External quality control in haematological morphology: a method to assess the performance of an individual laboratory...

A method is described to assess the performance of individual laboratories in estimating blood cell morphology by microscopy. The method was designed for the Finnish interlaboratory proficiency testing programme in haematological morphology. The method is based on the following principles: (1) on application of a detailed result form to collect the results from the participants in a standardized manner and (2) on application of a reference board to establish the morphological 'truth'. A consensus of greater than or equal to 80% of the reference board of haematology experts is the prerequisite for acceptance of a morphological detail as a 'target finding' for the participants. For each proficiency testing survey a score 'mean percentual performance' (MPP) was calculated for each participating laboratory. The MPP score indicates the percentual amount of correct identifications of the 'target findings' of the survey specimens and is an overall measure of performance of an individual laboratory. A running MPP graph was plotted to evaluate the changes in the performance over a course of time. Different types of 'performance profiles' among the participants were detected with this method. The merits of the MPP scoring method are discussed with special reference to the goals of external quality control in haematological morphology.