Serum bilirubin pigments covalently linked to albumin.

The serum levels of biliprotein (i.e., the bilirubin fraction covalently linked to albumin) were measured in patients with hepatobiliary disease by two analytical procedures: reverse-phase anion-exchange chromatography (Bond-Elut) and anion-exchange chromatography. Bond-Elut extracts contained tetrapyrroles, allowing the analysis of biliprotein, bilirubin, and bilirubin conjugates, whereas the anion-exchange method converted tetrapyrroles to azodipyrroles (protein-free), which were adsorbed on the resin, with the exception of azopyrrole of biliprotein (covalently linked to albumin), which passed through the resin and could be analyzed. In contrast, other cationic polymer columns did not completely bind the alkaline diazo derivatives of unconjugated bilirubin, conjugated bilirubin, or the azopyrrole of biliprotein not bound to albumin. Therefore, a comparison was made of these two methods using the original anion-exchange resin. Both procedures gave similar values for serum levels of biliprotein in patients with high levels of total bilirubin.