Like all cells in the human body, red blood cells experience a life cycle of creation, maturation, and then destruction. When a red blood cell has reached the end of its life, it is broken down into its base component—one of which is bilirubin, a yellow pigment. The bilirubin will then circulate through the blood on its way to the liver where it will be excreted into the bile duct and stored in our gall bladder. Eventually, it will be released into the small intestine to aid in the digestion of fats and ultimately is excreted in stool. There are two forms of bilirubin that can be measured by a blood test: conjugated (direct) and unconjugated (indirect). All of the bilirubin in our body together is called “total” bilirubin. “Direct” or “conjugated” bilirubin indicates that a sugar has been attached to it. “Indirect” or “unconjugated” bilirubin indicates the absence of a sugar. The important distinction is that direct bilirubin is water soluble, while indirect bilirubin is not. Blood tests to assess bilirubin will measure total, direct, and indirect. Comparing the three results will provide information regarding the condition that may be present, including: damage to the liver, liver disease, jaundice (yellowing of the skin / eyes), and cancer of the gallbladder or pancreas. 

Normal ranges in mg/dL:

 0-1 days:    2.0-6.0 
 2-5 days:   6.0-10.0 
 6-30 days: 4.0-8.0 
 >30 days:  0.3-1.2