The investigation determined that lower than expected vitros ft4 results were obtained from three patient samples, using vitros immunodiagnostics products ft4 reagent lots 3860 and 3910 processed on two vitros 5600 integrated systems (s/ns (b)(4)).A definitive assignable cause could not be determined.Based on historical quality control results for reagent lots 3860 and 3910, a vitros ft4 performance issue is not a likely contributor to the event.Since two different vitros 5600 integrated systems were affected, it is unlikely that an instrument related issue contributed to the event.The most likely assignable cause is a sample integrity or sample storage issue.The samples were left at room temperature for approximately 16 hours before being stored refrigerated at 2¿8 c.The vitros ft4 instructions for use (ifu) states that serum samples may be stored for up to 7 days at 2¿8 c (36¿46 f) or 4 weeks at -20 c (-4 f).However, the ifu also states that samples should be returned to 2¿8 c (36¿46 f) storage as soon as possible after use.The customer did not store the samples as described in the ifu.
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