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Abnormal urine composition is believed to cause renal stone formation. Although many people, healthy and otherwise, exhibit calcium oxalate crystalluria in their concentrated morning urines, only some form stones. This observation suggests that kidney stone patients have an “evil urine,” deficient in stone inhibition factors. Though renal stone patients tend to be hypercalciuric, hyperoxaluric, and hypocitraturic, these factors alone do not allow the treating physician to clearly predict which patients will form more stones.
While kidney stone disease is prevalent in all industrialized nations, Louisiana and the Gulf States comprise what is known as the “Stone Belt” where kidney stones occur at a rate of approximately 5%(1). Of patients who initially form kidney stones, about half recur without therapy. The recurrence rate without treatment is about 10% at 1 year, 33% at 5 years, and 50% at 10 years(2). The search for reliable, rapid, and accurate tools to enable the clinician to diagnose, predict, and prevent kidney stone recurrence continues.
A new tool developed at Ochsner was found to be predictive of stone formation rates 3,4) by evaluating the effect of calcium oxalate stone former (CaOx SF) outpatient urine on in vitro calcium oxalate monohydrate (COM) crystal agglomeration inhibition [tm]. Using enzyme-linked immunoadsorbent assay (ELISA), we examined the consequences of the removal of Tamm-Horsfall protein (THP), the dominant protein in the urine, by ultrafiltration and determined the concentration of disaggregated THP in unfiltered and ultrafiltered urine(4). It was clear from our results that THP and citrate, as well as their interaction, increased [tm](4). Moreover, we showed that THP and citrate could be regulated by alkali medication(5).
Using [tm], the effectiveness of alkali medication could be monitored and optimized to avoid more invasive and costly urological procedures. In stone-forming patients, long-term use of alkali medication reduced stone recurrence over five-fold and the necessity of stone treatment procedures by more than ten-fold(6). Outpatient measurements of [tm] are performed on CaOx SFs exclusively at Ochsner.
Materials & Methods
Patient Selection
Over a period of 7 years, more than 700 CaOx SFs were studied at the Ochsner Renal Stone Clinic (ORSC) in 1500, often consecutive, patient visits. All patients had urographic and/or other physical...