Insufficient harmonization of antibiotics assays - Polish experience with an external quality assessment program in the years 2011-2018.

INTRODUCTION: Treatment with vancomycin and gentamycin requires strict monitoring of its serum concentration for proper dosage optimization. This study aimed to assess the quality and the harmonization of antibiotics assays in Polish laboratories.

MATERIALS AND METHODS: 413 results of vancomycin and 148 results of gentamycin assays obtained from Polish laboratories in 30 international external quality assessment (EQA) surveys carried out from March 2011 to May 2018 were analyzed.

RESULTS: Interlaboratory rCVs in particular surveys comprised between 1.3 and 47.2% for vancomycin, and between 1.8 and 34.2% for gentamycin. The percentage of the results with the difference above acceptable limit ±10% from the target value established for own method group was 25.7% for vancomycin and 25.6% for gentamycin. When the difference was established according to target value for all methods, the percentage of results outside the acceptable limit was 2-fold higher on average (54.8% for vancomycin and 43.2% for gentamycin). The comparison of target values for methods revealed statistically significant differences between analytical systems used (p < .0001). The highest difference was 40% for vancomycin and 12% for gentamycin.

CONCLUSIONS: The present analysis revealed high dispersion of the antibiotics assays results in Polish laboratories. Moreover, vancomycin and gentamycin results differed significantly in a way dependent on the analytical system used. There appear to be an urgent need for harmonization of methods used for vancomycin and gentamycin measurement.