Oliguria or hypouresis is the low output of urine specifically more than 80 ml/day but less than 400ml/day.^[1] The decreased output of urine may be a sign of dehydration, kidney failure, hypovolemic shock, hyperosmolar hyperglycemic nonketotic syndrome (HHNS), multiple organ dysfunction syndrome, urinary obstruction/urinary retention, diabetic ketoacidosis (DKA), pre-eclampsia, and urinary tract infections, among other conditions.

This article or section appears to contradict itself on threshold for daily urine output qualifying as oliguria (variously given as 80-100mL/<400mL/<500mL in intro/Definition section). (May 2021)

Beyond oliguria is anuria, which represents an absence of urine, clinically classified as below 80 or 100 ml/day.^[1]

The term oliguria is derived from oligo-meaning "small, little," + -uria, from the Greek word ouron, meaning "urine".^[2]

Oliguria is defined as a urine output that is less than 1 mL/kg/h in infants,^[3] less than 0.5 mL/kg/h in children,^[3] and less than 400 mL^[3] or 500 mL^[4] per 24h in adults - this equals 17 or 21 mL/hour. For example, in an adult weighing 70 kg it equals 0.24 or 0.3 mL/kg/h. Alternatively, however, the value of 0.5 mL/kg/h is commonly used to define oliguria in adults as well.^[4]

Perform ultrasound examination of the kidney to rule out obstructive processes.^{[citation needed]}

The mechanisms causing oliguria can be categorized globally in three different categories:^{[citation needed]}

• Prerenal: in response to hypoperfusion of the kidney (e.g. as a result of dehydration by poor oral intake, cardiogenic shock, diarrhea, G6PD deficiency, massive bleeding or sepsis)
• Renal: due to kidney damage (severe hypoperfusion, rhabdomyolysis, medication)
• Postrenal: as a consequence of obstruction of the urine flow (e.g. enlarged prostate, tumour compression urinary outflow, expanding hematoma or fluid collection)

Oliguria, when defined as less than 1 mL/kg/h, in infants is not attributed to kidney failure.^[5]

• Polyuria (excessive urine production)
• Anuria (absolute lack of urine output)
• Intraabdonmial hypertension (IAH) and Abdominal Compartment Syndrome (ACS)