Hyposthenuria in dogs is defined as a urine specific gravity (USG) < 1.008 and urine Osmolality <300 mOsm/kg.
Hyposthenuria implies urine with an osmolality less than that of plasma and indicates decreased reabsorption of water by the kidneys and a normal renal ability to dilute urine.
Urine concentration is determined by the action of vasopressin upon the principal cells of the cortical and medullary collecting ducts, and is dependent upon the presence of a hyperosmotic medullary interstitium.
Hyposthenuria is commonly associated with polyuria, which has many causes.
Correction of hyposthenuria results in isosthenuria.