A-114 Effect of light exposure on the stability of total and direct bilirubin in plasma

Abstract Background Bilirubin is a key biomarker for liver function assessment, with both total bilirubin (TBIL) and direct bilirubin (DBIL), commonly measured in clinical laboratories. Clinicians are dependent upon reliable bilirubin results for appropriate diagnosis and treatment. Bilirubin is known to undergo photodegradation when exposed to light, which may impact the result accuracy and therefore appropriate diagnoses and treatment. However, the extent of TBIL and DBIL degradation over time under different storage conditions has not been well characterized. This study evaluates the stability of TBIL and DBIL in de-identified plasma specimens stored under controlled conditions with and without light exposure for up to 72 hours. Methods De-identified plasma specimens with TBIL concentrations ranging from 0.5 mg/dL to 20.2 mg/dL and DBIL concentrations ranging from 0.2 mg/dL to 13.5 mg/dL were analyzed approximately 1 hour from collection. Specimens were either wrapped in aluminum foil (control, no light exposure) or exposed to laboratory ambient light. Two storage conditions were assessed: refrigeration (REF, 2–8°C) and room temperature (RT, 20–25°C). TBIL and DBIL concentrations were measured at baseline, 8, 24, 48, and 72 hours using a validated method on a Cobas 8000 c702 chemistry analyzer (Roche Diagnostics). TBIL and DBIL stability were assessed by calculating the percent change from baseline across conditions and time points. Results After 72 hours, TBIL and DBIL exhibited varying degrees of stability depending on storage conditions. In control samples, TBIL remained relatively stable, with an average change of -0.29% (range: -16.34% to 10.45%) at RT and 3.60% (range: -2.98% to 10.61%) under REF. In contrast, DBIL showed greater inherent instability, decreasing by -25.11% (range: -66.01% to -2.94%) at RT and -9.33% (range: -30.28% to 5.88%) at REF. Light exposure significantly accelerated the degradation of both analytes. After 72 hours, TBIL levels decreased by -72.63% (range: -88.46% to -32.34%) at RT and -65.66% (range: -90.00% to -22.29%) at REF. Similarly, DBIL declined by -67.58% (range: -74.19% to -47.33%) at RT and -56.59% (range: -73.53% to -26.35%) at REF. Conclusion This study highlights the differential stability of TBIL and DBIL under various storage conditions over 72 hours. While TBIL exhibited relatively minor fluctuations in control samples, DBIL demonstrated greater inherent instability, particularly at room temperature. The most pronounced degradation occurred with light exposure, leading to substantial reductions in both analytes, regardless of temperature. These findings underscore the critical importance of proper sample handling, including protection from light and appropriate storage temperatures, to maintain the accuracy of bilirubin measurements in clinical practice.