Proposal for the modification of the conventional model for establishing performance specifications

Abstract

Appropriate quality of test results is fundamental to the work of the medical laboratory. How to define the level of quality needed is a question that has been subject to much debate. Quality specifications have been defined based on criteria derived from the clinical applicability, validity of reference limits and reference change values, state-of-the-art performance, and other criteria, depending on the clinical application or technical characteristics of the measurement. Quality specifications are often expressed as the total error allowable (TE A ) -the total amount of error that is medically, administratively, or legally acceptable. Following the TE A concept, bias and imprecision are combined into one number representing the "maximum allowable" error in the result. The commonly accepted method for calculation of the allowable error based on biological variation might, however, have room for improvement. In the present paper, we discuss common theories on the determination of quality specifications. A model is presented that combines the stateof-the-art with biological variation for the calculation of performance specifications. The validity of reference limits and reference change values are central to this model. The model applies to almost any test if biological variation can be defined. A pragmatic method for the design of internal quality control is presented.

Useful measures and models for analytical quality management in medical laboratories

“…It is important to distinguish these application models from goal-setting models. A criticism of the model for calculating ATE from components of biologic variation [37,38] doesn't negate the usefulness of ATE goals for analytical quality management.…”

“…Setting Bias a based on CV i and CV g makes use of the Gowan's model and the effects of analytical performance on maintaining common reference intervals [36] and minimizing misclassification of patients. Combining these two maximum specifications to calculate a biologic ATE has been criticized [37] and one of the new proposals from the Milan conference is a model that combines state-of-the-art and biologic variation [38]. The proposed new model would overcome situations where biologic goals are too demanding, which is a limitation for measurands such as sodium, calcium, etc., that are very tightly controlled physiologically.…”

The use of error and uncertainty methods in the medical laboratory

“…Oosterhuis and Sandberg [33] adapted the model of Gowans et al [28] to include the influence of analytical variation on the reference interval. Even inclusion of analytical variation, however, might lead to an underestimation of the actual reference interval limits, e.g.…”

“…The conventional linear model (expression 1) has been criticized for a number of reasons [5]: 1. Both maxima of permissible bias and imprecision are added to obtain pTAE, a pragmatic solution first proposed for the use in proficiency testing [33]. The theoretical basis for this is lacking.…”

Total error vs. measurement uncertainty: revolution or evolution?

“…The ratio of bias and imprecision should be known for the estimation of ATE in those mixed models [8] and the effects of these factors on the total error of the measurement in theory need to be separated. However, this can only be done in retrospect, and not at the instance of the interpretation of the latest results of the internal quality control.…”