A false-positive urobilinogen reaction on the Multistix 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 high concentrations of p-aminobenzoic acid.
A false-negative reaction may occur on the Chemstrip in high concentrations of nitrite.
Due to the instability of urobilinogen, a false-negative result may occur for both strips if the urine specimen remains at room temperature and is exposed to light for an extended period. A false-negative result may also occur if formalin is present.
*The urobilinogen reagent strip test is not a reliable method for detecting porphobilinogen.
