Enzyme Diagnostic Applications

Enzyme Diagnostic Applications - Marker Magic

• Ideal Diagnostic Enzyme Properties:

  • High organ/tissue specificity.
  • Steep concentration gradient: intracellular >> extracellular.
  • Released mainly on cell injury/death.
  • Stable in vitro for assay.
  • Easy, reliable, cost-effective assay.
  • Plasma concentration reflects damage extent.

• Plasma Enzymes:

  • Functional: Actively secreted, specific function in plasma (e.g., LCAT, clotting factors).
  • Non-Functional (Cellular): No physiological role in plasma; released from damaged cells.

    ⭐ Non-plasma functional enzymes are normally present in very low concentrations in plasma.

• Mechanisms of Enzyme Release into Plasma:

  • Cell damage/necrosis (most common).
  • Increased cell membrane permeability.
  • Increased enzyme synthesis (induction).
  • Cell proliferation (e.g., tumors).

Enzyme Diagnostic Applications - Heart Heroes

Cardiac markers for Myocardial Infarction (MI):

• CK-MB: Rises 3-6 hrs, peaks 12-24 hrs, normalizes 2-3 days. >6% of total CK. Useful for re-infarction.
• Troponins (cTnI, cTnT): Rise 2-4 hrs.
  • cTnI: Peaks ~24 hrs, normalizes 7-10 days.
  • cTnT: Peaks 24-48 hrs, normalizes 10-14 days (can be ↑ in renal failure).

  ⭐ Troponin I (cTnI) is the most specific cardiac marker for MI.

• LDH: Rises 12-24 hrs, peaks 48-72 hrs, normalizes 10-14 days. LDH1 > LDH2 flip (late marker).
• AST: Rises 6-12 hrs, peaks 24-48 hrs, normalizes 3-5 days. Non-specific.

Cardiac Marker Time Course in MI

Enzyme Diagnostic Applications - Gut Guardians

Liver Enzymes:

• ALT (Alanine Aminotransferase): Primarily liver-specific. 📌 L for ALT = Liver.
• AST (Aspartate Aminotransferase): Liver, heart, muscle, kidney.
• De Ritis Ratio ($AST/ALT$): >2 suggests alcoholic hepatitis; <1 common in viral hepatitis.
• ALP (Alkaline Phosphatase): ↑ in cholestasis, bone disease, pregnancy.
• GGT (Gamma-Glutamyl Transferase): ↑ in cholestasis, significant alcohol intake.
• 5'-Nucleotidase (5'-NT): Specific for hepatobiliary cholestasis (differentiates liver vs. bone ALP origin).

Pancreatic Enzymes:

• Amylase: ↑ early in acute pancreatitis; also salivary origin.
• Lipase: More specific & sensitive for acute pancreatitis; remains elevated longer.

Liver Injury Patterns:

⭐ GGT is a very sensitive indicator of alcohol ingestion or cholestasis, often elevated even with minor insults to the liver or biliary system.

Enzyme Diagnostic Applications - Body Detectives

Enzymes act as specific markers for disease diagnosis and monitoring.

• Bone: Alkaline Phosphatase (ALP) isoenzymes (bone, liver, placental) help identify sources of tissue damage.
• Muscle:
  • Creatine Kinase (CK) - see table.
  • Aldolase: elevated in muscle diseases.
• Prostate: Prostatic Acid Phosphatase (PAP) used in prostate cancer assessment.
• RBCs:
  • Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency: drug-induced hemolysis.
  • Pyruvate Kinase (PK) deficiency: chronic hemolysis.
• Other: ↑ Serum Amylase in acute pancreatitis and mumps.

High‑Yield Points - ⚡ Biggest Takeaways

• CK-MB and Troponins are crucial for MI diagnosis; Troponins offer higher specificity.
• LDH isoenzymes (LDH1 in MI, LDH5 in liver/muscle) help identify damaged tissue.
• ALT is more liver-specific than AST; GGT indicates cholestasis or alcohol intake.
• Elevated Amylase and Lipase (more specific) strongly suggest acute pancreatitis.
• Increased Alkaline Phosphatase (ALP) points to cholestatic liver disease or bone disorders.
• Acid Phosphatase (ACP) was a marker for prostatic carcinoma, now largely replaced by PSA.