False-Positive and False-Negative Urobilinogen Results
A false positive urobilinogen reaction may occur with the chemical reagent strip method when substances known to react with Ehrlich's reagent such as sulfonamides and p-aminosalicylic acid are present in the urine. 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.
The chemical reagent strip urobilinogen test cannot detect porphobilinogen in a urine specimen. Porphobilinogen is a molecule formed during the synthesis of the heme portion of hemoglobin.
Due to the instability of urobilinogen, a false negative result may occur using the chemical reagent strip method if the urine specimen has remained at room temperature for an extended period of time exposed to light. A false negative result may also occur if formalin is present.