[kjc]

Usually, but not all the time, there is more than one liver enzyme that is elevated in PSS/Liver Shunt. The ALT is... well here it is:


http://veterinarymedicine.dvm360.com/vetmed/article/articleDetail.jsp?id=325515&pageID=1&sk=&date=


Increases in serum liver enzyme activities are sensitive indicators of hepatobiliary disease, but these activities can be elevated secondary to various endocrinopathies, gastrointestinal disease, pancreatic disease, systemic disease, and enzyme induction. In asymptomatic patients, a systematic approach is required to obtain a definitive diagnosis. A careful review of the patient's history is essential to uncover vague clinical signs that the owner may have missed and to identify any potential exposure to hepatotoxic agents. A complete minimum database, including a complete blood count and urinalysis, is required to rule out an underlying extrahepatic disease. In some cases, sequential monitoring may be elected; however, persistent elevation, marked elevations, concurrent increases in serum bilirubin concentrations, or concurrent decreases in albumin concentrations warrant further investigation, including diagnostic imaging and, in many cases, hepatic biopsy.


In patients with portosystemic shunts, twofold to threefold increases in serum ALP, ALT, and AST activities have been recorded while patients with microvascular dysplasia may have normal to mild increases in these enzyme activities.20 Microcytic red blood cells are commonly noted in cases of portosystemic shunts but are not seen in cases of microvascular dysplasia


Increases in serum ALT activity have the highest sensitivity (80% to 100%) for hepatic inflammation and necrosis, vacuolar hepatopathy, and primary neoplasia (hepatocellular carcinoma, cholangiocarcinoma) but have less sensitivity (50% to 60%) in cases of hepatic congestion, metastatic neoplasia, and portosystemic vascular anomalies.3

Best info on LS/PSS: http://www.vet.utk.edu/clinical/sacs/shunt/faq.php