Practical Matters: Desmopressin is safer than water deprivation to identify the cause of polyuria and polydipsia in dogs
Jun 01, 2009
Measuring the basal serum cortisol concentration may help rule out hypoadrenocorticism since this disorder is unlikely if the value is > 2 μg/dl (~70 mmol/L). If the value is ≤ 2 μg/dl, hypoadrenocorticism must be confirmed with an ACTH stimulation test. If hyperadrenocorticism is suspected, perform ACTH stimulation and low-dose dexamethasone suppression tests, imaging, and other diagnostic tests as needed.
To conduct this trial, the owner measures the patient's free-choice 24-hour water intake for two or three days and collects and labels daily urine samples. The specific gravity of the urine samples should be checked. The owner then administers 0.05 to 0.2 mg desmopressin orally every eight hours or 1 to 4 drops of the 100 μg/ml desmopressin nasal spray in one conjunctival sac every 12 hours for five to seven days. The owner monitors the dog's water consumption and collects and labels urine samples during the treatment period. Dogs with central diabetes insipidus should respond well to this treatment, forming more concentrated urine and drinking much less water than they were previously drinking. A moderate response may occur in dogs with partial central diabetes insipidus or with hyperadrenocorticism.
Even with a desmopressin trial, caution should be exercised in geriatric patients and those having isosthenuria since these patients are more likely to have early-stage chronic kidney disease, and excessive dehydration could be damaging. Further, if an animal with unexplained polyuria and polydipsia presents to the hospital in a dehydrated state and its urine specific gravity is < 1.030, a water deprivation test is unnecessary and is contraindicated.
1. Feldman EC, Nelson RW. Water metabolism and diabetes insipidus. In: Canine and feline endocrinology and reproduction. 3rd ed. St Louis, Mo: Saunders, 2004;2-44.
Marjorie L. Chandler, DVM, MS, MACVSc, DACVN, DACVIM, DECVIM, MRCVS