The day 4 bilirubin result, given daily controls were in range, most likely resulted from which factor?

• A. No explanation necessary
• B. Serum, not plasma, was used for testing
• C. Prolonged exposure to light
• D. Specimen was hemolyzed

Answer: (C)

Bilirubin is highly sensitive to light, so prolonged exposure to light can alter its measurement. When a sample sits in light, bilirubin undergoes photodegradation and photoisomerization, forming products like lumirubin that many common bilirubin assays don’t detect in the same way. This can cause the measured bilirubin to fall, even though the sample and assay are functioning properly (as indicated by in-range daily controls). Therefore, the most likely factor is that the specimen was exposed to light for an extended period. To avoid this, protect bilirubin samples from light from collection through analysis, using amber tubes or wrappers and minimizing light exposure during transport and storage.