The investigation determined that higher than expected vitros sodium (na+) results were obtained from vitros performance verifier (pv) i q1174 using vitros na+ slide lot 4212-1097-6151 on a vitros 5600 integrated system.The assignable cause of the event could not be determined.Pre-analytical sample mix-up was a potential cause of the event; however, the customer could not confirm it occurred.Historical quality control results indicated that within-lab imprecision was present prior to the event, therefore, a performance issue with vitros na+ slide lot 4212-1097-6151 cannot be ruled out as contributing to the event.Further investigation was not possible as the inventory of the slide lot was depleted at the site.However, continual tracking and trending of complaints has not identified any signals that would point to a potential systemic issue with vitros na+ slide lot 4212-1097-6151.Acceptable vitros na+ performance was obtained with an alternate vitros na+ slide lot 4217-1103-9397.A performance issue with the vitros 5600 integrated system did not likely contribute to the event as within-run vitros na+ precision testing using vitros na+ slide lot 4217-1103-9397 was acceptable, without performing any actions to optimize the instrument.
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