Chapter 7 - Clinical Enzymology and Biomarkers of Tissue Injury

Abstract

Enzymes in circulating plasma are either plasma-specific or non-plasma-specific. Plasma-specific enzymes, normally present in plasma, perform their primary functions in blood. Non-plasma-specific enzymes are intracellular enzymes, their concentrations are low or undetectable under normal conditions, but undergo elevations due to tissue injury and damage. Plasma levels of secretory enzymes increase when their cells of origin undergo damage or membrane impairment, or when the usual pathways of enzyme secretion are obstructed. The diagnosis of organ disease is aided by the measurement of a number of enzymes characteristic of that tissue or organ. Most tissues have characteristic enzyme patterns that may be reflected in the changes in serum concentrations of these enzymes in disease. Moreover, many enzymes have isoenzyme forms, which have relative tissue specificity, the measurement of these isoenzyme levels facilitates the diagnosis of a specific tissue injury. Factors that affect the plasma or serum enzyme activities include: rate of cell turnover, increased synthesis due to normal growth and repair, or stimulation of synthesis or degradation by drugs, and the clearance rate of enzymes in circulation.