What is the current approach to diagnosing and managing portosystemic shunts in dogs?

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Congenital portosystemic shunt (CPSS) diagnosis begins with liver function tests, with paired serum bile acids (SBA) as the best test to exclude the diagnosis and fasting ammonia (FA) as the best combined screening test. FA has a sensitivity of 77.4% and specificity of 93.3% for diagnosing CPSS, while paired SBA achieves 100% sensitivity and 100% negative predictive value, making a normal paired SBA result sufficient to rule out CPSS in a suspected case.4 Abdominal ultrasound (aUS) has a sensitivity of 80.8% and specificity of 90.0%, but fails to visualize the shunt in approximately 20% of cases and is particularly unreliable for extrahepatic shunts not inserting into the prehepatic caudal vena cava.4 When clinical suspicion remains after initial bloodwork, advanced imaging is required for anatomic confirmation and surgical planning. Computed tomography angiography (CTA) has a sensitivity of 96% and specificity of 89% for detection of extrahepatic PSS.7 Portography remains the gold standard for portal system visualization but is being replaced by CTA, MRI, and ultrasonography in most centers.7 Nuclear scintigraphy, ultrasound, CT, and MRI are all accepted modalities for confirming intrahepatic portosystemic shunt (IHPSS) diagnosis and classifying shunts as left, right, or central divisional.5 A machine learning model using routine CBC and chemistry data achieves a sensitivity of 94.3% and specificity of 90.5% for diagnosing any PSS, with mean corpuscular hemoglobin, lymphocyte count, and serum globulin concentration as the most predictive variables.2 This tool is best used as a pre-imaging screening step to raise or lower index of suspicion before committing to advanced imaging.2 Shunt morphology influences clinical presentation and should guide diagnostic suspicion. Dogs with portocaval (PC) shunts present significantly younger, with lower body condition scores, more severe clinical signs, more pronounced microcytosis and monocytosis, lower urea and creatinine, and