How useful is an oral calcium load test for diagnosing recurrent calcium stone formers?

Hypercalciuria is the main risk factor for recurrent calcium urolithiasis. The goal of our study is to determinate how useful an oral calcium load test is for stone formers to classify different forms of hypercalciuria in pathogenetic categories defined as renal or absorptive according to the current knowledge. Between June 2013 and February 2016, a prospective study was carried out on 117 documented recurrent hypercalciuric stone formers undergoing an oral calcium load test modified from the original description by Pak. After 2 days of calcium-restricted diet, urine and blood were analyzed at baseline and 120 min after receiving orally 1 g of calcium. Total and ionized calcium, parathyroid hormone from serum and urine calcium and creatinine were assessed in order to divide patients in three groups as previously described: resorptive, absorptive, and renal hypercalciuria. This allowed the identification of 19, 39, 34 and 33 patients with normocalcemic primary hyperparathyroidism (NPHPT), renal hypercalciuria aka renal calcium leak (RCL), absorptive hypercalciuria (AH) and unidentified cause, respectively. Patients with NPHPT (who required parathyroidectomy) experienced a lower PTH decrease (41.41 ± 12.82 vs. 54.06 ± 13.84% p < 0.01), higher beta-crosslaps, as well as lower TmP/GFR and distal third radius bone mineral density. RCL resulted in increased fasting urine calcium-to-creatinine ratio (Uca/Cr), i.e., > 0.37 mmol/mmol), without hyperparathyroidism. AH was diagnosed by the presence of ΔUCa/Cr > 0.60 mmol/mmol between baseline and 120 min without any other anomaly. For all remaining patients, results were inconclusive due to the lack of sufficient increase in serum calcium or because the cause of lithogenesis could not be clearly identified. The oral calcium load test is useful in nearly 80% of patients by identifying the different forms of hypercalciuria causing urolithiasis and by guiding treatment, including parathyroid surgery.

How the diagnosis and the management of genetic renal phosphate leak impact the life of kidney stone formers?

Genetic renal phosphate leak is one of the rare disorders in recurrent stone formers with absorptive hypercalciuria. Diagnosis and appropriate management may change the life of patients. To provide answers on how and when to make the diagnosis of genetic renal phosphate leak and how medical management prevents the recurrences and changes patients' life, we conducted a retrospective study including nine patients with recurrent nephrolithiasis and a confirmed genetic mutation of a phosphate transporter between 2008 and 2019 in our multidisciplinary center at the Pitié Salpetriere Hospital, Paris, France. We compared the number and the annual rate of urological intervention before and after the diagnosis and management using the Wilcoxon test. A qualitative survey was done to evaluate the quality of life of patients. A total of 9 patients were included in this study. Patient baseline characteristics and elements supporting the diagnosis are described. We showed an effective decrease in urological intervention number (p = 0.0078) and annual rate (p = 0.0117) after the diagnosis and the appropriate management, and an improvement in the patients' quality of life. The diagnosis and the appropriate management of genetic renal phosphate leak disorder improve the quality of life by preventing stone recurrence and decreasing the number of surgical intervention.