False Negative Results

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The page below is a sample from the LabCE course Chemical Screening of Urine by Reagent Strip (retired March 2012). Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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False Negative Results

False negative results may occur in urine specimens that did not remain in the bladder a sufficient length of time for the bacteria to reduce a measurable quantity of nitrate to nitrite. Other reasons for false negative results include high specific gravity, ascorbic acid levels above 25mg/dL or low pH (<6). Less frequently, the cause may be due to a lack of sufficient nitrate in the diet (green vegetables) or further reduction of nitrite to nitrogen when large numbers of bacteria are present. In patients receiving antibiotics, the metabolism of the bacteria may be inhibited which would also produce a false negative reaction.