Prevention, removal of stones reflect changed thinking

Those were two of the most prominent themes in the stone-related take-home messages presented at the 2006 AUA annual meeting here, according to Glenn M. Preminger, MD, professor of urologic surgery and director of the Comprehensive Kidney Stone Center, Duke University Medical Center, Durham, NC.

Increased use of bariatric surgery for treatment of morbid obesity may raise the risk of stone formation.

"When the original gastric bypass surgery was being performed back in the 1970s, there were significant problems with hyperoxaluria and stone disease, and it was thought the procedure itself was to blame," Dr. Preminger said. "Because modern bariatric surgery does not usually cause the same type of malabsorption, it was thought stone disease would no longer be a significant problem. This is the first study in recent history to really examine the potential problem of stone formation following modern bariatric surgery."

Researchers at the University of California, San Francisco, also reported that modern bariatric surgery patients had lower urinary citrate values and elevated oxalate levels than those who had not undergone the surgery, yet "their global 24-hour urine parameters may not reflect an increased risk of urinary stone formation."

Calcium supplementation is associated with >60% reduction in nephrolithiasis rates in patients undergoing surgery for hyperparathyroidism.

Oral calcium supplementation resulted in a protective effect in patients with surgically managed hyperparathyroidism. Still, Dr. Preminger said, it's important to note that this University of California, San Francisco, study focused on a very select group of patients.

"We try to educate patients to maintain normal calcium intake under normal circumstances," he said. "If they want to be on calcium supplementation and they have an individual or family history of stones, it would be beneficial to check 24-hour urinary calcium after 4 months to make sure that supplemental calcium doesn't raise the risk of stone formation over the long term."

The recent study found that calcium supplementation also blunts production of calcium oxalate in patients on diets that include liberal oxalate intake.

"Lemonade therapy" increases urinary citrate and may offer an alternative for hypocitraturic calcium stone formers who cannot tolerate potassium citrate.

Patients consumed a mixture of 120 mL of reconstituted lemon juice and two liters of water each day, resulting in raised urinary citrate levels (364 mg to 718 mg) and decreased stone burden (37.2 mm² to 30.4 mm² ) over a mean treatment duration of 41.8 months.

The increase in citrate levels was not as dramatic as that seen in an age- and sex-matched control group of patients taking potassium citrate, but the so-called "lemonade therapy" does give another choice to patients who are unable to tolerate potassium citrate's side effects.

"Again, we should note that this therapy is useful in a select group of patients, those with mild to moderate hypocitraturia," said Dr. Preminger. "Potassium citrate also changed urinary pH by acting as an alkalinizing agent, while lemonade therapy has no effect on urinary pH."

A group from the University of Wisconsin, Madison, reported that calcium oxalate stone-formers managed with lemonade therapy sustained higher total volumes of urine and urinary citrate than did those on potassium citrate, while maintaining a favorable urine pH.