Which urinary component is light-sensitive and may degrade with light exposure?

• A. Bilirubin
• B. Urobilinogen
• C. Glucose
• D. Ketones

Answer: (A)

Bilirubin is light-sensitive because its chemical structure readily absorbs light and undergoes photochemical breakdown. When urine containing bilirubin is exposed to light, bilirubin degrades to other products such as biliverdin, which reduces the amount detected on testing and can produce falsely low results. This is why bilirubin in urine must be protected from light—store samples in amber containers or cover them, and test promptly to avoid degradation.

In contrast, glucose and ketones are not primarily affected by light exposure in routine handling, and urobilinogen is comparatively more stable to light. The emphasis on light sensitivity points to bilirubin as the component prone to degradation with light.