Biochemical risk factors for stone formation in a Scottish paediatric hospital population

Abstract

Renal stones in children, although rare, may be associated with morbidity and renal damage. Scottish children have a different ethnic composition and diet compared with paediatric populations previously studied. Urinary stone promoters include calcium, oxalate and urate. Postulated inhibitors include citrate and glycosaminoglycans (GAGs). We tested the hypothesis that Scottish paediatric stone-formers have higher excretion of urinary stone promoters (calcium/oxalate/urate) and/or lower excretion of stone inhibitors (citrate/GAGs) than children with isolated haematuria and controls. In this case-controlled study, we measured creatinine, calcium, oxalate, urate, citrate and GAGs in random urine samples from 24 stone-formers (excluding inherited metabolic disorders), median age 10.2 (range 1.0-17.2) y; 25 patients with isolated haematuria, 6.3 (0.6-13.7) y; and 32 controls, 7.5 (0.8-14.7) y. Excretion of urinary promoters and inhibitors differed among stone-formers, haematuria and control groups for (median (range)): calcium (0.82 (0.02-2.19), 0.43 (0.08-2.65), 0.31 (0.04-2.12) mmol/mmol creatinine, respectively, P = 0.005), citrate (0.42 (0.13-0.72), 0.33 (0.05-0.84), 0.61 (0.11-1.75) mmol/mmol creatinine, P = 0.001), calcium:citrate ratio (1.68 (0.19-4.81), 1.30 (0.19-9.57), 0.54 (0.10-2.27) mmol/mmol, P < 0.0001) and the promoter:inhibitor ratio (calcium x oxalate)/(citrate x GAGs) (8.3 (1.0-82.5), 4.3 (1.2-69.5), 2.8 (0.3-13.2) mmol/g, P < 0.0001). Scottish paediatric stone-formers had lower urinary citrate excretion and higher urinary calcium excretion, calcium:citrate ratio and promoter:inhibitor ratio compared with controls. Urinary calcium excretion and promoter:inhibitor ratio was also higher than children with isolated haematuria. Nevertheless, marked overlap between the stone-former and haematuria groups for promoter:inhibitor and calcium:citrate ratios suggests that some patients with isolated haematuria may be at future risk of urolithiasis.