The customer's test strips and analyzer were requested and returned for investigation.The customer's test strips, lot 42219903, had an expiration date of 30-nov-2020.The customer's test strips showed no abnormalities.The customer's analyzer and tray were clean and showed no damages.Due to the customer's test strips being expired once received for an investigation, the investigation used retention test strips for testing.The customer's urisys 1100 urine analyzer, an investigation's urisys 1100 analyzer, and an investigation's cobas u411/urisys 1800 were measured with randomly selected retention material lot 51950500 with of 0-native-urine and an erythrocytes-dilution-series.Neither the retention analyzers nor the customer's analyzer showed any false-negative results.Per product labeling, "false negative readings are obtained when formalin is used to preserve the urine or on medications with nitrofurantoin and quinidine." also, "nitrite in excess of 10 mg/dl in the urine (which is rare in urinary tract infections) delays the reaction" and "medications with 2-mercaptoethanesulphonatesodium (mesna) can lead to false positive or false negative reading of reagent pad color change." under the performance section, "a field study of 637 freshly voided urine specimens in routine diagnosis produced no false-negative results and in only a small percentage of cases, recorded a higher erythrocyte concentration than the ten-field sediment method." the investigation did not identify a product problem.The cause of the event could not be determined.Updated medwatch fields d9 and h3.
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