Anuria

Anuria is the medical term for the complete absence of urine production. In adults, it is commonly defined as urine output of less than 100 milliliters per day, though definitions vary. Anuria is a sign of severe kidney dysfunction and requires urgent evaluation to identify and treat the underlying cause.

Causes are typically categorized as pre-renal, renal (intrinsic), or post-renal. Pre-renal causes include severe dehydration, hemorrhage, or septic shock leading to reduced renal perfusion. Renal causes involve intrinsic kidney injury such as acute tubular necrosis from ischemia or nephrotoxic agents, severe glomerulonephritis, or acute interstitial nephritis. Post-renal causes are obstructions that prevent urine flow, such as bilateral ureteral stones, tumors, or bladder outlet obstruction from conditions like benign prostatic hyperplasia.

Pathophysiology centers on a critical reduction or cessation of filtrate formation due to poor perfusion, obstruction, or direct nephron injury. Prolonged anuria can lead to uremia and life-threatening electrolyte and fluid imbalances.

Clinical features often include a sudden drop in urine output with symptoms related to the underlying cause, such as dehydration, pain from stones, or signs of obstruction. If urine output remains absent, signs of volume overload, hyperkalemia, metabolic acidosis, and rising serum creatinine may develop.

Diagnosis relies on confirming very low urine output, ruling out a patent bladder (bladder catheterization), and evaluating kidney function and structure. Laboratory tests, urinalysis, and imaging (ultrasound or CT) help identify prerenal, intrarenal, or postrenal etiologies.

Management focuses on treating the underlying cause and supporting kidney function. Fluid resuscitation for hypovolemia, relief of obstruction, avoidance of nephrotoxins, and supportive care; dialysis may be required for severe electrolyte disturbances, uremia, or persistent anuria despite etiologic treatment. Prognosis depends on timely identification and reversal of the underlying cause.