Rare-earth elements in urinary calculi.

In vitro studies have demonstrated that trace elements have inhibitory as well as stimulatory effects on the crystallization of urinary stones. Little is known about the activities of rare-earth elements (REEs) in the human body. Although their physiological role is unclear, an effect on calcium transport mechanisms is discussed. In the present study, ten kidney stones (six oxalate and four phosphate stones) were analyzed by neutron-activation analysis for their REE patterns. Urinary stones are capable of concentrating these elements, and some fractionation into light and heavy REEs appears to take place during deposition. Significantly elevated concentrations of heavy REEs such as europium, terbium, and lutetium were detected in phosphate stones as compared with oxalate stones (P < 0.005).