Plasma oxalate level in pediatric calcium stone formers with or without secondary hyperoxaluria

Plasma oxalate (POx) concentration is significantly elevated in primary hyperoxaluria, severe renal failure or ethylene glycol poisoning. In these conditions, the degree of hyperoxalemia correlates with the severity of systemic calcium oxalate (CaOx) deposition and should be therefore carefully monitored. Although secondary hyperoxaluria (secHyOx) is a common finding in pediatric patients with kidney stone disease, very little is known about POx in this condition. We therefore evaluated POx level in 59 children and adolescence with calcium urolithiasis (34 confirmed by CaOx stone analysis and 25 children with a strong clinical suspicion of this type of urolithiasis), with or without “mild” secHyOx. A control group consisted of 41 healthy sex- and age-matched children. We found that POx was significantly increased in children with calcium urolithiasis and secHyOx compared to healthy children (9.16 ± 3.60 vs. 6.42 ± 2.53 μmol/l), but that was not the case in children with calcium urolithiasis but with normal urinary oxalate excretion (7.12 ± 3.33 μmol/l). We conclude that POx may be slightly increased in some pediatric calcium stone formers with secHyOx, probably related to intestinal oxalate hyperabsorption.