The investigation determined that higher than expected vitros phenytoin (phyt) results were obtained on a patient sample and a quality control (qc) fluid and a higher than expected vitros carbamazepine (crbm) result was obtained from a patient sample when tested using vitros chemistry products phyt slides and vitros chemistry products crbm slides in combination with two different vitros 5600 integrated systems.The most likely assignable cause of the event was a sample related issue.The affected patient correlation samples appeared to be slightly viscous, although no sample metering condition codes were generated when the samples were processed.In addition, some samples may have been stored refrigerated for up to 2 weeks.However, the samples used for the vitros phyt correlation were plasma samples stored refrigerated on average for 7 days, while the vitros crbm correlation were plasma samples stored refrigerated on average for 5 days.Per the vitros phyt instructions for use (ifu), samples can be stored refrigerated for =7 days, while per the vitros crbm ifu, samples can be stored refrigerated for =5 days.Improper sample handling could not be ruled out as contributing to the event as no information was provided concerning the centrifugation procedure or if the samples were centrifuged a second time prior to the retesting events.It is possible that cellular debris, due to poor sample preparation, was present in the affected samples, although this could not be confirmed.A review of vitros phyt quality control results processed on (b)(4) did show some imprecision within the timeframe of the event.Therefore, an instrument or slide related issue cannot be completely ruled out for the higher than expected vitros phyt results.Ongoing tracking and trending of complaints has not identified any signals that would suggest there is a systemic issue with either vitros phyt reagent lot 2617-0168-2514 or vitros crbm reagent lot 3942-0102-0838.The customer later processed four alternate patient samples and both biorad qc levels on analyzer (b)(4) using both lots of immunowash fluid (iwf) and vitros phyt slides.They also ran an additional four patient samples and both biorad qc levels on analyzer (b)(4) using both lots of iwf and vitros crbm slides.All correlation patient results were deemed acceptable.
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