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The investigation determined that lower than expected vitros phenobarbital (phbr) results were obtained from a single american proficiency institute (api) proficiency survey sample when processed using vitros phbr slide lots: 2517-0117-7418 and 2517-0117-7396 on a vitros xt 7600 integrated system.The assignable cause of the event could not be determined with the information provided.Historical vitros phbr lot: 1 and lot: 2 qc results showed some inaccuracy and imprecision, therefore an issue with either of these lots cannot be ruled out as a potential contributor to the event.However, continual tracking and trending of complaints has not identified any signals that would point to a potential systemic issue with vitros phbr slide lots: 2517-0117-7418 and 2517-0117-7396.An instrument-related performance issue cannot be ruled out as contributor to the event, as no diagnostic precision testing was performed to assess instrument performance.Therefore, an issue with the vitros xt 7600 integrated system cannot be confirmed or ruled out as a contributor to the event.Additional troubleshooting including processing calibrator fluids as patients, and a patient comparison between vitros phbr calibrations and lots was requested from the customer, however this has not been completed at the time of this report.Although the calibrations in use at the time the vitros phbr repeat results were obtained showed some atypical parameters, the qc imprecision observed by the customer would not be affected by calibration.As the customer is observing both inaccuracy with their l3 fluid and imprecision on both levels, it is possible that a suboptimal calibration could contribute to inaccurate results, while the cause of the imprecision could be from another factor.However, this could not be confirmed at this time with the information provided.
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