Urinary tract stones: how to eliminate and prevent them

Urinary tract stone disease is relatively common. It is estimated to affect around 10% of men and 5% of women, typically between the ages of 30 and 50. In Italy alone, there are approximately 100,000 new cases each year, with a high recurrence rate.

Some genes have been identified that may play a role in the formation of kidney stones, and nephrolithiasis is known to have a familial pattern and significant heritability.

“Urine is composed of water and dissolved substances that the body needs to eliminate. Some of these, such as calcium, oxalates, uric acid, and cystine, tend to crystallize and can reach concentrations that make it difficult for them to stay dissolved. This leads to the formation of small crystals that can clump together to form larger stones,” explains Dr. Choussos.

The crystallization process can be counteracted by magnesium and citrate, both important inhibitors of stone formation. Low levels of these substances in urine increase the risk of developing stones.

Types of Kidney Stones

The main types of kidney stones include:

• Calcium stones
• Struvite stones (composed of magnesium ammonium phosphate)
• Uric acid stones
• Cystine stones

Calcium stones account for 75% of all kidney stones. Epidemiological studies have shown an inverse relationship between dietary calcium intake and the incidence of stones, especially in individuals experiencing their first episode.

Uric acid stones, which make up 6% of cases, are radiolucent (i.e., not visible on standard X-rays) and are typically detected via ultrasound. They are associated with urine pH below 5.5 and a high intake of purines (found in foods like legumes, fish, meat extracts, and gravies). About 25% of patients with uric acid stones also suffer from gout.

Some medications can also lead to stone formation by precipitating in the urine. It is important to note that stone composition affects both diagnosis and treatment options.

Once formed in the kidney, most stones are expelled spontaneously through the urinary tract. However, their passage through the ureter and bladder can cause severe pain (renal colic), and if stones remain in the kidney or ureter, they can trigger infections. Generally:

• Stones ≤ 4 mm are likely to pass on their own.
• Stones > 8 mm often require surgical intervention.

With medical expulsive therapy (MET), stones measuring 5–8 mm may pass, especially if located in the distal ureter. The larger the stone, the lower the chance of spontaneous expulsion, and the higher the likelihood of surgery.

Key indications for surgical treatment include:

• Severe pain
• Infection
• Urinary tract obstruction

An infection associated with obstruction is a serious medical emergency due to the risk of urosepsis and must be treated urgently.

“The vast majority of symptomatic urinary stones today are treated with minimally invasive endoscopic techniques. Open surgery is now reserved for rare and complex cases,” says Dr. Choussos.

At our center, we treat various forms of renal, ureteral, and bladder urolithiasis with the following procedures:

• Rigid and flexible ureterorenoscopy with Holmium laser lithotripsy for ureteral and renal stones: a minimally invasive endoscopic technique in which a small scope is introduced through the bladder and ureter to directly visualize and fragment the stone using laser energy.
• Percutaneous nephrolithotomy (PCNL) for renal stones larger than 2 cm.
• Mini and micro percutaneous nephrolithotomy for renal stones smaller than 2 cm.
• Endoscopic cystolithotripsy for bladder stones.

Prevention is the most effective strategy against kidney stone formation. Regardless of individual risk, all stone-forming patients should follow these recommendations:

• Drink at least 2.5–3 liters of water per day, ensuring a 24-hour urine output of at least 2.5 liters to dilute stone-forming substances.
• Adopt a balanced diet rich in vegetables and fiber, while avoiding excessive use of vitamin supplements.
• Limit sodium and animal protein intake.
• Do not excessively restrict dietary calcium. Many patients with calcium-based stones have normal urinary calcium levels, and reducing calcium intake can worsen stone formation by increasing oxalate absorption in the gut. Low dietary calcium can also negatively affect bone mineralization, increasing the risk of osteoporosis, particularly in women.
• Avoid fructose-containing beverages, which can increase stone formation.
• Maintain a healthy weight through a normocaloric diet, as overweight is a known risk factor.

“Patients who are highly motivated to prevent recurrence, those with multiple relapses, a single functioning kidney, or children under 16 years old with nephrolithiasis should be referred to a specialist in kidney stone prevention. The most common mistake is to treat kidney stones only when symptoms appear, such as during a renal colic. Yet, the disease primarily develops during asymptomatic periods,” concludes Dr. Choussos.