What is indirect bilirubin?

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Indirect bilirubin is the unconjugated form. It comes from the breakdown of heme and travels in the blood bound to albumin, so it isn’t water-soluble and isn’t excreted in urine yet. The liver then takes it up and conjugates it with glucuronic acid to form a direct (conjugated) bilirubin, such as bilirubin diglucuronide, which is water-soluble and excreted into bile. So, the term indirect bilirubin specifically refers to the unconjugated, not-yet-conjugated form.