Liver function in cats with hyperthyroidism before and after 131I therapy

Background: The clinical significance of high serum concentration or activity of markers of liver damage in cats with hyperthyroidism is unknown. Objective: To evaluate serum markers of liver function and damage, and ultrasonographic changes in cats with hyperthyroidism and with high liver enzymes, and to determine if abnormalities resolve after treatment with I'll. Animals: Nineteen cats with hyperthyroidism (15 with high serum activities of liver enzymes) and 4 age-matched healthy control cats. Methods: Serum bile acids, albumin, ammonia, cholesterol, and blood urea nitrogen concentrations, and activities of liver-derived enzymes, and blood glucose concentrations were measured before and after I-131 therapy. These values were compared with those of cats that were euthyroid. In addition, gross liver parenchymal changes detected by abdominal ultrasonographic examination, before and after I-131 therapy were evaluated. Results: High serum liver enzyme activities were not associated with abnormalities in hepatic parenchyma and liver functional variables, regardless of the degree of increase. Serum liver enzyme activities return to normal after control of hyperthyroidism with I-131 therapy. Cats with hyperthyroidism have a significantly higher serum fasting ammonia concentration than cats who were euthyroid (P =.019). Cats with hyperthyroidism also have significantly lower serum cholesterol (P = .005) and glucose (P = .002) concentrations before compared with after I-131 therapy. Nine of 19 cats with hyperthyroidism had trace ketonuria. Conclusions and Clinical Importance: These results demonstrate that extensive examination for hepatobiliary disease in most cats with hyperthyroidism is unnecessary.