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The investigation has determined that lower than expected results were obtained from two different levels of vitros therapeutic drug monitoring performance verifier (tdm pv) fluids and two different patient samples using the vitros valproic acid (valp) assay and one level of vitros tdm pv fluid and one different patient sample using the vitros vancomycin (vanc) assay.The affected samples were tested using vitros valp reagent lot 2511-32-1564 and vitros vanc lot 2514-54-1972 which were processed on a vitros xt 7600 integrated system.The assignable cause of the lower than expected results for each assay was a reagent pack related issue.The affected vitros valp results were isolated to a single reagent pack, pack id 339, and the affected vitros vanc results were isolated to a single reagent pack, pack id 9851.The cause of the issue with the affected reagent packs is unknown, as both reagent packs were discarded by the customer and no further investigation was possible.With the exception of the single affected vitros valp and vanc reagent packs, there was no indication that vitros valp reagent lot 2511-32-1564 or vitros vanc reagent lot 2514-54-1972 was not performing as intended, based on historical quality control results.Acceptable results were obtained from the same vitros tdm pv fluids using the vitros acet, crbm, phyt and dgxn assays, indicating there was not a performance issue associated with the vitros tdm pv fluids in use.There is no indication the vitros xt 7600 integrated system malfunctioned as acceptable vitros valp and vanc performance was obtained using alternate reagent packs of the same lot numbers without performing any actions to optimize instrument performance.This indicates the vitros xt 7600 integrated system did not likely contribute to the event.
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