oliguria

Oliguria is a clinical term describing abnormally low urine production. In adults, it is commonly defined as urine output of less than 400 milliliters per day, though some definitions use a rate below 0.5 milliliters per kilogram per hour. Oliguria may be an early sign of acute kidney injury or a response to reduced effective circulating volume. It is distinct from anuria, which is virtually no urine output (often defined as less than 100 milliliters per day).

Common etiologies are grouped as prerenal, intrarenal, and postrenal. Prerenal causes include dehydration, blood loss, sepsis, heart failure, liver disease, and large-volume diuresis—conditions that reduce renal perfusion. Intrarenal causes include acute tubular necrosis from ischemia or nephrotoxins (such as certain drugs and contrast agents), glomerulonephritis, or interstitial nephritis. Postrenal causes are urinary tract obstructions from stones, tumors, or prostatic hypertrophy.

Evaluation involves careful monitoring of urine output and fluid balance, vital signs, and laboratory testing. Serum creatinine and blood urea nitrogen, electrolytes, and urinalysis are commonly obtained. Urine studies may include urine sodium and osmolality, and the fractional excretion of sodium. Renal ultrasound or other imaging can identify obstruction or structural abnormalities.

Management focuses on treating the underlying cause and correcting hemodynamic status. In prerenal states, appropriate fluid resuscitation and volume optimization are central. Avoid nephrotoxins and adjust medications as needed. In established acute kidney injury with oliguria, diuretics may be used in some cases but do not improve outcomes; renal replacement therapy may be required for refractory fluid overload, hyperkalemia, or uremia.

Prognosis depends on the underlying cause and the timeliness of intervention; prolonged oliguria is associated with higher risk of renal injury and adverse outcomes.