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 with some methods when the concentration of ascorbic acid is greater than 5 mg/dL. The sensitivity of the blood portion of the test strip is decreased in specimens with a high specific gravity and increased protein. High levels of nitrites may delay the reaction, causing a false negative to be reported. If the pH of a urine sample is below 5, hemolysis of red cells as part of the test reaction is inhibited which results in a false negative reaction. An improperly mixed specimen may test negative if the red blood cells are in the sediment.