Paeds · nephrology-urology-fluids-and-electrolytes
Oliguria, anuria and urinary obstruction
Also known as Paediatric oliguria · Anuria in children · Post-renal obstruction · Obstructive uropathy · Post-obstructive diuresis · Urinary tract obstruction in children
Fellowship guide to oliguria, anuria and urinary obstruction in children: the urine output thresholds that define oliguria and anuria, the pre-renal, renal and post-renal framework with post-renal obstruction the focus, the pathophysiology of obstructive nephropathy where raised hydrostatic pressure collapses filtration, the emergency decompression of the urinary tract by catheter or nephrostomy, and the diagnosis and fluid management of post-obstructive diuresis that follows relief of a chronic obstruction.
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Target exams
Red flags
- Anuria in a neonate or infant suggesting bilateral renal agenesis, posterior urethral valves, or a solitary kidney with obstruction
- A palpable distended bladder with a poor urinary stream in a male infant indicating posterior urethral valves
- Bilateral hydronephrosis on antenatal or postnatal ultrasound with oliguria after birth
- Post-obstructive diuresis with urine output above 3 mL per kg per hour persisting beyond 24 hours after decompression, risking hypovolaemia and electrolyte loss
- Hyperkalaemia with ECG changes complicating an obstructive acute kidney injury requiring immediate intravenous calcium gluconate
- Septic shock from pyelonephritis or pyonephrosis behind an obstructed system requiring urgent decompression and antibiotics
- A child with a neurogenic bladder and recurrent urinary tract infections presenting with overflow incontinence mistaken for normal voiding
- Uraemic encephalopathy, pericardial rub, or a bleeding diathesis signalling the need for urgent renal replacement therapy in obstructive renal failure
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- Defines oliguria and anuria by urine output thresholds and recognises oliguria as a clinical sign rather than a diagnosis
- Classifies the cause of reduced urine output as pre-renal, renal, or post-renal and identifies a palpable bladder as obstruction
- Performs emergency bladder catheterisation to relieve a suspected obstruction and requests a renal ultrasound
- Applies the pathophysiology of obstructive nephropathy to explain why prompt decompression preserves renal function
- Diagnoses and manages post-obstructive diuresis with controlled fluid and electrolyte replacement after relief of a chronic obstruction
- Coordinates paediatric nephrology and urology for the definitive repair of posterior urethral valves, ureteropelvic junction obstruction, and neurogenic bladder
- Urine output thresholds for oliguria and anuria and the post-renal causes of obstruction in children
- Emergency decompression of the urinary tract by catheter or nephrostomy
- Recognition and fluid management of post-obstructive diuresis
- Recognises a child with anuria and a palpable bladder and acts on obstruction before investigating the cause
- Communicates the plan for decompression and definitive surgical repair to a family
- Counsels on the long-term renal surveillance after relief of an obstructive uropathy
- Level 1: Recognition of oliguria and anuria and the emergency of a distended bladder
- Level 2: Catheter decompression, renal ultrasound, and post-obstructive diuresis monitoring
- Level 3: Coordination of definitive urological repair and long-term nephrology follow-up
- Urine output definitions of oliguria and anuria and the post-renal causes of obstruction
- Pathophysiology of obstructive nephropathy and the consequences of delayed decompression
- Post-obstructive diuresis definition, diagnosis, and management
- Bedside assessment of the oliguric child including abdominal palpation for a distended bladder
- Interpretation of the renal ultrasound for hydronephrosis and the level of obstruction
- Structured explanation of decompression, post-obstructive diuresis monitoring, and definitive repair
- Definitions of oliguria and anuria and the triage of pre-renal, renal, and post-renal causes
- Posterior urethral valves as the leading cause of lower urinary tract obstruction in male infants
- Post-obstructive diuresis recognition and fluid replacement strategy
- Recognition of urinary obstruction as a reversible cause of acute kidney injury requiring emergency decompression
- Performance of bladder catheterisation and escalation to urology for nephrostomy
