Aged urine samples left at room temperature and exposed to UV light may cause a false negative result in which one of the following biochemical tests?

Aged urine samples left at room temperature and exposed to UV light may cause a false negative result in which one of the following biochemical tests?

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

Answer: (D)

Bilirubin in urine is photosensitive, so it degrades when exposed to light, especially UV, and as the sample ages at room temperature. The urine bilirubin test relies on a color-forming reaction (diazo reaction) that detects intact bilirubin. When bilirubin photodegrades, the color development weakens or disappears, leading to a false negative—even if bilirubin is present. The other tests use chemistry that isn’t as rapidly disrupted by light exposure or aging, so they’re less likely to give false negatives under these conditions. To prevent this, protect urine samples from light and test promptly or refrigerate if delays are expected.

Bilirubin in urine is photosensitive, so it degrades when exposed to light, especially UV, and as the sample ages at room temperature. The urine bilirubin test relies on a color-forming reaction (diazo reaction) that detects intact bilirubin. When bilirubin photodegrades, the color development weakens or disappears, leading to a false negative—even if bilirubin is present. The other tests use chemistry that isn’t as rapidly disrupted by light exposure or aging, so they’re less likely to give false negatives under these conditions. To prevent this, protect urine samples from light and test promptly or refrigerate if delays are expected.