Source:http://linkedlifedata.com/resource/umls/id/C1881193
NCI: Bilirubin is in the insoluble form, unconjugated bilirubin (indirect bilirubin).The non-water soluble, free bilirubin does not react with sulfanilic acid at acidic pH to produce a red colored complex until an accelearator, alcohol, is added to the solution to perform a quantitative measurement of unconjugated bilirubin levels.,NCI: A measurement of the unconjugated or non-water-soluble bilirubin in a biological specimen.