Cystine Kidney Stones (Cystinuria)

Cystinuria is a genetic condition that causes cystine to build up in your urine. Cystine is an amino acid, a building block of protein. Most people have very little cystine in their urine. People with cystinuria have too much.

When cystine levels get too high, it forms crystals and then stones in the kidneys. These cystine stones are hard and can cause severe pain. They block urine flow and damage kidney tissue. Cystinuria affects about 1 in 7,000 people. It usually appears before age 40, often in childhood or young adulthood.

The condition is inherited from both parents. You need two copies of the gene mutation to develop cystinuria. Managing this condition requires lifelong monitoring. The goal is preventing new stones from forming and protecting kidney function.

• Severe pain in the side or back, often called flank pain
• Sharp pain in the lower abdomen or groin
• Blood in the urine, making it pink, red, or brown
• Frequent urge to urinate
• Pain or burning during urination
• Cloudy or foul-smelling urine
• Nausea and vomiting
• Fever and chills if infection develops
• Difficulty passing urine or weak urine stream

Some people have no symptoms until a stone becomes large enough to cause blockage. Small stones may pass without notice. Recurring stones are common with cystinuria.

Cystinuria is caused by mutations in genes that control cystine transport in the kidneys. The SLC3A1 and SLC7A9 genes are most commonly affected. These genes help kidneys reabsorb cystine from urine back into the bloodstream. When they do not work properly, cystine stays in the urine. High cystine levels lead to crystal and stone formation, especially in acidic urine.

You inherit cystinuria from both parents who carry the gene mutation. Risk factors include family history of cystinuria or early kidney stones. Dehydration makes stones more likely by concentrating urine. Acidic urine with a pH below 7.0 allows cystine crystals to form more easily. Diet does not cause cystinuria, but it can affect stone formation risk.

Doctors diagnose cystinuria through urine tests that measure cystine levels. A 24-hour urine collection shows how much cystine your body excretes. Imaging tests like CT scans or ultrasounds reveal stones in the kidneys or urinary tract. Chemical analysis of passed stones confirms they are made of cystine.

Monitoring urine pH is essential for managing cystinuria. Cystine dissolves better in alkaline urine with a pH above 7.0. Regular urine pH testing helps guide treatment to prevent new stones. Rite Aid offers testing that includes urine pH monitoring. This helps you track whether your prevention plan is working.

• Drink 3 to 4 liters of water daily to dilute urine and prevent crystal formation
• Spread fluid intake throughout the day, including before bed and during the night
• Take medications that alkalinize urine, raising pH above 7.0 to 7.5
• Use potassium citrate or sodium bicarbonate to increase urine pH
• Reduce sodium intake to less than 2,000 mg daily, as salt increases cystine excretion
• Limit animal protein to 0.8 to 1.0 grams per kilogram of body weight daily
• Take thiol drugs like tiopronin or penicillamine if stones continue despite other measures
• Monitor urine pH regularly at home using test strips
• Have regular imaging to check for new stone formation
• Consider surgical removal for large stones that cause symptoms or blockage