Thyroid Hormone Concentrations in Dogs With Chronic Weight Loss, With Special Reference to Cancer Cachexia

Serum concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3), free thyroxine (fT4), and free 3,5,3'-triiodothyronine (fT3) were compared between tumor-bearing dogs (with and without chronic weight loss) and non—tumor-bearing dogs (with and without chronic weight loss) (n = 83). Serum T4, T3, and fT3 concentrations were lower (P < .05) in dogs with weight loss, whether or not they were tumor-bearing, than in dogs without weight loss. Serum fT4 concentrations did not vary among the groups. Serum albumin concentrations were lower (P < .05) in cachectic dogs than in dogs not experiencing weight loss, regardless of their tumor-bearing status. Percentage of weight loss was found to be associated (P < .05) with T4, T3, and fT3 concentrations. It appears that the low thyroid hormone concentrations are related to either an abnormal nutritional state or to the severity of illness, rather than to a tumor-related phenomenon.