Which factor could falsely increase the measured urobilinogen on a dipstick?

• A. Light exposure
• B. Ascorbic acid
• C. Porphobilinogen presence
• D. High SG

Answer: (C)

When a dipstick measures urobilinogen, it relies on a color reaction that can be triggered by substances with similar chromogenic properties. Porphobilinogen is a porphyrin-related compound that can react with the same dye used in the test, producing a color that mimics urobilinogen. This cross-reactivity leads to a reading that appears higher than the true urobilinogen level. Light exposure tends to degrade colored substances like bilirubin rather than raise the urobilinogen signal, and ascorbic acid often interferes by diminishing color (causing false negatives rather than false positives). High specific gravity may alter intensity by concentration but doesn’t specifically cause a false increase in urobilinogen.