Serum bilirubin is a yellow compound that occurs in the normal catabolic pathway that breaks down heme in red blood cells. The normal range for serum bilirubin varies slightly among different laboratories but is generally considered to be between 0.1 and 1.2 milligrams per deciliter (mg/dL) or 1.7 to 20.5 micromoles per liter (μmol/L) for adults. Bilirubin levels are an important indicator of liver function and hemolysis (the breaking down of red blood cells), and abnormal levels can suggest various health issues.
Understanding Serum Bilirubin
Serum bilirubin is categorized into two main types: direct (conjugated) bilirubin and indirect (unconjugated) bilirubin. Direct bilirubin is water-soluble and occurs after bilirubin has been processed in the liver, where it is conjugated with glucuronic acid. Indirect bilirubin is not water-soluble and represents the form of bilirubin before it is processed by the liver. Normally, the total bilirubin level (which is the sum of direct and indirect bilirubin) is less than 1.2 mg/dL, with the direct fraction usually being less than 0.3 mg/dL.
Normal Ranges by Age
The normal ranges for serum bilirubin can vary slightly depending on the age of the individual. For newborns, especially in the first week of life, bilirubin levels can be higher due to the breakdown of red blood cells and the liver’s initial inability to process all the bilirubin being produced. This condition, known as neonatal jaundice, typically resolves on its own but can sometimes require treatment to prevent kernicterus, a type of brain damage caused by high bilirubin levels.
| Age Group | Normal Range (mg/dL) |
|---|---|
| Newborns (0-1 week) | Up to 15 mg/dL (physiologic jaundice) |
| Infants (1-2 weeks) | Less than 5 mg/dL |
| Adults | 0.1-1.2 mg/dL |
Interpretation of Bilirubin Levels
Abnormal bilirubin levels can indicate a variety of conditions. Elevated levels of indirect bilirubin may suggest hemolysis, while elevated direct bilirubin levels can indicate issues with bile ducts, such as obstruction, or problems with the liver, such as hepatitis or cirrhosis. Certain medications and conditions can also affect bilirubin levels.
Clinical Significance
The clinical significance of bilirubin levels extends beyond diagnosing liver and hemolytic disorders. High levels of bilirubin, particularly in newborns, can lead to serious complications if not managed properly. In adults, chronic elevations can be a sign of underlying liver disease or other conditions requiring medical attention.
Elevated bilirubin levels can be a sign of serious health issues and require prompt medical evaluation. Hemolysis, or the breakdown of red blood cells, can lead to increased levels of indirect bilirubin. On the other hand, direct bilirubin elevations often indicate problems with the liver or bile ducts, such as cholestasis, where bile flow is reduced or blocked.
What is the normal range for serum bilirubin in adults?
+The normal range for serum bilirubin in adults is generally considered to be between 0.1 and 1.2 mg/dL.
What does an elevated bilirubin level indicate?
+An elevated bilirubin level can indicate a variety of conditions, including hemolysis, liver disease, or bile duct obstruction, depending on whether the elevation is in direct (conjugated) or indirect (unconjugated) bilirubin.
How is bilirubin level measured?
+Bilirubin levels are measured through a blood test, where a sample of blood is drawn from a vein and sent to a laboratory for analysis.
