Which value represents the reference range for total bilirubin?

• A. B1: 0.2-0.8 mg/dL
• B. B2: 0-0.2 mg/dL
• C. Total: 0.2-1.0 mg/dL
• D. Overt Jaundice: Total >3 mg/dL

Answer: (C)

Total bilirubin reflects the sum of indirect (unconjugated) and direct (conjugated) bilirubin in the blood. The normal reference range most commonly used for total bilirubin in adults is about 0.2 to 1.0 mg/dL. This window captures the values seen in healthy individuals; values below 0.2 mg/dL are rare and may result from lab variation, while values above 1.0 mg/dL begin to suggest possible issues with bilirubin production or clearance, though interpretation depends on the fractions (direct vs indirect) and clinical context. The range 0.2–1.0 mg/dL matches the standard total bilirubin reference interval and is the best choice. The other options either shrink the range too much, exclude typical normal values, or state a jaundice threshold rather than a normal reference interval. Jaundice, signaled by higher bilirubin, is commonly around 3 mg/dL or more, but that’s a clinical indicator, not the normal reference range.