the extent of tissue damage or disease affecting these organs.

The LDH enzyme is crucial in converting lactate to pyruvate, an essential step in cell energy production. When tissue damage, such as from injury, infection, inflammation, or diseases like heart disease, liver disease, or muscular dystrophy, the cells release LDH into the bloodstream. Consequently, this blood test can detect and quantify elevated LDH levels, indicating tissue damage.

Doctors use LDH blood tests for various clinical purposes, such as assessing cardiac health, diagnosing liver diseases, and identifying muscle disorders. The tests can also be conducted to monitor the effectiveness of cancer treatments or detect hemolysis.

Interpreting the test results requires considering the patient's overall health, medical history, and other diagnostic tests. An abnormal LDH level does not provide a specific diagnosis but is a valuable indicator of underlying health issues, helping healthcare professionals make informed decisions regarding further evaluation and treatment. 

How Does it Work?

The LDH blood test, or lactate dehydrogenase test, is a laboratory procedure that assesses the levels of the LDH enzyme in a patient's blood. This test is relatively simple, and here are the key steps involved in conducting an LDH blood test:

Patient Preparation

The patient may need to fast for a specific period before the test, as instructed by the healthcare provider. It's essential to inform the healthcare professional about any patient's medications or supplements, as some can influence the test results.

Blood Sample Collection

A healthcare provider, typically a nurse or phlebotomist, cleans the patient's skin and inserts a needle into a vein, usually in the arm, to collect a blood sample. The blood is drawn into a special tube designed for laboratory testing.

Sample Processing

The blood sample is then processed in a clinical laboratory.

Enzyme Activity Measurement

The LDH enzyme's activity in the laboratory is measured using a chemical reaction that converts lactate to pyruvate. The rate of this reaction is directly proportional to the LDH activity in the blood.

Data Analysis

The laboratory technician or an automated machine quantifies the LDH levels in the blood sample.

Result Reporting

The test results are reported in units per liter (U/L) or as a ratio, depending on the specific method used in the laboratory.

Interpretation

The healthcare provider interprets the LDH levels regarding the patient's health and medical history.

Clinical Implications

Elevated LDH levels may indicate tissue damage or disease in various organs or tissues, prompting further evaluation and diagnostic tests. Normal LDH levels are reassuring but do not rule out other health issues.

Follow-up

Based on the LDH test results and other clinical information, the healthcare provider may recommend additional tests, imaging, or treatment as necessary.

When Would You Use This Test?

The LDH blood test, or lactate dehydrogenase test, is used by healthcare practitioners in specific clinical scenarios to diagnose and monitor various medical conditions. Here's a focused overview of when it is appropriate to use the LDH blood test:

• Cardiac Events: The LDH blood test is crucial in assessing suspected heart conditions, especially during acute events like myocardial infarction (heart attack) or myocarditis. It helps identify cardiac muscle damage.
• Liver Diseases: Hepatologists and gastroenterologists utilize the test to diagnose and monitor liver diseases such as hepatitis and cirrhosis, where elevated levels indicate liver damage.
• Oncology: Oncologists frequently order the test to aid in cancer diagnosis and treatment monitoring, particularly in lymphoma, leukemia, and metastatic cancers, as elevated levels can indicate tumor activity.
• Autoimmune Disorders: Rheumatologists use LDH tests to assess patients with autoimmune diseases, such as systemic lupus erythematosus and vasculitis, where elevated levels may provide valuable diagnostic insights.
• Muscle-Related Issues: Orthopedic surgeons and neurologists may request LDH tests to evaluate muscle damage or disorders, particularly in traumatic injuries and conditions like muscular dystrophy.
• Primary Care Settings: General practitioners use tests as a broad marker of tissue damage, which helps identify underlying health issues and guides further evaluation.
• Emergency Medicine: Emergency room physicians rely on tests to diagnose and assess the extent of tissue damage in patients with traumatic injuries, suspected heart attacks, or other acute medical conditions.
• Kidney Function: Nephrologists use tests to evaluate kidney function, as elevated levels can indicate kidney damage.
• Hematological Disorders: Hematologists may order tests in cases of hemolytic anemias, where red blood cells are prematurely destroyed, leading to increased levels.

