Bile Acids, Direct Bilirubin and Gamma-glutamyltransferase as Prognostic Indicators for Horses with Liver Disease in the Eastern United States: 82 Cases (1997-2019).

This research article presents the results of a study evaluating the use of certain biochemical tests and liver biopsies as prognostic indicators in horses with liver dysfunction. The study found that the level of direct bilirubin was the most effective predictor of survival, while other commonly used indicators, such as bile acids, gamma-glutamyltransferase and presence of fibrosis, were not associated with outcome.

Objective and Methodology

• The study was a retrospective multicenter analysis that aimed to assess how effective three specific liver biochemical tests and liver biopsies were in predicting the prognosis of horses with liver dysfunction.
• The biochemical tests evaluated were for bile acids (BA), direct bilirubin and gamma-glutamyltransferase (GGT).
• The study included 82 horses, over one year old, which were examined at four referral hospitals in the eastern United States.
• These horses had bile acid (BA) values greater than 30 µmol/L and had been followed up for at least six months after the testing.
• The researchers used logistic regression analysis to evaluate the association between the maximum values of BA, GGT and direct bilirubin from each horse and the horse’s survival.
• They also used a chi-square test to compare the presence or absence of fibrosis (as reported in liver biopsies) between surviving and non-surviving horses.

Findings

• The study found that the degree of increase in BA concentration and GGT activity was not related to outcome.
• Similarly, the presence of fibrosis in the liver, observed through biopsies, was also not associated with the horse’s survival.
• However, elevated direct bilirubin concentration was positively associated with non-survival. This suggests that direct bilirubin values can be used as a reliable prognostic indicator for horses with liver dysfunction.

Implications

• The findings suggest that GGT and BA values, as well as the mere presence of fibrosis on liver histopathology, should not be taken as prognostic indicators in such cases.
• This contradicts common practice where these values and observations are frequently used in prognosis.
• On the contrary, direct bilirubin values were found to be a good predictor of outcome, pointing towards a shift in veterinary diagnostic practices for horses with liver dysfunction.