INTERPRETATION OF CARDIAC ENZYMES

Introduction

Cardiac enzymes, also known as cardiac biomarkers, are proteins released into the blood when the heart muscle is damaged due to various conditions such as myocardial infarction (heart attack), cardiomyopathy, or other forms of heart disease. The levels of these enzymes can provide valuable information for diagnosing and monitoring cardiac conditions. Here are some common cardiac enzymes and their interpretations:

1. Troponin:

Troponin is the most commonly used cardiac enzyme for diagnosing heart attacks. It is released from the damaged heart muscle cells and can be detected in the blood within 4-6 hours of the onset of symptoms. Troponin levels increase with the severity of the heart attack, and they can remain elevated for several days after the event.

2. Creatine Kinase (CK):

Creatine kinase is an enzyme found in various tissues, including the heart. When the heart muscle is damaged, CK is released into the blood, indicating a potential heart problem. However, CK levels can also be elevated due to other conditions such as muscle strain or kidney disease.

3. Brain Natriuretic Peptide (BNP):

Brain natriuretic peptide is a hormone produced by the heart in response to stress or injury. Elevated BNP levels can indicate heart failure, especially when combined with other symptoms such as shortness of breath or swelling.

In conclusion, the interpretation of cardiac enzymes requires careful consideration of the patient’s symptoms, medical history, and other diagnostic tests. These enzymes can provide valuable insights into the underlying cause of cardiac problems, but they should not be relied upon solely for diagnosis. A healthcare professional should always be consulted for proper evaluation and treatment.

 

Release of CPK, LDH and SGOT during a heart attack

When the heart muscle cells are injured, such as during a heart attack, certain cardiac enzymes are released into the bloodstream. These enzymes include creatine phosphokinase (CPK), lactate dehydrogenase (LDH), and serum glutamic-oxaloacetic transaminase (SGOT), also known as aspartate aminotransferase (AST).

1) CPK, also referred to as creatine kinase, is an enzyme found predominantly in the heart, brain, and skeletal muscles. There are three isoenzymes of CPK: CPK-MB (found mainly in the heart), CPK-MM (found in skeletal muscles), and CPK-BB (found in the brain). During a heart attack, the damaged heart muscle cells release CPK-MB into the bloodstream. Therefore, elevated levels of CPK-MB in the blood indicate myocardial injury.

2) LDH is an enzyme that exists in various tissues throughout the body, including the heart. It plays a crucial role in energy production by converting lactate to pyruvate. LDH has five isoenzymes: LDH-1 to LDH-5. LDH-1 and LDH-2 are primarily found in the heart, while LDH-3 is found in both the lungs and red blood cells. During a heart attack, there is an increase in LDH-1 levels due to the release of this specific isoenzyme from damaged heart muscle cells.

3) SGOT, or AST, is an enzyme that catalyzes the transfer of an amino group from aspartate to alpha-ketoglutarate. It is present in various tissues, including the liver, heart, skeletal muscles, kidneys, and brain. However, SGOT is particularly abundant in cardiac tissue. When there is damage to the heart muscle cells, SGOT is released into the bloodstream, leading to elevated levels of this enzyme.

The release of these cardiac enzymes occurs due to the disruption of the cell membrane integrity in injured heart muscle cells. During a heart attack, the blood supply to a part of the heart muscle is blocked, resulting in ischemia (lack of oxygen and nutrients). This lack of oxygen leads to cellular injury and death, causing the release of intracellular components, including enzymes, into the bloodstream.

The measurement of these cardiac enzymes, particularly CPK-MB and LDH-1, is commonly used in clinical practice as diagnostic markers for myocardial infarction (heart attack). Elevated levels of CPK-MB and LDH-1 in the blood can indicate recent myocardial injury. However, it is important to note that these enzymes are not specific to heart muscle damage and can also be elevated in other conditions such as skeletal muscle injury or liver disease.

In summary, when heart muscle cells are injured during a heart attack, certain cardiac enzymes such as CPK-MB, LDH-1, and SGOT are released into the bloodstream. These enzymes serve as diagnostic markers for myocardial injury and are measured to assess the extent of damage to the heart muscle.

 

Levels of cardiac enzymes in the blood

Cardiac enzymes play a crucial role in the diagnosis of a heart attack and assessing the extent of damage done to the heart. The most commonly measured cardiac enzymes include troponin, creatine kinase (CK), also known as creatine phosphokinase (CPK), lactate dehydrogenase (LDH), and serum glutamic-oxaloacetic transaminase (SGOT), also known as aspartate aminotransferase (AST).

1. Troponin: Troponin is considered the gold standard cardiac enzyme for diagnosing a heart attack. It is a protein found in cardiac muscle cells and is released into the bloodstream when these cells are damaged. There are three types of troponin: troponin I (cTnI), troponin T (cTnT), and troponin C (cTnC). Among these, cTnI and cTnT are most commonly measured in clinical practice.

Elevated levels of troponin in the blood indicate myocardial injury or damage. Troponin levels start to rise within 3-4 hours after the onset of a heart attack, peak at around 24-48 hours, and can remain elevated for up to two weeks. Higher levels of troponin generally indicate more severe damage to the heart muscle.

2. Creatine Kinase (CK) / Creatine Phosphokinase (CPK): CK is an enzyme found in various tissues, including skeletal muscle, brain, and heart muscle. It exists as three different isoforms: CK-MM (found in skeletal muscle), CK-MB (found predominantly in the heart), and CK-BB (found mainly in the brain).

