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

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False-Positive and False-Negative Urobilinogen Results

A false-positive urobilinogen reaction on the reagent strip may occur when substances known to react with Ehrlich reagent are present in the urine, including porphobilinogen*, sulfonamides and p-aminosalicylic acid. Drugs that contain azo dyes, such as Azo Gantrisin®, have a gold color that masks the reaction, causing a false-positive reaction. Atypical color reactions may be obtained in the presence of high concentrations of p-aminobenzoic acid.
Due to the instability of urobilinogen, a false-negative result may occur if the urine specimen remains at room temperature and exposed to light for an extended period of time. A false-negative result may also occur if formalin is present.

*The urobilinogen reagent strip test is not a reliable method for the detection of porphobilinogen.