Setting process control limits for enzyme tests in serum.

With the advent of much more precise laboratory equipment, the use of performance-based standard deviations for enzymes, e.g. those based on the precision of the laboratory during a period of "satisfactory performance", is not appropriate; it leads to overly rigid precision limits and unnecessary repeat assays, and is wasteful of resources. Testing for the commonly used serum enzymes does not require tight precision given how enzyme data are viewed by most clinicians. Other ways to set process control limits all have some arbitrary content; however, this need not prevent their use. Laboratorians must choose the approach that is appropriate for their laboratory and medical staff to meet medically perceived needs.