Markers of bone metabolism in children with nephrotic syndrome treated with corticosteroids.

The aim of the study was to assess bone mineral density, bone metabolism markers, and vitamin D level in children with idiopathic nephrotic syndrome in the course of 1-year observation. Twenty five children with nephrotic syndrome aged 5-17 years were enrolled into the study. The median number of relapses was 6 (range 1-22). All patients were treated with prednisone and vitamin D (800 IU/day). Bone mineral density of total body (TB-BMD) and lumbar spine (L-BMD), evaluated by dual energy X-ray absorptiometry (DXA) expressed as Z-score, and serum calcium, phosphorus, parathormone (iPTH), alkaline phosphatase (ALP), bone alkaline phosphatase (BAP), osteocalcin (OC), albumin, creatinine, 25(OH)D3, 1,25(OH)2D3 and urine calcium/creatinine ratio (uCa/Cr) were evaluated at the enrollment visit and after 1 year of therapy. After 1 year significant decreases of TB-BMD Z-score (from -0.24±1.34 to -0.74±1.31, p<0.05) and 25(OH)D3 serum level (from 31.7±16.3 to 23.7±9.3; p<0.05) were observed. No other appreciable differences were found. At the study onset, negative correlations were found between L-BMD Z-score and serum ALP, BAP, and phosphorus and between TB-BMD Z-score and urine uCa/Cr. After 1 year, L-BMD Z-score correlated negatively with serum BAP and OC, and positively with serum 25(OH)D3. Multivariate analysis showed that BAP was the strongest predictor of L-BMD Z-score (beta=-0.49; p<0.05). We conclude that children with nephrotic syndrome treated with corticosteroids are at risk of bone mass loss. Serum BAP concentration seems to be a good indicator of spongy bone metabolism in these children, who should be supplemented with vitamin D in an adjustable dose, possibly higher than 800 IU/24 h to prevent osteopenia.