Moving to practice with the application of Milan model 1b-based analytical performance specifications

The definition of analytical performance specifications (APS) by the Milan model 1b is based on indirect approaches investigating the impact of analytical performance of the laboratory test on clinical classification and thereby on the probability of patient outcomes. As direct diagnostic outcome studies (Milan model 1a) for defining APS are now considered very difficult and costly to be performed in practice, expert groups have gathered to reach consensus on how to use available information and apply Milan model 1b to the definition of APS. They have highlighted three major aspects: a) the definition of the clinically acceptable misclassification rate(s); b) the influence of the clinical pathway and patient population and setting (disease prevalence) when diagnostic thresholds are defined, e.g., in guidelines; and c) the intended use of the test. The basic question calling for an answer is how to move forward and provide specific APS for certain measurands that are key in clinical decision making. Here, cardiac troponin testing is used as a practical example for the application of model 1b-derived APS. Proposals are made for moving to practice with the application of this model to APS definition.