Cystinuria is a disorder characterized by stones in the kidney, ureter, and bladder. It is caused by excessive excretion of certain amino acids (protein building blocks) due to a genetic abnormality. (See also nephrolithiasis).

Cystinuria is an inherited autosomal recessive disorder. The kidneys do not adequately resorb certain amino acids during the filtering process, resulting in excess excretion of these amino acids. The amino acids may precipitate (solids separate from liquids) and form crystals or stones in the kidneys, ureters, or bladder.

The disorder is usually diagnosed after an episode of stones, where analysis of the composition of the stones indicates cystine. Less than 3% of known urinary tract stones are cystine stones.

Cystinuria affects approximately 1 out of 10,000 people. Cystine stones are most common in young adults under age 40.

• Flank pain or pain in the side or back
  • On one side only (unilateral) or -- rarely, both sides
  • Often severe
  • May be progressive, getting increasingly worse over days
  • May travel or radiate to lower flank, pelvis, groin, genitals
• Blood in the urine

Symptoms may indicate kidney stones. The doctor will not be able to determine the presence or cause of the stones with only a physical examination.

Straining the urine may capture urinary tract stones when they are excreted. An analysis of the stones shows cystine. A urinalysis may show sediment and cystine crystals. A 24-hour urine collection shows an excess of cystine.

An abdominal CT scan, abdominal MRI, or abdominal ultrasound may show a presence of stones in the urinary tract. An IVP (intravenous pyelogram) may show stones in the urinary tract.