Enzymes as Reagents in Clinical Chemistry

Clinical chemistry is concerned with the measurement of substances in biological matter, predominantly blood, serum or plasma. Significant, though small, changes may take place as a prelude to a life-threatening situation. Therefore analytical techniques in clinical chemistry must be sensitive, specific and rapid. Many features of an enzyme-catalysed reaction are incorporated in the design of diagnostic reagents. The specificity of an enzyme may be employed to measure a substrate, or to remove interferents in another reaction. The measurement of substances that act as cofactors, inhibitors or activators can be achieved by the use of the appropriate enzyme. Finally, the enzyme, as a catalyst, can be used as a label in various immunoassay techniques. Clinical chemistry tests are carried out in a wide variety of environments, from the large laboratory undertaking many hundreds of analyses down to a clinic performing only a few tests. Enzymes are therefore employed in analytical systems based on widely differing presentations. Thus enzymes may be employed in a solution medium, immobilized on a surface of the reaction vessel or in a reagent strip. The requirements imposed on the reagent enzyme may be different in all of these situations.