Allowable limits of performance – statistical basis and implementation

Abstract

In external quality assurance programs (EQA) the analytical goal is determined by the acceptable range about the central value. Some EQA programs around the world use a statistically determined range, such as two standard deviations from the mean value of returned results, to determine the acceptable range. This gives the laboratory information to compare their performance to the performance of other laboratories but does not relate the laboratory result to the clinical management of the patient. In the Royal College of Pathologists of Australasia (RCPA) Chemical Pathology Quality Assurance Programs (QAP) the acceptable range is determined by the allowable limits of performance (ALP). The ALP is related to clinical need. A result outside the acceptable range may compromise the clinical management of the patient. ALPs have been used by the QAP since its inception in 1982 and up until recently these have been determined by expert opinion. However there now exists an internationally agreed hierarchy of preferred methods for establishing performance goals and using biological inter- and intravariability is a higher order method to expert opinion. After much discussion the QAP has begun the process of revising the ALPs based on biological variability. The considerations that are taken into account and the implementation will be discussed in detail.