Clinically Oliguria is defined as less than 400ml urine within 24 hours or less than 17 ml urine per hour; while less than 100ml urine is referred to as Anuria. Patients with Oliguria and Anuria often suffer increasing creatinine and urea nitrogen, electrolyte balance out of order, and metabolic acidosis, etc. Clinically there are three common reasons which can lead to Oliguria or Anuria:
The first one is prerenal factor. The decrease of effective circulating blood in the whole body leads the renal blood flow to drop and it can also lead glomerular filtration pressure and filtration rate to descend, all of which cause urine volume to decline. This phenomenon is often seen in dehydration, heart failure, shock, hypotension, thrombosis of the renal artery, etc.
The second one is renal factors. Renal parenchymal damage leads to Oliguria and Anuria, which are found in acute nephritis, acute progressive nephritis, acute interstitial nephritis, acute tubular necrosis, and renal failure which is cause by various chronic glomerulonephritis.
The last one is post-renal factor. It is mainly caused by urinary tract obstruction, and is often due to renal pelvis stone, ureteral calculus, lump obstruction in ureter, Ureteral inflammation, edema, stenosis, or obstruction caused by oppression adhesion from outside kidneys.