Postrenal Failure

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

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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. 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]

VI. 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

VII. 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

VIII. 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)

IX. Labs

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

X. 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

XI. Differential Diagnosis

  1. Acute Kidney Injury
  2. Prerenal Failure

XII. 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

XIII. Management

  1. See Acute Kidney Injury Management
  2. Exclude reversible causes rapidly
  3. Renal Function recovery reflects obstruction duration

XIV. Prognosis

  1. See Acute Kidney Injury Prognosis

XV. Prevention

  1. See Prevention of Kidney Disease Progression

XVI. Resources

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

XVII. References

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

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