Diagnostic and predictive ability of hyperbilirubinemia severity in cats: A multicenter retrospective study

Abstract Background Total serum bilirubin concentration (TBIL) can provide useful information on several pathophysiological conditions in cats. Nevertheless, whether the variable severity classification of hyperbilirubinemia can reliably indicate certain disease processes or predict a biliary obstruction (BO) has not been investigated. Hypothesis/Objective Determine if hyperbilirubinemia of variable severity can assist clinicians to identify BO, which often is considered a surgical emergency. Animals Two‐hundred sixteen client‐owned cats. Methods Data were retrospectively collected from all cats (January 2015‐August 2022) with an increased TBIL (>0.58 mg/dL [>10 μmol/L]) presented to 3 referral centers in the United Kingdom (UK). Presenting clinical features and diagnostic outcomes were collected. The predictive ability of TBIL to indicate BO was evaluated by multivariable binary logistic regression modeling and receiver operating characteristic (ROC) curves. Results Median TBIL was 1.73 mg/dL (range, 0.59‐26.15; 29.5 μmol/L; range, 10.1‐447.1) with severity classification of hyperbilirubinemia categorized as mild (>0.58‐2.92 mg/dL; >10‐50 μmol/L; 68.1%), moderate (>2.92‐5.85 mg/dL; >50‐100 μmol/L; 17.6%), severe (>5.85‐11.70 mg/dL; >100‐200 μmol/L; 9.7%) and very severe (>11.70 mg/dL; >200 μmol/L; 4.6%). Biliary obstruction was present in 17 (7.9%) cats, all of which received recommendation for emergency surgery. Median TBIL in cats with BO (9.69 mg/dL; 165.7 μmol/L) differed significantly from those without obstruction (1.51 mg/dL; 25.8 μmol/L; P < .01). The optimal TBIL cut‐off to discriminate between cats with and without BO was ≥3.86 mg/dL (≥66 μmol/L) with a sensitivity of 94.1% and specificity of 82.4%. Using multivariable logistic regression, as age increased, the odds of BO increased significantly (odds ratio, 1.20; 95% confidence interval, 1.01‐1.42; P = .04). Conclusions and Clinical Importance As part of a thorough clinical assessment, the severity classification of hyperbilirubinemia has the potential to predict the likelihood of a BO and to discriminate between cats that may or may not require surgery for BO at a suggested cut‐off of ≥3.86 mg/dL (≥66 μmol/L). Alongside TBIL, age is also useful when assessing for the likelihood of BO in a cat presented with hyperbilirubinemia.