uric acid stone (urate nephropathy, gouty nephropathy)

Etiology

predisposing factors

• 25% of patients with gout have uric acid stones
• urine pH is often very acidic
• hyperuricosuria
• dietary protein excess can predispose to uric acid stones
• colectomy & ileostomy predispose to uric acid stones because of decreased intestinal ureolysis & increased loss of water & alkali
• chronic diarrhea
• metabolic syndrome
• lymphoproliferative & hematologic disorders
  • tumor lysis syndrome

Laboratory

• urinalysis: urine is often very acidic
• serum uric acid & urine uric acid levels are often normal
• urine pH < 6.0 is risk factor
• 24 hour urine urate
  • > 1 g/day is risk factor
  • target is 100-300 mg/day

Radiology

• uric acid stones are radiolucent
• visualized by ultrasound or computed tomography (CT)

Management

• increased intake of fluids
• decreased protein intake
• alkalinizing urine to pH of 6.5
  • helps prevent uric acid stone formation
  • dissolves existing stones
  • potassium citrate treatment of choice
  • NaHCO3 or citrate (Bicitra)
• allopurinol or hypouricemic agent
  • not as effective as urine alkalinization, but helpful in patients with hyperurisocuria
  • used as prophylaxis for tumor lysis syndrome

More general terms

• urinary calculus (stone, nephrolithiasis, urolithiasis)
• nephropathy

Additional terms

• hyperuricemia
• hyperuricosuria
• urate; uric acid