Laboratory proficiency in testing for antibodies to Mycobacterium avium subspecies paratuberculosis: A new approach for the United States

摘要

The goal of proficiency testing for antibodies to Mycobacterium avium subspecies paratuberculosis (MAP) is to assure users that laboratories are able to conduct serology testing in a way that will provide quality results to be used in the Voluntary Bovine Johne's Disease Control Program. Historically, the panel of 25 sera, including some duplicates, was graded based on qualitative (positive/negative) results. Qualitative scoring of test results will often lead to selection of a panel of sera that give extreme values (positive or negative) to avoid challenges of the interpretation around the cutpoint of the test. The Z-scoring system, which is currently used in Australia, can be used to score quantitative outcomes of tests and has the potential to be modified and adopted for use with many laboratory tests. A combination of positive/negative and Z-scoring has been adopted by the United States for MAP ELISA antibody testing. The Z-scoring system uses the median and inter-quartile range values from the participating labs' results in the analysis. This Z-score can then used to evaluate inter- and intra-laboratory variation in ELISA readings. Graphical representation of summed Z-scores may assist labs in identifying and resolving laboratory errors. The combination of scoring methods should provide more assurance in the quality of MAP antibody results for the US and has the potential to improve laboratory proficiency.