Canine Population
Increased alkaline phosphatase (ALP) was seen in 15 (17%) dogs. Of these dogs, 4 had concurrent increases in their urine cortisol:creatinine ratios (UCCR), suggesting the possibility of hyperadrenocorticism. Three of four dogs were worked up further. Dexamethasone suppression tests were run on these patients and results indicated the presence of pituitary-dependent hyperadrenocorticism.

The UCCR was elevated in 14 dogs (16%). In 26 (29%) dogs, total T4 values were below normal. Eleven were reevaluated and nine dogs were diagnosed with hypothyroidism based on low free T4 (ED) values.

Eleven (11%) of the dogs had bacteriuria and pyuria. Four of them were also found to be azotemic, in the absence of clinical dehydration, consistent with possible pyelonephritis. Urine specific gravity of 2 of these dogs were 1.026 and 1.015, and both had positive urine cultures. This highlights the importance of performing a routine urinalysis, preferably on urine collected by cystocentesis, as part of the routine health assessment.

Feline Population
Elevations in the total T4 were noted in 6 (16%) of 100 cats. However, thyroid nodules were palpable on physical examination in only 1 of them.

Nine cats were found to be azotemic based on elevations in BUN and creatinine in the absence of clinical dehydration. Five of them had urine specific gravity below 1.035.

One of the 100 cats was diagnosed with diabetes mellitus based on persistent hyperglycemia and glucosuria.

Canine Population
Elevations in serum ALP can be due to a variety of factors, including bone disease, cholestasis, drug induction, neoplasia, hepatic nodular hyperplasia, hepatitis, reactive hepatopathy, and endocrine disease. The absence of medications known to alter ALP makes exogenous induction unlikely to be the cause of high ALP in these dogs. In this study, three dogs were diagnosed with hyperadrenocorticism and the disease was suspected in one other due to an increase in ALP and elevated UCCR. The only clinical sign noted by the owner of one dog diagnosed with hyperadrenocorticism was recent weight gain.

Of the 90 dogs studied, 14 (16%) had elevated UCCR. There was no evidence in these dogs of non-adrenal illness based on other laboratory tests or clinical examination findings. Previous studies have demonstrated a relationship between dogs that develop geriatric-onset behavioral changes and elevations in UCCR values. This is thought to be due to dysregulation of the hypothalmic-pituitary-adrenal axis seen in geriatric dogs which develop Alzheimer-like behavioral changes in the absence of an underlying medical condition.

Hypothyroidism is one of the most common endocrinopathies diagnosed in the dog. Typically, hypothyroidism affects dogs between the ages of 4 and 10 years with spayed females and castrated males being at an increased risk. Of the 90 older dogs studied, 26 (20%) had decreased total T4 concentrations. However, this parameter can be affected by other nonthyroidal illnesses making it unreliable by itself in diagnosing hypothyroidism. Eleven of these dogs were reevaluated by measuring free T4 (ED) concentrations; five of them were decreased, thus confirming hypothyroidism. None of these dogs was displaying classic symptoms of hypothyroidism.

Feline Population
Hyperthyroidism was diagnosed in 6 of the 100 cats based on elevated total T4 concentrations. While this condition is still the most common endocrine disorder diagnosed in the cat, increased awareness of the problem has resulted in earlier detection and intervention before the onset of severe signs. Only one of the cats diagnosed with hyperthyroidism in this study was symptomatic based on the owner’s observations. Feline hyperthyroidism is typically caused by thyroid adenomas with the age of onset ranging from 4 to 22 years. About 6% of hyperthyroid cats are less than 10 years of age at the time of diagnosis, although 3 of the 6 hyperthyroid catsstudied here were under 10 years of age.

Nine of the 100 cats had azotemia and 5 of these 9 cats had renal failure based on a urine specific gravity < 1.035.

As pets age, the importance of routine veterinary visits and diagnostic laboratory screening becomes even greater. The overall prevalence of disease found in these apparently healthy dogs and cats was one of the most valuable findings in the study. Despite the fact that these animals were not being treated for any underlying medical problems, clinically significant disease was found in more than 20% of the canine population and more than 17% of the feline population.

Subclinical disease is thus relatively common in the senior dog and cat. Veterinarians should therefore consider spending more time taking a thorough history, and performing physical examinations and laboratory tests with geriatric animals. As many owners may dismiss early clinical signs of illness as "simple aging" and not mention them to the veterinarians, we should rely less on the owner to provide information about changes in their pet’s physical and behavioral health since the last office visit. Scheduling frequent follow-up visits can also help detect early signs of an emerging health problem.