Chapter 18: Plasma Enzymes in Diagnosis (Clinical Enzymology)

Plasma Enzymes in Diagnosis (Clinical Enzymology) establishes that plasma enzyme levels represent a dynamic equilibrium between the rate of cellular release—often accelerated by necrosis, proliferation, or enzyme induction—and the rate of systemic clearance. A significant portion of the text is dedicated to the clinical utility of isoenzymes, which are molecular variants that allow for greater diagnostic precision by localizing damage to specific organs, such as the heart, liver, or skeletal muscle. Key biomarkers discussed include the aminotransferases (ALT and AST) for hepatic and cardiac assessment, creatine kinase (CK) and its MB fraction for muscular and myocardial pathologies, and alkaline phosphatase (ALP) for evaluating bone and hepatobiliary disorders. The text also covers the diagnostic challenges posed by macroenzymes—large complexes often bound to immunoglobulins—and the importance of considering non-pathological variables such as age, sex, ethnicity, and analytical factors like pH and temperature during interpretation. Furthermore, it details specialized enzymatic assessments, including amylase and lipase for pancreatic health, gamma-glutamyl transferase (GGT) as a marker of enzyme induction or cholestasis, and the significance of plasma cholinesterase variants in predicting adverse reactions to anesthetic agents like suxamethonium. By integrating these enzymatic patterns with clinical presentations, healthcare professionals can better differentiate between conditions ranging from acute viral hepatitis and rhabdomyolysis to myocardial infarction and various malignancies.