Postrenal Failure

Aka: Postrenal Failure, Postrenal Azotemia, Postrenal Failure Causes, Acute Postrenal Failure, Postrenal Obstruction, Hydronephrosis, Urinary Outflow Obstruction, Urinary Tract Obstruction, Obstructive Uropathy

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II. Definitions

  1. Hydronephrosis
    1. Abnormal dilation of renal calices and renal Pelvis
    2. Develops as a result of distal Urinary Tract Obstruction (e.g. Ureterolithiasis, ureteral stricture, Benign Prostatic Hyperplasia)

III. Epidemiology

  1. Accounts for 3-10% of Acute Renal Failure cases
  2. More common in elderly

IV. Pathophysiology

  1. Urinary Tract Obstruction
  2. Results in renal Pelvis dilatation
  3. Progressive decrease in Renal Function
    1. Increased intratubular pressure
    2. Decreased capillary filtration pressure

V. History

  1. Degree of obstruction
    1. Complete obstruction (and timing of last void)
    2. Decreased urinary flow or stream
  2. New medications or substance use
    1. See Medication Causes of Postrenal Failure
  3. Back pain
    1. Cauda Equina Syndrome symptoms
    2. Flank Pain
  4. Urologic procedures
    1. Similar obstructive symptoms
  5. Associated symptoms
    1. Gross Hematuria (consider larger catheter >=22 Fr, three way catheter)
    2. Urinary Tract Infection symptoms

VI. Causes: Most Common

  1. Most Common causes in Adults
    1. Benign Prostatic Hyperplasia (BPH)
    2. Neurogenic Bladder
    3. Pelvic masses
    4. Ureterolithiasis
  2. Most common causes in children
    1. Neurologic conditions (17%)
    2. Urinary Tract Infection (13%)
    3. Medications (13%)
    4. Local inflammation (7%)
    5. Local invasive cancer (6%)
    6. Benign obstructive causes (6%)
      1. Constipation (13%)
    7. Incarcerated Hernias (2%)
    8. Gatti (2001) J Urol 165(3):918-21 [PubMed]

VII. Causes: Postrenal Failure (Renal outflow obstruction)

  1. See Medication Causes of Postrenal Failure
  2. Intrarenal (distal tubules)
    1. Nephrolithiasis
    2. Multiple MyelomaProtein
    3. Medications predisposing to Uric Acid crystals (Hyperuricemia, Gout)
      1. See Medication Causes of Postrenal Failure
      2. Includes Methotrexate, Acyclovir, and Protease Inhibitors (e.g. Indinavir or Crixivan)
  3. Extra-Ureteral Obstruction
    1. Prostate Cancer
    2. Bladder Cancer
    3. Cervical Cancer
    4. Retroperitoneal fibrosis
    5. Accidental ureteral ligation during pelvic surgery
  4. Ureteral Obstruction (Bilateral in Renal Failure)
    1. Ureterolithiasis
    2. Thrombosis
    3. Pyogenic debris or sloughed papillae
    4. Edema from retrograde pyelography
  5. Bladder neck obstruction
    1. Benign Prostatic Hypertrophy (BPH)
    2. Neurogenic Bladder
    3. Prostate Cancer
    4. Bladder Cancer
    5. Autonomic Neuropathy
    6. Ganglionic blocking medication
  6. Urethral Obstruction
    1. Urethral valves
    2. Urethral Stricture

VIII. Symptoms

  1. May be asymptomatic in chronic, progressive obstruction (e.g. neurogenic Bladder, BPH)
  2. Severe lower Abdominal Pain or Groin Pain (colic-type attacks)
  3. Lower Abdominal Distention

IX. Signs

  1. Mass at flank, suprapubic, or central Abdomen
  2. Abdominal exam
  3. Pelvic exam
  4. Rectal Exam
  5. Anuria (Indicates obstruction in 90% cases)

X. Labs

  1. See Renal Function
  2. Urine Sediment
    1. Normal sediment
    2. Hematuria
    3. Pyuria
    4. Crystals

XI. Imaging

  1. Bladder Ultrasound
    1. Measure post-void Residual Volume without catheterization
  2. Limited Ultrasound for Acute Renal Colic (or formal Ultrasound)
    1. Evaluate for Hydronephrosis

XII. Differential Diagnosis

  1. Acute Kidney Injury
  2. Prerenal Failure

XIII. Diagnostic Testing

  1. Post-void residual >100 ml
    1. Indicates Bladder outlet obstruction
  2. Ultrasound or Intravenous Pyelogram
    1. Dilated ureters or renal Pelvis
  3. Abdominal CT or Abdominal MRI
  4. Percutaneous Nephrostomy drainage trial

XIV. Management

  1. See Acute Kidney Injury Management
  2. Exclude reversible causes rapidly
  3. Renal Function recovery reflects obstruction duration
  4. Consult urology (esp. for recent urologic procedures in last 3 months)
  5. Manage Benign Prostatic Hyperplasia
    1. Start Tamsulosin
  6. Urethral Catheterization
    1. Consider indwelling Foley Catheter (esp. for >1 L post-void residual)
    2. Trial of void typically if indwelling catheter in 1-3 days (1 week in severe or outpatient cases)

XV. Complications: Obstructive Uropathy

  1. Post-Renal Failure
  2. Post-obstructive diuresis
    1. Voiding >200 ml/h for >=2 hours (or 3-4 L/day)
    2. Associated with Hypotension, Tachycardia, Syncope
    3. Associated with Electrolyte abnormalities (e.g. Hyponatremia, Hypokalemia, Hypomagnesemia)

XVI. Prognosis

  1. See Acute Kidney Injury Prognosis

XVII. Prevention

  1. See Prevention of Kidney Disease Progression

XVIII. Resources

  1. Acute Kidney Injury Guidelines
    1. http://www.renal.org/clinical/guidelinessection/AcuteKidneyInjury.aspx

XIX. References

  1. Anderson (8/15/1993) Hospital Practice, p. 61-75
  2. Broder (2025) Crit Dec Emerg Med 39(7): 24-6
  3. Reilly (2026) Obstructive Uropathy, EM:Rap, 2/2/2026
  4. Meyer (2007) N Engl J Med 357(13): 1316-25 [PubMed]
  5. Rahman (2012) Am Fam Physician 86(7): 631-9 [PubMed]
  6. Singri (2003) JAMA 289(6):747-51 [PubMed]

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