Oliguria is the term used when there is an abnormally low production of urine by the body. Anuria, on the other hand, is no production of urine at all.
A helthy dog produces one to two ml of urine per kg of body weight per hour. In oliguria, the urine production rate decreases to less than 0.25 ml/kg/hour while in anuria, the production rate is less than 0.08 ml/kg/hour.
Low urine production rate or oliguria can be caused by physiologic or pathologic condition. Physiologic condition is when kidneys produce less urine in order to preserve body fluids and electrolyte balance. This occurs in response to high plasma osmolality or low effective circulating fluid volume which increase antidiuretic hormone (ADH) synthesis and its release. ADH acts on the kidneys to induce formation of small quantities of concentrated urine.
Pathologic oliguria occurs due to kidney damage.
Anuria or no urine formation is often associated with acute kidney failure or obstruction in urinary flow as well as rupture of the urinary excretory pathway
Besides abnormally low production urine production or essentially no urine formation, other symptoms depend upon type of oliguria or anuria (whether physiologic or pathologic). Dehydration, pale mucous membrane, a weak pulse, a rapid or irregular pulse, and a history of fluid loss (through excessive vomiting or diarrhea, for example) are signs of physiologic oliguria. Pathologic oliguria signs include a history of progressive kidney disease with symptoms such as poor appetite and weight loss.
In dogs with anuria, physical examination may reveal fluid infiltration into the tissues surrounding the urinary tract, and pain in the abdomen on palpation.