What substance in urine is affected by exposure to light or photo-oxidation?

Bilirubin is the substance in urine that is notably affected by exposure to light or photo-oxidation. When urine containing bilirubin is exposed to light, it undergoes a breakdown process, leading to a decrease in its concentration. This occurs because bilirubin can be converted to photobilirubin and other photoproducts when exposed to light.

In clinical practice, this is a significant consideration, especially during urine collection and storage. If bilirubin is present in a urine sample and is subjected to light, the resulting degradation may lead to inaccurate laboratory results, potentially obscuring liver function assessment or the presence of hemolysis in patients.

Other substances listed have different properties and stability in urine. Urobilin, while also related to bilirubin metabolism, is generally stable and does not undergo degradation in the same manner due to light exposure. Creatinine is a stable endogenous compound that does not degrade over time or with light exposure. Albumin, a protein, is similarly not affected by light in the context of its measurement in urine.