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The investigation determined that higher than expected free t4 (ft4) results were obtained from a patient sample and from a vitros free thyroid quality control fluid when running vitros ft4 reagent on a vitros 5600 integrated system.The assignable cause of the event was incorrect preparation of the vitros ft4 calibrators.All unexpected results were obtained on calibration curves from calibrators that were prepared using reagent grade water.Per the vitrso ft4 instructions for use (ifu), distilled water is to be used for reconstitution.When the customer prepared the calibrators per the ifu, the patient and controls results were within expectation.Vitros ft4 reagent lot 5240 was a new lot at the customer site and therefore historical qc was not available, however the initial biorad qc run on this lot and the vitros ft4 qc were higher than expected when processed on the calibration that was not made per ifu specifications using reagent grade water.When a calibration was performed per ifu specifications using distilled water, results for both the biorad qc and the vitros ft4 qc were within expectation.A diagnostic vitros tt4 precision test was acceptable, indicating that unexpected instrument performance is not a likely contributor to the event.Continual tracking and trending of complaints has not identified any signals that would indicate a potential systematic issue with vitros ft4 reagent lot 5240.
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