Biochemical Investigations and Muscle Damage

Biochemical Investigation Uses

• Biochemical investigations are useful for diagnosing and monitoring disease progression.
• Principle uses include screening, diagnosis, monitoring, and prognosis.

Cellular Damage

• Most analytes used in diagnosis rely on the difference in concentration between the cell and plasma.
• Cellular damage releases the normally high concentration of intracellular analytes into the bloodstream.

Creatine Kinase (CK) and Duchenne Muscular Dystrophy

• CK is an enzyme involved in energy production present in high amounts in skeletal and cardiac muscle.
• Elevated plasma CK levels indicate muscle damage and can be more than 10 times higher than the reference range in Duchenne muscular dystrophy.
• Asymptomatic female carriers of the DMD gene often (75%) have elevated plasma CK activity.

Muscle Damage

• Causes of muscle damage include: excessive physical exercise, surgery, skeletal muscle trauma, drug-induced muscle damage (e.g., cocaine).

  General Principles of Enzyme Measurement

• Enzymes catalyze chemical reactions without being consumed, allowing for sensitive detection of small amounts in the bloodstream.

• Coupled reactions and enzyme-coupled assays are used to monitor the production of NADPH, which is then measured by absorbance change at 340nm.

Myocardial Infarction (MI)

• Infarction is the death of part or whole of an organ due to obstructed blood supply.
• An infarct is a small, localized area of dead tissue.

Plasma Enzyme Activities Following MI

• Enzyme levels rise following MI, indicating damage to cardiac tissue.

CK Isoenzymes

• CK has several different molecular forms called isoenzymes.
• Total CK assays measure all CK activity in a plasma sample, but do not distinguish between isoenzymes.
• CK isoenzymes are tissue-specific, allowing for more targeted diagnosis of specific tissue damage.
• CK-MB is primarily associated with cardiac muscle, while CK-MM is more associated with skeletal muscle.

Tests for Liver Disease

• Liver function tests assess liver cell damage, synthetic function, conjugating capacity, and cholestasis.
• Liver cell damage is indicated by elevated levels of AST and ALT.
• Synthetic function is assessed by prothrombin time and albumin levels.
• Conjugating capacity is indicated by conjugated bilirubin levels.
• Cholestasis is indicated by elevated ALP and γ-GT levels, as well as serum bilirubin.

Hepatocellular Damage

• AST and ALT are enzymes released into the bloodstream when liver cells are damaged.
• ALT is more liver-specific than AST, which can be elevated in other tissues as well.

Choleostasis

• Choleostasis is the failure of normal bile flow to the intestine.
• ALP and γ-GT enzymes normally anchor to hepatocyte membranes but are released in choleostasis.
• γ-GT is more liver-specific than ALP, which can also be elevated in bone disease.
• Changes in γ-GT and ALP levels often parallel each other in choleostatic disease.

Causes of Increased Plasma AST

• High AST levels, over 10 times the upper limit of normal (ULN), are often associated with acute hepatitis, liver necrosis, major crush injuries, severe tissue hypoxaemia, and myocardial infarction.
• Moderate AST levels, 5-10 times ULN, can indicate skeletal muscle disease, cholestasis, chronic hepatitis, and physiological elevations (neonates).

Commonly Used Biochemical Techniques

• Various methods and techniques are used to measure analytes in body fluids.

Biochemical Investigations For Diagnosis and Monitoring Disease Progression

• Biochemical investigations play a crucial role in diagnosing and monitoring disease progression.
• They can help detect subclinical disease, confirm or reject clinical diagnoses, monitor the natural history of a disease, and assess response to treatment.
• Biochemical measurements depend on the high concentration of a substance within a cell relative to its concentration in plasma.
• Levels of analytes such as proteins, enzymes, or other molecules in plasma can indicate cellular damage or dysfunction.

General Principles of Enzyme Measurement

• Enzymes are biological catalysts that increase the rate of chemical reactions without being consumed themselves.
• A small amount of enzyme released into the bloodstream can be detected with great sensitivity.
• The activity of an enzyme is determined by its ability to convert a substrate into a product.
• Coupled reactions are used to measure enzyme activity.
• Isoenzymes are different molecules that catalyze the same reaction, but have different structures and tissue distributions.
• Isoenzymes can be distinguished by their electrophoretic mobility, different activities towards different substrates, or other properties.

Creatine Kinase (CK) and Muscle Damage

• Creatine kinase (CK) is an enzyme present in muscle tissue that catalyzes the conversion of creatine phosphate to creatine.
• Increased CK levels in the blood may indicate muscle damage.
• The CK-MB isoenzyme is specifically elevated in myocardial infarction.
• Other causes of elevated CK levels include strenuous exercise, surgery, trauma, and drug use.

Distribution of Clinically Important Enzymes

• Different enzymes are found in various tissues.
• The distribution of an enzyme can help pinpoint the source of damage.
• For example, increased levels of acid phosphatase indicate damage to the prostate gland.
• Other enzymes like alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) are used to assess liver function.

Liver Enzymes

• The liver plays a crucial role in metabolism, synthesis, and excretion.
• Liver damage can be assessed by measuring levels of enzymes such as ALT, AST, ALP, and gamma-glutamyl transferase (GGT).
• ALT, AST, and GGT are released into the bloodstream when liver cells are damaged.
• Elevated ALP levels indicate cholestasis, a condition where bile flow is blocked.

Measuring Analytes in Body Fluids

• Various techniques are used to measure analytes in body fluids.
• Common methods include spectrophotometry, chromatography, and electrophoresis.
  ### Study Notes for "Common methods" Continued
• Spectrophotometry measures the absorption of light by a substance.
• Chromatography separates substances based on their physical properties.
• Electrophoresis separates substances based on their charge and size.