Significance of serum delta bilirubin during obstructive jaundice in dogs

delta-Bilirubin, a nonenzymatic covalently bound complex with albumin, is nonenzymatically formed in serum and has a long half-life irrespective of hepatorenal function. The aim was to examine if delta-bilirubin reflects the duration of obstructive jaundice and efficacy of biliary drainage.

Obstructive jaundice was developed in 17 dogs either for 4 (short term; n = 9) or 11 (long term; n = 8) days and then external biliary drainage was performed. Serum total, direct, and delta-bilirubin fractions were analyzed by high-performance liquid chromatography.

delta-Bilirubin was not detectable in serum before biliary obstruction. The serum total and direct bilirubin levels increased rapidly and reached a plateau within 2 days after the biliary obstruction, whereas the concentration and proportion of delta-bilirubin gradually increased and significantly correlated with the duration of obstructive jaundice. Before biliary drainage, the proportion of delta-bilirubin was 28.9 +/- 2.4% in the short-term and 42.5 +/- 2.4% in the long-term obstruction group. The decline indices of serum total, direct, and total minus delta-bilirubin in the short-term group (-0.17, -0.19, and -0.26, respectively) were significantly (P < 0.05) greater than those in the long-term obstruction group (-0.10, -0.10, and -0.13). The decline index of delta-bilirubin itself was similar between the groups.

The concentration and proportion of delta-bilirubin in serum reflect the duration of jaundice. Because delta-bilirubin is not excreted into bile and urine and is not toxic to organs, a decline index of total bilirubin minus delta-bilirubin, the excretable bilirubin fraction might be better to assess the efficacy of biliary drainage.