At least four bilirubin fractions can be separated and identified by liquid chromatography, the least understood being the "delta" fraction (B delta), which apparently is covalently bound to albumin. To learn more about the incidence and significance of B delta, we assayed serum from 539 infants and children, both by the chromatographic method and the routine colorimetric Jendrassik-Grof method. The proportion of B delta appeared to correlate with both age and disease course. For infants younger than 28 days B delta generally was less than 2% of total bilirubin; for hyperbilirubinemic older infants and children the median B delta value was 35%. High B delta (greater than 50% of total bilirubin) in newborns was associated with intra- and extra-hepatic cholestasis, biliary cirrhosis, biliary atresia, and hepatitis. Among older infants and children, a proportion of low B delta (less than 10%) was found in hemolytic anemias, sepsis, shock, and other non-hepatic jaundice. In several cases, when low B delta was accompanied by increased conjugated bilirubin, the prognosis was very poor. Delayed clearance of B delta from the circulation together with its reactivity in direct diazo methods may interfere with interpretation of values for conjugated bilirubin as measured by classical methods.

The absence of hyperbilirubinemia can lead to decreased suspicion of biliary rupture in dogs. This delay of suspicion and treatment can result in increased mortality rates. The objective of this retrospective, observational study was to describe ultrasound and serum bilirubin findings in a group of dogs with an ultrasonographic diagnosis of suspected biliary rupture. The records of a single institution were searched over the period of 2007‐2019 for cases having ultrasound reports describing suspicion of biliary rupture. Clinical findings for each of the cases were recorded. A total of 35 dogs met inclusion criteria and, of these, 30 dogs had confirmed ruptured biliary tracts. It was found that 40% (12/30) of dogs with confirmed ruptured biliary tracts had a serum bilirubin values within the normal reference range. No statistical difference was found in serum bilirubin values between the ruptured and nonruptured biliary tracts. Leukocytosis and neutrophilia were found to be statistically significant between ruptured and nonruptured biliary tracts. Mucinous material, similar to “white bile” found in human literature, was found within the peritoneal effusion of six dogs with biliary rupture, three of which also lacked bile pigment. Findings from this study indicated that normobilirubinemia may be present in some dogs with biliary rupture, and therefore should not be used as a reason for excluding this differential diagnosis.