What conditions increase the risk for urolithiasis?

Risk Factors for Urolithiasis

Hypercalciuria, polycystic kidney disease, and hyperoxaluria all increase the risk for urolithiasis, while well-hydrated status and a diet high in fruits and vegetables are protective factors against stone formation. 1

Major Risk Factors for Urolithiasis

Metabolic Risk Factors

• Hypercalciuria: Elevated urinary calcium excretion is a major risk factor for calcium stone formation, which accounts for approximately 80% of all kidney stones 1
• Hyperoxaluria: Increased urinary oxalate excretion significantly raises the risk of calcium oxalate stone formation by increasing urinary supersaturation 1
• Hypocitraturia: Low urinary citrate levels reduce the inhibition of calcium crystal formation and aggregation, increasing stone risk 1
• Hyperuricosuria: Elevated urinary uric acid can promote calcium oxalate stone formation and is associated with uric acid stones 1

Medical Conditions

• Polycystic Kidney Disease (PKD): Significantly increases risk of stone formation through both metabolic and mechanical factors 2

  • In PKD patients, uric acid stones (56.6%), calcium oxalate (46.6%), and calcium phosphate (20%) stones are common 2
  • Hypocitraturia and low urine pH are particularly common in PKD patients with stones 2

• Primary Hyperparathyroidism: Causes hypercalciuria and increases stone risk 1

• Intestinal Malabsorption: Leads to absorptive hyperoxaluria and hypocitraturia 3

  • Particularly evident in conditions like cystic fibrosis, where absorptive hyperoxaluria increases stone risk 3

Dietary and Lifestyle Factors

• Low Fluid Intake: Insufficient hydration leads to concentrated urine and increased supersaturation of stone-forming salts 1
• High Sodium Intake: Increases urinary calcium excretion 1
  • Guidelines recommend limiting sodium to 2,300-3,000 mg daily 1
• High Animal Protein Consumption: Increases urinary calcium and uric acid excretion while reducing citrate excretion 1
• High Oxalate Foods: Excessive consumption of high-oxalate foods increases urinary oxalate excretion 1
• Vitamin C Supplements: May increase oxalate generation and excretion 1

Protective Factors Against Urolithiasis

• Well-Hydrated Status: Maintaining high fluid intake to produce urine volume >2L/day significantly reduces stone risk 1

  • Increased fluid intake is the most effective intervention for preventing recurrent stones 1

• Diet High in Fruits and Vegetables:

  • Increases urinary citrate excretion which inhibits stone formation 1
  • Provides dietary potassium which reduces urinary calcium excretion 1
  • Helps maintain a more alkaline urine pH, which prevents certain stone types 1

• Adequate Dietary Calcium: Contrary to previous beliefs, normal calcium intake (1,000-1,200 mg daily) reduces stone risk by binding dietary oxalate in the gut 1

Other Risk Factors

• Obesity and Metabolic Syndrome: Associated with increased risk of stone formation 4

  • Women with higher BMI face particularly increased risk 4

• Diabetes: Associated with increased risk of stone formation 1

• Gout: Increases risk of uric acid stones 1

• Anatomical Abnormalities: Urinary stasis increases risk of stone formation 1

Clinical Implications

• Stone formers have an increased risk of end-stage renal disease (ESRD) compared to non-stone formers (HR: 2.09) 5
• The 5-year recurrence rate for kidney stones is 35-50% without specific preventive treatment 1
• Preventive strategies should target the specific metabolic abnormalities identified in 24-hour urine collections 1
• Pharmacologic interventions including thiazides, citrates, and allopurinol can reduce recurrence risk in patients with specific metabolic abnormalities 1

Pitfalls and Caveats

• Low dietary calcium was previously thought to reduce stone risk, but evidence now shows this actually increases risk by allowing more dietary oxalate absorption 1
• Calcium supplements may increase stone risk if taken between meals, unlike dietary calcium which is protective when consumed with meals 1
• Stone risk factors vary by age and sex, requiring individualized assessment 1, 4
• The presence of Oxalobacter formigenes (oxalate-degrading bacteria) in the gut may influence oxalate handling and stone risk 1, 3