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The investigation concludes that a higher than expected result above the vitros amon measuring range of 8.7 - 500 umol/l was obtained from a single patient sample using vitros ammonia (amon) slide lot 1020-0268-5975 on a vitros 4600 chemistry system.The assignable cause of the event was a suboptimal calibration.A review of the calibration responses and parameters indicated the calibration was atypical when compared to the release calibration responses and parameters.The cause of the atypical calibration could not be determined with the information provided.The customer provided no details concerning the calibrator fluid handling, therefore, it is possible that improper fluid handling protocol contributed to the event, although this could not be confirmed.The customer does not process quality controls to assess the performance of the vitros amon assay or to verify calibrations.Therefore, it was not possible to assess assay performance and a performance issue with vitros amon slide lot 1020-0268-5975 cannot be ruled out as contributing to the event.Continual tracking and trending of complaints has not identified any signals that would point to a potential systemic performance issue with vitros amon slide lot 1020-0268-5975.An instrument related performance issue cannot be ruled out as contributing to the event as no diagnostic within-run precision testing to assess instrument performance was performed.No information was provided concerning the affected sample or how the sample was collected, processed and stored prior to testing.Therefore, it was not possible to establish if the customer is following the sample collection device manufacturer recommendation for sample centrifugation therefore improper pre-analytical sample handling could have contributed to this event.It is possible that cellular debris, due to poor sample preparation, was present in the affected sample, although this could not be confirmed.
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