Bilirubin is Most Affected by Light Exposure in Serum Specimens
Bilirubin is the analyte most affected when a non-hemolyzed, non-lipemic serum specimen is not protected from light following collection. Light exposure causes photodegradation of bilirubin, potentially leading to falsely decreased results and misdiagnosis 1, 2.
Why Bilirubin is Vulnerable to Light Exposure
Bilirubin is highly photosensitive and undergoes significant degradation when exposed to light:
- Research demonstrates that bilirubin in specimens stored in light conditions degrades at a significantly faster rate (mean 0.0020 AU/h) compared to specimens stored in dark conditions (mean 0.0005 AU/h) 1
- The photodegradation of bilirubin is not predictable or consistent, making it impossible to correct for light exposure after it occurs 1
- Unconjugated bilirubin degrades approximately twice as fast as monoconjugated bilirubin and three times faster than diconjugated bilirubin when exposed to light 2
Impact on Clinical Testing
Light exposure to serum specimens containing bilirubin can lead to:
- False-negative or falsely decreased bilirubin results
- Misdiagnosis or missed diagnosis of conditions like jaundice, liver disease, or hemolytic disorders
- Inaccurate assessment of disease severity or treatment efficacy
- Erroneous clinical decisions based on artificially lowered bilirubin values
Proper Handling of Specimens for Bilirubin Testing
To ensure accurate bilirubin measurement:
- Protect specimens from light immediately after collection using amber-colored tubes or by wrapping tubes in aluminum foil 3, 4
- Process specimens promptly, ideally within 1 hour of collection 3
- Centrifuge specimens at >2000 rpm for 5 minutes as soon as possible 3
- Store supernatant at 4°C in the dark until analysis 3
- Avoid vacuum tube transport systems when possible 3, 4
Comparison with Other Analytes
While other analytes listed in the question can be affected by various pre-analytical factors, they are not as significantly impacted by light exposure as bilirubin:
- Calcium (A): Primarily affected by anticoagulants (especially EDTA), prolonged tourniquet application, and pH changes, but not significantly by light exposure
- Glucose (B): Primarily affected by glycolysis in unpreserved specimens, temperature, and time delays, but not significantly by light exposure
- AST (C): Primarily affected by hemolysis and temperature, but not significantly by light exposure
Clinical Significance
The photodegradation of bilirubin is particularly important in:
- Neonatal jaundice assessment, where accurate bilirubin measurement guides phototherapy decisions
- Liver disease diagnosis and monitoring
- Evaluation of hemolytic disorders
- Suspected subarachnoid hemorrhage cases where CSF bilirubin measurement is critical 3, 4
The significant impact of light on bilirubin levels makes it the analyte most vulnerable to light exposure among those listed, requiring specific protective measures during specimen collection, transport, and storage to ensure accurate results.