Relevance of the BONN Risk Index for metabolic monitoring of patients with calcium oxalate urolithiasis: a clinical application study of the Urolizer^®

The BONN Risk Index (BRI) successfully determines the calcium oxalate (CaOx) crystallization risk from urine samples. The BRI is based on a standardized crystallization test performed on native urine. A BRI-measuring device, the “Urolizer^®”, has been developed, operating automatically and requiring only a minimum of preparative efforts. In this study, the Urolizer^® is evaluated regarding its analytical and diagnostic practicability for metaphylaxis control in the framework of the daily routine of a stone surgery. From 51 CaOx recurrent stone-formers, 24 h urines were collected at the beginning and after 3 months of metaphylaxis. As much as 27 patients were indicated to suffer from “mild hypercalciuria”, low urinary pH or hypocitraturia, and 24 patients from “hypercalciuria”. The former were treated with alkaline citrate (AC), and the latter with hydrochlorothiazide (HCT). Analyses of urines collected before and during treatment, BRI using the Urolizer^®, and urinalysis-based risk indices were evaluated. In both patient groups, BRI decreased significantly, while metaphylaxis (P<0.001) in the AC group decreased from 1.08 (±0.58) to 0.56 (±0.39) L⁻¹ and in the HCT-group from 3.30 (±1.15) to 1.60 (±0.52) L⁻¹. In most patients, urinary parameters changed as desired and related risk indices decreased appropriately. The clinical utility of the easy-to-determine BRI is demonstrated. By quantifying the “overall” therapy effect within 15 min, the innovative analysis device may be especially suited for practitioners specializing in urolithiasis treatment.