Urine Sulfated and Non-Sulfated Bile Acids as a Diagnostic Test for Liver Disease in Dogs
To optimize a quantitative colorimetric enzymatic method for measuring urine bile acids (UBA) in dogs; to examine the clinical utility of UBA measurements for diagnosis of hepatobiliary disease; to compare test performance with the serum bile acid (SBA) test (specificity (SP), sensitivity (SS), and predictive values (PV)); and to calculate correlation coefficients with conventionally used tests.
Routine serum biochemistries, SBA, and urine samples were collected from 130 patients; 107 dogs with liver disease and 23 dogs with clinical signs overlapping with liver disease but ultimately diagnosed with non-hepatic disorders. Samples from 15 healthy dogs established a normal UBA range. All specimens in an individual were collected within 48 hours. UBA values were normalized using urine creatinine (Cr). Three different UBA methods were investigated: 1)urine sulfated bile acids (USBA), 2)urine non-sulfated bile acids (UNSBA), and 3)combined USBA & UNSBA. Inter- and intra-assay repeatability and recovery of bile acids (40 and 100 umol taurocholate (TC))added to urine (in triplicate)were evaluated. Abnormally increased UBAs were 0.9 umol/mg Cr for USBA, 6.8 umol/mg Cr for UNSBA, and 7.3 umol/mg Cr for (USBA & UNSBA).
UNSBA and USBA & UNSBA tests gave the best diagnostic performance of the UBA tests; the combined test outperforming SBAs in SP and +PV. Test performance for USBA, UNSBA, USBA & UNSBA, and SBA, respectively were: SP: 87, 91, 91, and 65; SS: 15, 61, 58, and 78; + PV: 84, 97, 97, and 91; and -PV: 18, 33, 32, and 39. Inter-assay repeatability for UNSBA yielded a 9.9 % CV (n=34, 8 assays) and for UNSBA & USBA a 12.0 % CV (n=26, 8 assays). Intra-assay repeatability yielded a 5.4% CV for UNSBA (n=8), and 8.1% CV for UNSBA & USBA (n=9). Mean TC recovery was 113 +/- 24 % for UNSBA and 101.6 +/- 17.7 % for UNSBA & USBA. Correlations with routine tests, except SBA (significantly positive), were variable.
The combined UNSBA & USBA test offers an accurate and reproducible alternative for detecting abnormally increased SBA values. This test seemingly may obviate changes relating to the dynamics of the enterohepatic bile acid flux that can sometimes confuse interpretation of SBA values in patients with important liver disease.