Urinary oxalate excretion in urolithiasis and nephrocalcinosis

AIMS To investigate urinary oxalate excretion in children with urolithiasis and/or nephrocalcinosis and to classify hyperoxaluria (HyOx). METHODS A total of 106 patients were screened. In those in whom the oxalate: creatinine ratio was increased, 24 hour urinary oxalate excretion was measured. Liver biopsy and/or genomic analysis was performed if primary hyperoxaluria (PH) was suspected. Stool specimens were examined forOxalobacter formigenes in HyOx not related to PH type 1 or 2 (PH1, PH2) and in controls. RESULTS A total of 21 patients screened had HyOx (>0.5 mmol/24 h per 1.73 m2); they were classified into five groups. Eleven had PH (PH1 in nine and neither PH1 nor PH2 in two). Six had secondary HyOx: two enteric and four dietary. Four could not be classified. Seven patients had concomitant hypercalciuria. Only one of 12 patients was colonised withO formigenes compared to six of 13 controls. CONCLUSIONS HyOx is an important risk factor for urolithiasis and nephrocalcinosis in children, and can coexist with hypercalciuria. A novel type of PH is proposed. Absence of O formigenes may contribute to HyOx not related to PH1.