Hyperphosphatemia is prevalent among children with nephrotic syndrome and normal renal function.

The aim of the study was to analyze systematically our observation that children with severe nephrotic syndrome (NS) have hyperphosphatemia despite normal kidney function. Forty-seven children with NS and normal glomerular filtration rate (GFR) were studied [26 with steroid-sensitive nephrotic syndrome (SSNS) and 21 with persistent NS]. The plasma phosphate level was expressed as the number of standard deviations (SDs) from the mean levels in age- and gender-matched controls. In SSNS plasma phosphate concentration was elevated (+3.7+/-2.0 SDs) during relapse and normalized (-0.7+/-1.7 SDs) in remission. In persistent NS the phosphate level was +4.0+/-2.1 SDs. Patients with marked hyperphosphatemia (>4 SDs) were younger (p<0.001), had lower plasma albumin (p<0.001), and had higher urinary protein levels (p<0.05). Hyperphosphatemia did not correlate with GFR, plasma calcium, or urinary sodium levels. Children with persistent NS had decreased serum 25(OH)D(3) and insulin-like growth factor 1 (IGF-1) concentrations. Hyperphosphatemia is prevalent among children with persistent nephrotic syndrome and normal renal function, correlates with its severity, and may result from increased urinary IGF-1 wasting.