According to PetMD, common signs of kidney failure in dogs include depression, lethargy, lack of appetite, vomiting, diarrhea, constipation and weight loss. Other symptoms include increased thirst, increased volume of urination, increased frequency of urination, blood in the urine, blindness, seizures and comas. The onset of these symptoms may occur gradually, and not all dogs experience all of these symptoms. Indicators of failure are found in urine and blood tests.
PetMD notes that several indicators of chronic renal failure are often observed by the veterinarian upon examination of the dog and are often present in the dog's blood tests and urinalysis. Elevated blood pressure in a dog is an indication of kidney problems since kidneys regulate blood pressure. Blood tests that reveal the dog has anemia may indicate kidney issues. Indicators found during urinalysis of the dog's urine include abnormal electrolyte levels, elevated levels of protein enzymes, such as creatinine and high blood urea nitrogen.
If the urine is neither concentrated nor dilute, then the kidneys are not processing urine correctly and likely are failing. Since kidney failure often causes kidneys to shrink, observation via X-ray or ultrasound imaging that the dog's kidneys are abnormally small may point to kidney failure, according to PetMD.