Activity of human and nonhuman amylases on different substrates used in enzymatic kinetic assay methods--a pitfall in...

Many commercial kits have been marketed recently for the determination of amylase activity in clinical specimens by enzymatic kinetic methods. Oligosaccharides (e.g., maltotetraose or maltopentaose) or limit dextrin are used as substrates. Hydrolysis of the substrate is coupled through a series of enzymes to convert NAD+ to NADH which is measured at 340 nm. Commercially available controls and standards for the amylase test consist of pooled human sera supplemented with human, porcine, or bovine amylase. The authors tested various control sera and standards by six commercial kits. Sera supplemented with porcine or bovine pancreatic amylase gave significantly lower values when assayed by methods using maltotetraose as substrate than when assayed by methods using maltopentaose or other oligosaccharides as substrate. Sera supplemented with human salivary amylase gave comparable results by five of the six methods. Results were comparable by all six methods for serum specimen supplemented with human pancreatic amylase. These kinetic methods are superior to the older amyloclastic, saccharogenic, or dye-coupled starch methods and are expected to gain popularity among clinical laboratories. The authors recommend that quality control programs designed to evaluate interlaboratory performances consider the use of human pancreatic amylase to supplement their serum specimens.