In the context of a heart attack, CK-MB is the specific isoform that is measured. Elevated levels of CK-MB in the blood indicate myocardial damage. CK-MB levels start to rise within 3-6 hours after a heart attack, peak at around 12-24 hours, and return to normal within 48-72 hours. CK-MB is less specific for cardiac injury compared to troponin and can also be elevated in other conditions such as skeletal muscle injury.

3. Lactate Dehydrogenase (LDH): LDH is an enzyme found in various tissues, including the heart. It exists as five different isoforms: LDH-1 (predominantly found in the heart), LDH-2, LDH-3, LDH-4, and LDH-5. The ratio of LDH-1 to LDH-2 is often used to assess cardiac involvement.

Elevated levels of LDH in the blood can indicate myocardial damage. However, LDH lacks specificity for cardiac injury and can also be elevated in other conditions such as liver disease or hemolysis. LDH levels start to rise within 12-24 hours after a heart attack, peak at around 48-72 hours, and gradually return to normal over several days.

4. Serum Glutamic-Oxaloacetic Transaminase (SGOT) / Aspartate Aminotransferase (AST): SGOT, also known as AST, is an enzyme found in various tissues, including the heart, liver, skeletal muscle, and kidneys. Elevated levels of SGOT in the blood can indicate myocardial damage.

However, SGOT lacks specificity for cardiac injury and can also be elevated in other conditions such as liver disease or skeletal muscle injury. SGOT levels start to rise within 6-12 hours after a heart attack, peak at around 24-48 hours, and return to normal within 3-5 days.

It is important to note that while these cardiac enzymes are valuable in diagnosing a heart attack and assessing the extent of damage, they should be interpreted in conjunction with clinical symptoms, electrocardiogram (ECG) findings, and other diagnostic tests such as coronary angiography.

In summary, the levels of cardiac enzymes such as troponin, CK/CPK, LDH, and SGOT are commonly measured to aid in the diagnosis of a heart attack and evaluate the extent of damage done to the heart. Troponin is considered the most specific and sensitive marker for myocardial injury, while CK-MB, LDH, and SGOT provide additional information but lack specificity. Interpretation of these enzyme levels should be done in conjunction with other clinical findings and diagnostic tests.

 

Overview of Normal Range and Elevated Levels of Troponin, CK/CPK, LDH and SGOT

1) Normal Range and Elevated Levels of Troponin:

Troponin is a protein found in cardiac muscle cells and is released into the bloodstream when there is damage to the heart muscle. It is commonly used as a biomarker for diagnosing and monitoring acute myocardial infarction (heart attack). Troponin levels are measured using highly sensitive assays, and the results are reported in nanograms per milliliter (ng/mL).

The normal range for troponin levels varies slightly depending on the specific assay used, but generally, a level below 0.04 ng/mL is considered normal. Elevated levels of troponin indicate cardiac injury or stress. The degree of elevation can provide information about the severity of the injury. In general, troponin levels above the 99th percentile upper reference limit (URL) are considered abnormal.

2) Normal Range and Elevated Levels of CK (Creatine Kinase) and CPK (Creatine Phosphokinase):

CK, also known as CPK, is an enzyme found in various tissues, including skeletal muscle, heart muscle, and brain tissue. It plays a crucial role in energy metabolism. CK exists in three isoforms: CK-MM (skeletal muscle), CK-MB (heart muscle), and CK-BB (brain tissue). The total CK level represents the sum of these isoforms.

The normal range for total CK varies depending on the laboratory and the specific assay used. In general, the normal range for total CK is around 30-200 units per liter (U/L). However, it’s important to note that individual isoforms may have different reference ranges.

Elevated levels of CK can occur due to various conditions such as muscle injury or disease, myocardial infarction, brain injury, or strenuous exercise. The degree of elevation and the specific isoform affected can provide valuable diagnostic information. For example, an elevated CK-MB level is suggestive of myocardial damage.

3) Normal Range and Elevated Levels of LDH (Lactate Dehydrogenase):

LDH is an enzyme found in many tissues, including the heart, liver, kidneys, and red blood cells. It plays a role in converting lactate to pyruvate during energy metabolism. LDH exists in five isoforms: LDH-1 (heart), LDH-2 (reticuloendothelial system), LDH-3 (lungs), LDH-4 (kidneys), and LDH-5 (liver).

The normal range for LDH varies depending on the laboratory and the specific assay used. In general, the normal range for total LDH is around 100-250 U/L. However, the relative proportions of the different isoforms can provide additional diagnostic information.

Elevated levels of LDH can occur due to various conditions such as tissue damage, inflammation, infection, or certain cancers. The degree of elevation and the specific isoform affected can help identify the underlying cause.

4) Normal Range and Elevated Levels of SGOT (Serum Glutamic Oxaloacetic Transaminase):

SGOT, also known as AST (aspartate aminotransferase), is an enzyme found primarily in the liver, heart, skeletal muscle, and kidneys. It plays a role in amino acid metabolism. SGOT levels are measured in units per liter (U/L).

The normal range for SGOT varies depending on the laboratory and the specific assay used. In general, the normal range for SGOT is around 10-40 U/L for adults. However, it’s important to note that certain factors such as age, sex, and underlying medical conditions can influence the reference range.

Elevated levels of SGOT can occur due to various conditions such as liver disease (e.g., hepatitis), heart muscle damage (e.g., myocardial infarction), skeletal muscle injury, or certain medications. The degree of elevation can provide valuable diagnostic information.

It’s important to note that these ranges may vary slightly depending on the laboratory and the specific test used. Additionally, these values are not diagnostic of any specific condition, and should be interpreted in conjunction with other clinical findings and medical history.