- Family communication around surgical repair, dialysis if needed, and long-term kidney health
- Canadian approach to paediatric urinary obstruction and regional retrieval to paediatric urology centres
- Urinary tract dilation classification to risk-stratify hydronephrosis for surveillance versus intervention
- Long-term kidney surveillance after obstructive uropathy and the prevention of progression to chronic kidney disease
Overview & Definition
A child whose urine output has fallen to a trickle, or stopped altogether, is sending a signal that demands an answer before the biochemistry turns dangerous. Oliguria and anuria are not diagnoses but clinical signs measured at the bedside, and the first question is always whether the drop in output reflects a kidney that is under-perfused, a kidney that is injured, or a kidney that is blocked. This page focuses on the third possibility, the obstructed urinary tract, because it is the most readily reversible cause of acute kidney injury in children and because it carries a distinctive and testable complication in the period after the block is relieved. [1]
The thresholds that frame the whole assessment come from the KDIGO acute kidney injury criteria, summarised by Kellum and Lameire. Oliguria is a urine output below 0.5 mL per kg per hour for six hours or more, and anuria is the more severe reduction, defined by KDIGO as a urine output below 0.3 mL per kg per hour for 24 hours or more, or complete absence of urine for 12 hours or more. A stricter bedside convention defines anuria as below 0.1 mL per kg per hour or below 1 mL per kg per day, and the absence of any urine on catheterisation is the practical red flag that distinguishes true anuria from retention or a missed collection. [1]
The urgency comes from the speed with which a blocked kidney fails and the completeness with which it can recover if the obstruction is relieved early. Obstructive nephropathy is the term for the structural and functional injury that follows a block anywhere from the renal pelvis to the urethra, and it is the only major cause of paediatric acute kidney injury in which a single intervention, decompression, can reverse the entire process within hours. Delay converts a reversible problem into permanent scarring, which is why the obstructed child is a surgical and not merely a medical emergency. [3]
References12ShowHide
- [1]Kellum JA, Lameire N Diagnosis, evaluation, and management of acute kidney injury: a KDIGO summary (Part 1). Crit Care, 2013.PMID 23394211
- [2]Molitoris BA Low-Flow Acute Kidney Injury: The Pathophysiology of Prerenal Azotemia, Abdominal Compartment Syndrome, and Obstructive Uropathy. Clin J Am Soc Nephrol, 2022.PMID 35584927
- [3]Nørregaard R, Mutsaers HAM, Frøkiær J, Kwon TH Obstructive nephropathy and molecular pathophysiology of renal interstitial fibrosis. Physiol Rev, 2023.PMID 37440209
- [4]Hafizar, Wahyudi I, Situmorang GR, Risky Raharja PA, Rodjani A Long-term renal outcomes in children with posterior urethral valves: a systematic review and meta-analysis. Pediatr Surg Int, 2026.PMID 42323785
- [5]Robinson CH, Rickard M, Jeyakumar N, Smith G, Richter J, Van Mieghem T, et al Long-Term Kidney Outcomes in Children with Posterior Urethral Valves: A Population-Based Cohort Study. J Am Soc Nephrol, 2024.PMID 39167453
- [6]López Pereira P, Martinez Urrutia MJ, Jaureguizar E Initial and long-term management of posterior urethral valves. World J Urol, 2004.PMID 15558286
- [7]Leinum LR, Berthelsen C, Azawi N Post-obstructive diuresis; underlying causes and hospitalization. Scand J Urol, 2020.PMID 32449436
- [8]Baum N, Anhalt M, Carlton CE Jr, Scott R Jr Post-obstructive diuresis. J Urol, 1975.PMID 1142500
- [9]Cai PY, Lee RS Ureteropelvic Junction Obstruction/Hydronephrosis. Urol Clin North Am, 2023.PMID 37385700
- [10]Woolf AS, Thiruchelvam N Congenital obstructive uropathy: its origin and contribution to end-stage renal disease in children. Adv Ren Replace Ther, 2001.PMID 11533916
- [11]Nguyen HT, Phelps A, Coley B, Darge K, Rhee A, Chow JS 2021 update on the urinary tract dilation (UTD) classification system: clarifications, review of the literature, and practical suggestions. Pediatr Radiol, 2022.PMID 34981177
- [12]Stein R, Bogaert G, Dogan HS, Hoen L, Kocvara R, Nijman RJM, et al EAU/ESPU guidelines on the management of neurogenic bladder in children and adolescent part I diagnostics and conservative treatment. Neurourol Urodyn, 2020.PMID 31724222