Introduction
Bilirubin metabolism is a key indicator of liver function. In acute hepatitis, bilirubin levels can be significantly elevated due to hepatocellular injury. Among the different fractions of bilirubin, delta bilirubin (δ-bilirubin) plays a unique role, particularly in assessing jaundice resolution.
What is Delta Bilirubin?
Delta bilirubin is a covalently albumin-bound form of bilirubin that is formed when direct (conjugated) bilirubin irreversibly binds to albumin in circulation. Since albumin has a half-life of about 14–21 days, delta bilirubin remains in the blood for a longer period compared to unconjugated or free conjugated bilirubin.
Delta Bilirubin in Acute Hepatitis
In acute hepatitis, hepatocellular damage leads to:
- Impaired conjugation and excretion of bilirubin, causing increased direct (conjugated) bilirubin in the blood.
- Leakage of conjugated bilirubin into circulation, where it binds to albumin, forming delta bilirubin.
- Prolonged jaundice, as delta bilirubin persists even after the liver starts recovering and bilirubin excretion improves.
Clinical Importance of Delta Bilirubin
- Prolonged Jaundice:
- After acute hepatitis subsides, total bilirubin may remain elevated due to delta bilirubin, even when liver function is improving.
- This explains why jaundice may persist for weeks after other liver enzymes normalize.
- Interpreting Liver Function Tests (LFTs):
- If direct bilirubin remains elevated, check for delta bilirubin to avoid unnecessary investigations for obstructive jaundice.
- A high delta bilirubin fraction suggests post-hepatitis jaundice rather than an ongoing liver insult.
- Differentiation from Cholestasis:
- In cholestatic liver diseases, direct bilirubin remains high due to ongoing obstruction.
- In acute hepatitis, high bilirubin may be due to delta bilirubin, indicating prior hepatocellular injury rather than ongoing bile duct obstruction.
Key Takeaways
- Delta bilirubin is a conjugated bilirubin fraction bound to albumin.
- It has a prolonged half-life (~14–21 days), leading to persistent jaundice post-hepatitis.
- Recognizing delta bilirubin helps avoid unnecessary investigations for prolonged jaundice.
- It is significant in differentiating post-hepatitis jaundice from cholestasis.
