Urinoutput

Urinoutput, commonly referred to as urine output, is the volume of urine produced by the kidneys over a given period. It is routinely measured to assess fluid balance and kidney function. In clinical contexts, urine output is often recorded hourly to monitor rapidly changing conditions.

In adults, normal urine output is commonly cited as about 0.5 mL per kilogram of body weight per hour, roughly 800–2,000 mL per day for a typical adult with normal fluid intake. A minimum adequate output is often taken as 0.5 mL/kg/h. Per the same framework, pediatric values differ and are generally higher on a per-kilogram basis.

Oliguria describes urine output below 0.5 mL/kg/h for several hours; anuria refers to urine output less than 100 mL in 24 hours. Polyuria indicates abnormally high output, often defined as more than about 2.5–3 liters per day. These patterns help distinguish hydration status, kidney function, and potential pathology.

Urine output can be measured by timed urine collection or by using a urinary catheter with a collection device in hospital, or by measuring the volume in a urine bag after specified intervals. In ambulatory care, patient-reported output is less precise and may be supplemented by intake-output charts.

Clinical significance and monitoring: urine output is a key indicator of renal perfusion and kidney function and can reflect hydration status, diuretic use, urinary obstruction, or kidney injury. Persistent oliguria may signal acute kidney injury or other critical illness. Trends in urine output guide fluid management and dosing of potentially nephrotoxic medications.

Factors influencing urine output include age and body size, fluid intake, kidney disease, medications (such as diuretics and ACE inhibitors), hormones like antidiuretic hormone, hemodynamic status, urinary tract obstruction, and the use of external monitoring devices.