Hyperphosphaturia and hypermagnesuria in children with IDDM.

Urinary excretion of calcium, inorganic phosphorus, magnesium, glucose, and creatinine was measured in first-void spot urine samples collected 4 days apart in 220 insulin-dependent diabetic (IDDM) children (mean age 11.9 yr) attending a summer camp. A single control urine sample was obtained from 33 healthy nondiabetic siblings (mean age 11.2 yr). Mean +/- SD urinary calcium-creatinine ratios (UCa/Cr) did not significantly differ between IDDM and control subjects (0.14 +/- 0.09 vs. 0.12 +/- 0.09, respectively, P = 0.156). Mean urinary magnesium-creatinine ratios (UMg/Cr) were elevated in IDDM compared with control subjects (0.15 +/- 0.06 vs. 0.08 +/- 0.03, respectively, P = 0.0001). Similarly, mean urinary phosphorus-creatinine ratios (UP/Cr) were significantly increased over those in control subjects (1.12 +/- 0.33 vs. 0.40 +/- 0.22, respectively, P = 0.0001). UCa/Cr, UMg/Cr, and UP/Cr were correlated with increasing mean urine glucose content (P = 0.0001). No correlations were found when UCa/Cr, UMg/Cr, or UP/Cr were compared with patient age, duration of diabetes, glycosylated hemoglobin, or insulin dosage. Urine losses of phosphorus and magnesium were present even when glycemic control was considered good by several methods (glycosylated hemoglobin, short-term glycemic index, or urinary glucose content). Glomerular hyperfiltration was unable to account for increased urinary mineral content. In conclusion, the data indicate that urinary excretion of phosphorus and magnesium is elevated in children with IDDM, regardless of glycemic control. In the presence of glucosuria, this loss is further enhanced. Urinary calcium excretion is significantly higher only during periods of glucosuria. The data suggest that children with IDDM could be at risk for mineral deficiencies in the absence of intensive insulin management.