MEASUREMENT OF SERUM BILE-ACIDS CONCENTRATIONS FOR DIAGNOSIS OF HEPATOBILIARY DISEASE IN CATS

Serum bile acid concentrations were measured after food have been withheld for 12 hours (fasting serum bile acid [FSBA] concentration) and 2 hours after a meal (post-prandial serum bile acid [PSBA] concentration) using a direct enzymatic procedure in 108 cats clinically suspected of having hepatobiliary disease. In all cats, liver tissue was examined histologically to confirm the diagnosis. Twenty-six cats did not have histologic evidence of hepatobiliary disease and served as controls. The remaining 82 cats had hepatobiliary disease including hepatic lipidosis (n = 20), portosystemic vascular anomaly (n = 24), hepatic necrosis (n = 13), hepatic neoplasia (n = 8), or cholestatic hepatic disease (n = 17). Sensitivity and specificity of measuring FSBA and PSBA concentrations were calculated for each test alone and when results were interpreted in combination (ie. in series and in parallel), and were compared with sensitivity and specificity of routinely used serum biochemical tests, including measuring serum activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and gamma-glutamyltransferase, and measuring serum concentrations of cholesterol, BUN, and total bilirubin. When tests were considered individually, determination of FSBA and PSBA concentrations had higher specificity than did the other tests (using a cutoff of 15 mu mol/L for FSBA concentration and of 20 mu mol/L for PSBA concentration). Determination of PSBA concentration had the highest sensitivity of all single tests in cats with hepatic lipidosis, portosystemic vascular anomaly, or cholestasis; determination of alanine aminotransferase activity of PSBA concentration had the highest sensitivity for cats with hepatic neoplasia; and determination of aspartate aminotransferase activity had the highest sensitivity for cats with hepatic necrosis. For all cats with hepatobiliary disease, determination of PSBA concentration had the highest sensitivity of any single test. Combination testing using results of measuring total serum bile acid concentrations in conjunction with results of measuring serum enzyme activity or total bilirubin concentration gave the best overall test performance. Results indicate that both the FSBA and PSBA concentration should be determined, but that if paired samples cannot be collected, the PSBA concentration should be preferentially measured. In a small number of cats (6/108), the FSBA concentration exceeded the PSBA concentration.