MO113CALCULATED URINARY CALCIUM-OXALATE SATURATION (ßCAOX) IS NOT SPECIFICALLY ELEVATED IN PATIENTS WITH PRIMARY HYPEROXALURIA

Abstract

Abstract Background and Aims In the primary hyperoxalurias (PH; types 1-3) recurrent urolithiasis (UL) and/or progressive nephrocalcinosis (NC) are the clinical hallmarks. Three different enzyme defects lead to endogenous oxalate overproduction and to extremely elevated urinary oxalate excretion (UOx). Thus, it seems logical that urine is supersaturated for calcium-oxalate (CaOx). It was, hence, speculated that urinary CaOx saturation (ßCaOx), calculated by computed programs, is significantly higher as compared to that of patients with idiopathic CaOx stones. We now aimed to evaluate and calculate urinary ßCaOx in PH patients according to type, as well as in non-PH patients with UL or NC. Method The computed equilibrium program EQUIL2 was used for the calculation of ßCaOx. For this, 24 h urine specimen of 70 patients with non-PH NC (46 male, 24 female, median age 6.06 (range 0.3-31.4 years)), of 149 idiopathic CaOx UL (90/59 m/f, age 8.5 (0.1-68.6)), of 51 PH 1 patients (31/21, age 12.33 (0.8-63.8)), of 5 PH 2 patients (3/2, age 5.41 (4.3-12.9)) and of 14 PH 3 patients (8/6, age 8.5 (2.9-29.3)) were analyzed for all necessary components. All patients were in stable kidney function (eGFR > 45 ml/min). Results Uox was higher in the PH patients as compared to the non-PH UL or NC patients (p < 0.05). However, there was no statistical difference between the Uox in PH 1 vs PH 2 or PH 3 patients, although, a clear effect of B6 medication was visible in PH1 patients. Urinary calcium excretion was lower (not significant) in PH patients as compared to NC/UL. There was no difference in ßCaOx when PH were compared to non-PH patients and it mostly remained in the normal range. Conclusion Urine ßCaOx is similar in PH and non-PH stone formers. Therefore, calculation of ßCaOx using computed programs is not a reliable parameter to define the definitively extreme CaOx supersaturation of urine from PH patients. This miscalculation is related to a rather lowish urinary calcium excretion in PH as compared to other UL/NC patients. Therefore, we recommend not to use such programs to express the risk of recurrent stone disease or nephrocalcinosis in PH.