Neutral Phosphate for Kidney Stones

Kidney stones are common and often come back. One reason may be that some people with calcium stones have low phosphate levels in the blood and lose too much phosphate through the kidneys. They may also have high calcium in the urine, which raises the chance of forming stones. In older studies, high doses of phosphate supplements lowered urine calcium and appeared to reduce stone formation, but they sometimes caused stomach and bowel side effects, and phosphate is no longer used for stone prevention. This small pilot study will test a much lower dose of neutral phosphate (250 mg twice daily) for 2 weeks in adults with recurrent calcium oxalate kidney stones, high urine calcium, and low blood phosphate. Participants will collect a 24-hour urine sample and have blood drawn before and after the 2-week period. The study will look at whether the low dose reduces urine calcium and the risk of stone formation in urine. The results will help decide whether a larger study is warranted.