An example of using enzymes as reagents in the clinical laboratory is

• A. The hexokinase glucose method
• B. The diacetyl monoxime blood urea nitrogen (BUN) method
• C. The alkaline picrate creatinine method
• D. The biuret total protein method

Answer: (A)

Enzymatic reagents in the clinical lab use a specific enzyme-catalyzed reaction to generate a measurable signal that reflects the amount of the analyte. The glucose measurement using hexokinase illustrates this: hexokinase first transfers a phosphate from ATP to glucose, forming glucose-6-phosphate, and then glucose-6-phosphate dehydrogenase converts that product to a form that reduces NAD+ to NADH. The amount of NADH produced is proportional to the glucose concentration and can be read spectrophotometrically, giving a highly specific and accurate result with minimal interference. The other choices rely on purely chemical reactions rather than enzymes, such as a diacetyl monoxime reaction for BUN, an alkaline picrate reaction for creatinine, and the Biuret method for total protein. These non-enzymatic methods tend to be less specific and more prone to interferences, which is why the enzymatic hexokinase glucose method is the best example of using enzymes as reagents.