As mentioned, increased thirst in dogs can be a result of increased urination. In this regard, there seems to be a lot of factors that can induce too much urination. Kidney diseases, liver malfunction, diabetes mellitus and the like can lead to polyuria (a term that means an increased frequency or volume of urine outflow). Moreover, Cushing’s disease, hyperparathyroidism and hyperthyroidism can lead to excessive thirst. All of which involves hormonal imbalances that disrupts the normal water balance within the dog’s body. In elderly female canines though, pyometra (a type of infection involving the uterus) can also lead to such. Take note, these are just some of the many conditions that can lead to too much thirsting. There are many other diseases that lead to the same although they are not that common.
If blood tests and urinalysis came back normal, I would be more inclined to look for Cushing’s Disease especially if there are other symptoms which are typical for Cushing’s Disease like a pot belly or symmetrical hair loss; an ultrasound may be unrewarding but may shed some light on other issues within the abdomen. Increased thirst and urination may be caused by many different conditions including other hormonal conditions, infections, age, spinal disorders (more the incontinence) or dietary changes. Regards Dr Callum Turner DVM