What do the Results Mean?

Interpreting LDH blood test results is crucial in understanding a patient's health condition. Elevated or abnormal LDH levels can suggest underlying issues, while normal levels are generally reassuring. Here's a breakdown of what common LDH blood test results may indicate:

• Normal Range: The LDH range typically falls between 140 to 280 U/L (units per liter), but specific reference ranges may vary between laboratories. Normal results indicate no significant tissue damage or disease affecting the organs that release LDH.
• Slightly Elevated LDH Levels: Slight increases in levels may not cause immediate concern and can result from factors such as strenuous exercise. However, mild elevations may warrant further investigation in the context of clinical symptoms.
• Moderately Elevated LDH Levels: Elevated LDH may indicate tissue damage or disease. For example, in cases of myocardial infarction (heart attack), LDH levels can be significantly elevated.
• Markedly Elevated LDH Levels: Marked increases in levels are often seen in severe tissue damage or disease. For instance, in advanced liver disease or extensive muscle injuries, LDH levels can be significantly elevated.
• Ratios and Isoenzymes: LDH has different isoenzymes, or subtypes, which are found in various tissues. By examining the ratio of LDH isoenzymes, healthcare providers can pinpoint the source of LDH elevation. An elevated LDH-1 level, for example, might suggest heart or red blood cell issues, while an LDH-5 elevation may indicate liver problems.
• Dynamic Changes: Serial LDH measurements over time can provide valuable information. Increasing levels may indicate worsening tissue damage, while decreasing levels may suggest successful treatment or healing.

It's essential to note that while the blood test results can raise suspicion of tissue damage or disease, they are not specific to a particular condition. Additional diagnostic tests, medical history, and clinical symptoms are often required to determine the underlying cause accurately.

Research & Evidence

The enzyme lactate dehydrogenase (LDH) was first identified in the early 20th century. Its presence in various tissues and cells was recognized as part of the burgeoning field of biochemistry.

LDH as a diagnostic tool gained momentum in the mid-20th century. It was initially employed to assess tissue damage, particularly in heart attacks and liver diseases.

LDH became one of the early cardiac biomarkers to diagnose myocardial infarctions (heart attacks). Elevated LDH levels in the blood were associated with cardiac muscle damage. Subsequent research refined its role in cardiac diagnostics and established its use alongside other cardiac markers like troponin.

Research demonstrated the value of LDH as an adjunct in diagnosing and prognosis of various cancers. Elevated LDH levels in certain cancers, such as lymphomas and leukemia, were linked to tumor activity. This evidence led to its inclusion in cancer diagnostic panels.

Research has consistently shown the utility of LDH in assessing liver function and detecting liver diseases. Elevated LDH levels are associated with liver damage, hepatitis, and cirrhosis, supporting its use in hepatology.

Studies have explored the role of LDH in diagnosing autoimmune diseases, such as systemic lupus erythematosus and vasculitis, where elevated LDH levels have been noted in some patients.

In hematology, LDH is used to evaluate hemolytic anemias, where red blood cells are destroyed prematurely, increasing LDH levels. Research supports its utility in this context.

Evidence indicates that LDH can be valuable in monitoring disease progression and the response to treatment, helping clinicians make informed decisions.

References

• Lu, C. M., MD PhD. (2022, December 6). Lactate dehydrogenase (LDH) test - Testing.com. Testing.com. https://www.testing.com/tests/lactate-dehydrogenase-ldh/
• Mph, Z. S. (2023, March 2). Lactate dehydrogenase (LDH) test: Uses and results. https://www.medicalnewstoday.com/articles/ldh
• Polymed Lab. (n.d.). LDH >. https://polymedlab.ph/products/ldh
• Vergel, N. (2023, May 5). Understanding the LDH blood test. Discounted Labs. https://www.discountedlabs.com/blog/Understanding-the-LDH-Blood-Test