Management of Cystinuria

Pathophysiology and Diagnosis

• Diagnosis is confirmed through 24-hour urine collection showing elevated cystine levels, with stone analysis revealing characteristic hexagonal cystine crystals 4

First-Line Management Strategies

Hydration

• High fluid intake is particularly crucial in cystinuria to dilute urinary cystine concentration below 250 mg/L 1
• Oral intake of at least 4 liters per day is typically required, significantly higher than for other stone types 2

Dietary Modifications

• Limit sodium intake to 100 mEq (2,300 mg) or less daily, as lower sodium intake reduces cystine excretion 3
• Restrict animal protein intake to decrease cystine substrate load, as all animal-origin foods are rich in cystine and methionine (which metabolizes to cystine) 2

Urinary Alkalinization

• Potassium citrate is recommended to increase urinary pH to approximately 7.0, which enhances cystine solubility 5, 6
• Potassium citrate is preferred over sodium citrate to avoid increasing sodium load, which can increase cystine excretion 7

Second-Line Pharmacological Therapy

Cystine-Binding Thiol Drugs

• Offer cystine-binding thiol drugs to patients who are unresponsive to dietary modifications and urinary alkalinization, or have large recurrent stone burdens 5
• Tiopronin (alpha-mercaptopropionylglycine) is the preferred first choice due to better efficacy and fewer adverse events compared to D-penicillamine 5, 6

Monitoring and Follow-up

• Obtain a 24-hour urine specimen within six months of initiating treatment to assess response 5
• Annual 24-hour urine specimens are recommended for long-term follow-up, with more frequent monitoring for active stone formers 5
• Periodic blood testing to assess for adverse effects in patients on pharmacological therapy, particularly thiol drugs 6