Bilirubin is a yellow pigment produced when red blood cells break down, measured in blood tests to assess liver function and diagnose conditions like jaundice.
Red blood cells live about 120 days before breaking down in the spleen. Hemoglobin inside these cells releases iron, which the body reuses, and heme, which converts into bilirubin. This process happens continuously, producing about 250-300 mg of bilirubin daily.
Bilirubin travels through the bloodstream to the liver, where it combines with glucose molecules to form bilirubin glucuronide. The liver then excretes this compound into bile, which aids digestion. Finally, the intestines eliminate bilirubin through stool, giving it its characteristic brown color.
| Type | Source | Normal Range (mg/dL) |
|---|---|---|
| Unconjugated (indirect) bilirubin | Breakdown of hemoglobin | 0.1-0.8 |
| Conjugated (direct) bilirubin | Processed by the liver | 0-0.3 |
| Total bilirubin | Sum of both types | 0.3-1.2 |
Laboratories measure these types separately to diagnose liver diseases. Unconjugated bilirubin is insoluble in water, while conjugated bilirubin is water-soluble.
Elevated bilirubin levels indicate liver dysfunction or other conditions. Jaundice, a yellowing of skin and eyes, occurs when bilirubin levels exceed 2.5-3.0 mg/dL. Causes include:
Doctors use bilirubin tests alongside other liver function tests to diagnose and monitor these conditions. For example, a patient with jaundice and high unconjugated bilirubin may have Gilbert's syndrome, while high conjugated bilirubin suggests liver disease or bile duct obstruction.
Many people confuse bilirubin with other liver-related substances or assume high levels always indicate severe disease. However, mild elevations often occur temporarily due to stress, dehydration, or fasting., newborns naturally have higher bilirubin levels, leading to neonatal jaundice, which usually resolves without treatment.
Another misconception is that bilirubin only indicates liver problems. While it primarily reflects liver function, elevated levels can also result from excessive red blood cell breakdown, as seen in hemolytic anemia.
During a routine checkup, a 35-year-old patient showed mild jaundice and fatigue. Blood tests revealed elevated unconjugated bilirubin but normal liver enzymes. Further testing confirmed Gilbert's syndrome, a harmless genetic condition causing intermittent bilirubin spikes. The patient required no treatment but learned to manage stress and hydration to minimize symptoms.