Indirect bilirubin, also known as unconjugated bilirubin or free bilirubin, is 80-85% derived from circulating senescent red blood cells, which are lysed in the reticuloendothelial system (spleen, bone marrow, liver) and the released hemoglobin is generated by various enzymes. Another 10-15% of bilirubin is derived from bone marrow and liver, not from senescent red blood cells, mostly ineffective hematopoiesis of bone marrow or from proteins containing hemoglobin in the liver. Knowing its source, we also know the cause of elevated indirect bilirubin, which is mainly due to excessive production of indirect bilirubin bilirubin, which exceeds the liver’s ability to process bilirubin, and a large amount of indirect bilirubin accumulates in the blood, leading to its high value. The causes of excessive bilirubin production are hemolytic and non-hemolytic. A large amount of hemolysis from any clinical cause causes excessive destruction of red blood cells and release of large amounts of hemoglobin, which leads to elevated indirect bilirubin. Non-hemolytic excess bilirubin production is seen in patients with ineffective hematopoiesis that produces too much bilirubin, such as some anemic patients. In addition, impaired uptake and binding of indirect bilirubin by hepatocytes due to various causes of hepatocyte dysfunction can also lead to high indirect bilirubin. Elevated indirect bilirubin can lead to yellow staining of the skin, sclera and mucous membranes, and can be harmful to the nervous system, causing kernicterus through the blood-brain barrier.