Cystine kidney stones

Cystinuria - the underlying cause

Cystine stones form in patients with cystinuria, an inherited (autosomal recessive) defect in the proteins that reabsorb the amino acid cystine from the urine in the kidney tubule. Affected individuals excrete large amounts of cystine, and because cystine is poorly soluble in acidic urine, it crystallises into stones.¹

Cystinuria affects roughly 1 in 7,000 people. Stone formation usually starts in childhood or adolescence and typically recurs throughout life. Many patients have a family history of stones from a young age.

How cystine stones are recognised

• Onset in a young patient with recurrent bilateral stones.
• Family history of stones from childhood or adolescence.
• Distinctive hexagonal crystals occasionally seen on urine microscopy.
• Positive urinary cystine test (sodium nitroprusside test) with confirmation by 24-hour quantitative urinary cystine.
• Stone composition analysis confirms cystine.

Imaging features

On CT, cystine stones are moderately dense and often appear smoother-edged than calcium stones. Unlike calcium stones, cystine stones are relatively hard and do not break well with shockwave lithotripsy. Ureteroscopy with Holmium laser is generally the preferred treatment.^{1, 2}

Treatment

The usual surgical options apply, but with a few important modifications:

• Flexible ureteroscopy with Holmium laser is typically preferred over ESWL because cystine stones are resistant to shockwaves.
• PCNL is used for large stones > 2 cm.
• Medical treatment is central - even after a stone is cleared, active prevention is essential because of the high recurrence rate.

Medical management and prevention

Because cystine stones recur so readily, lifelong medical management is the cornerstone of care. The main strategies are:¹

• Very high fluid intake - the target urine output for cystinuric patients is usually more than 3 L/day, including fluid during the night.
• Urinary alkalinisation with potassium citrate, aiming for a urine pH of around 7.0-7.5 - cystine is much more soluble in alkaline urine.
• Moderate dietary sodium - high sodium worsens cystine excretion.
• Moderate dietary animal protein - reduces methionine (a cystine precursor) intake.
• Thiol-binding drugs (tiopronin, D-penicillamine) for patients in whom fluid and alkalinisation alone are insufficient. These medications form soluble complexes with cystine but have important side-effects and require specialist monitoring.

The importance of a dedicated team

Cystinuria is best managed in partnership with a renal physician who specialises in metabolic stone disease. Dr Kooner works with renal physician colleagues to provide long-term surveillance, medication titration, and regular imaging for cystinuric patients. Combined care typically involves:

• Urology for surgical clearance of stones as they occur.
• Renal medicine for metabolic management and medication.
• Regular low-dose CT or ultrasound imaging, interval depending on disease activity.

Related pages

References

1. Skolarikos A, et al. EAU Guidelines on Urolithiasis. 2025.
2. Pearle MS, et al. Surgical Management of Kidney and Ureteral Stones: AUA Guideline (2026).