Urine Sulfated and Non-Sulfated Bile Acids as a Diagnostic Test for Liver Disease in Cats
To optimize a quantitative colorimetric enzymatic method for measuring urine bile acids (UBA) in cats; 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 79 patients; 65 cats with liver disease and 14 cats with clinical signs overlapping with liver disease but ultimately diagnosed with non-hepatic disorders. Samples from 8 healthy cats 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 were evaluated (in triplicate) for UNSBA and (USBA & UNSBA). Abnormally increased UBAs were 2.0umol/mg Cr for USBA, 1.4 umol/mg Cr for UNSBA, and 4.4 umol/mg Cr for (USBA & UNSBA).
Each UBA test had diagnostic performance similar to the SBA test; the UNSBA test produced equivalent results. Test performance for USBA, UNSBA, USBA & UNSBA, and SBA, respectively were: SP 94, 88, 88, 88; SS: 78, 87, 85, 87; + PV 98, 96, 96, 96; and -PV: 57, 68, 65, and 68. Inter-assay repeatability for UNSBA yielded a 14.5 % CV (n=19; 7 assays) and for UNSBA & USBA 16.7% (n=26; 8 assays). Intra-assay repeatability yielded a 3.4 %CV for UNSBA (n=9), and 12.2 % CV for UNSBA & USBA (n=9). Mean TC recovery was a 109.6 +/- 10.03 % for UNSBA and 83.1 +/- 17.9% for UNSBA & USBA. Significant positive correlations were found between UBA and serum enzymes, total bilirubin, and SBA; p < 0.05).
Seemingly, the UNSBA or the combined USBA & UNSBA tests may be practical diagnostic tests, and perhaps screening tests, to identify hepatobiliary disorders in cats. Since the UBA tests reflect an "average" SBA concentration during the interval of urine formation, these may obviate the influence of the enterohepatic bile acid flux that sometimes confuses SBA interpretation.