Urinary tamm-horsfall protein increased after potassium citrate therapy in calcium stone formers

Abstract

Objectives To evaluate the effect of oral potassium citrate therapy on urinary excretion rates of citrate, Tamm-Horsfall protein (THP), and on calcium oxalate monohydrate crystal agglomeration inhibition [tm], in patients with recurrent calcium stone formation. Methods To evaluate the effect of oral therapy with potassium citrate on urinary citrate, THP, and [tm], 24-hour urine samples were collected before and at least 2 months after initiation of oral potassium citrate therapy in 33 calcium stone-forming patients who had no dietary restrictions. The citrate concentration was measured by an adaptation of a citrate lyase method. Urinary disaggregated THP concentration was determined with a quantitative enzyme-linked immunosorbent assay. The [tm] was determined by observing the effects of patients' urine, before and after oral potassium citrate therapy, on the uptake of 45Ca 2+ onto the surfaces of added preformed calcium oxalate crystals in a supersaturated solution of calcium oxalate, using the in vitro kinetic method described by other investigators. Results We observed an increased urinary excretion rate of citrate from a mean of 1.9 mmol/24 h prealkali to 2.6 mmol/24 h postalkali ( P < 0.0004) and of THP from a mean of 94.0 mg/24 h prealkali to 199.3 mg/24 h postalkali ( P <0.0016). A corresponding increase in [tm] from a mean of 177.1 minutes prealkali to 221.0 minutes postalkali ( P < 0.024) was also observed. Conclusions To our knowledge this is the first report correlating increased urinary citrate with THP excretion rate following oral alkalinization with potassium citrate in calcium stone formers. Of clinical importance is the corresponding increase in [tm], which was previously shown to be inversely related to stone-forming activity. Moreover, urinary citrate and THP are known to have a synergistic effect on [tm]. Our data suggest that the effectiveness of potassium citrate therapy in calcium stone-forming patients may, at least in part, be due to increased levels of THP.