Values derived from a blood bilirubin test are known as bilirubin levels. Bilirubin is a brownish-yellow substance formed in the liver after it breaks down old red blood cells. It circulates in the bloodstream, and a blood test can be used to determine blood bilirubin levels, according to WebMD.
Bilirubin circulates in the blood in two forms, namely direct and indirect bilirubin, explains WebMD. A bilirubin test is used to derive the levels of both direct and indirect bilirubin levels as well as the total bilirubin level in the blood, states Healthline.
Normal bilirubin test levels are 0.1 to 1 milligrams per deciliter of total bilirubin and 0 to 0.3 milligrams per deciliter for direct bilirubin, notes Mayo Clinic. High bilirubin levels are normal for newborns, and 60 percent of newborns have bilirubin levels of higher than 5 milligrams per deciliter, according to Healthline. Lower than normal bilirubin levels are not usually cause for alarm, but elevated bilirubin levels may indicate liver damage or disease, notes Mayo Clinic.
A bilirubin test is used to determine blockage of liver bile ducts; inspect progression of liver diseases such as hepatitis; detect increased white blood cell breakdown; investigate drug toxicity; and investigate jaundice, which is yellowing of the skin caused by high bilirubin levels, notes Mayo Clinic.