Is indirect bilirubin water-soluble?

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Indirect bilirubin, or unconjugated bilirubin, is lipid-soluble and travels in the bloodstream bound to albumin. Because it’s not water-soluble, it cannot be excreted in urine or directly into bile in its circulating form. In the liver, it must be conjugated by UDP-glucuronyl transferase to form direct (conjugated) bilirubin, which is water-soluble. This conjugated form is then excreted into bile and eventually into the intestine; some may appear in urine if there is cholestasis or overflow. So, indirect bilirubin is not water-soluble in its circulating form; only after conjugation does bilirubin become water-soluble.