Postrenal azotemia results from an obstruction of the urinary outflow tract or discontinuity of the outflow tract with extravasation of urine into body compartments. Prostatic hypertrophy usually does not cause obstruction in the dog. Prostatic abscess or tumor can cause obstruction. If urine can be obtained, the laboratory findings are the same as those of prerenal azotemia. Potassium is commonly elevated as potassium is a small molecule and is reabsorbed from the urine back into blood.
Treatment is to treat the underlying cause.
The prognosis is good if the underlying cause can be treated Postrenal azotemic states can progress to intrinsic renal disease due to increased pressure in the renal tubules or due to hypotension and prerenal influences caused by dehydration. It is important to differentiate acute from chronic renal failure to determine prognosis. ARF has a poor short term prognosis but good long prognosis. CRF has a good short term prognosis but poor long term prognosis.