Renal reabsorption of phosphate in children with sickle cell anemia

It has previously been reported that in adult patients with sickle-cell ane mia the serum phosphate value and the maximum tubular reabsorption of phosp hate per liter of glomerular filtrate (TmP/GFR) were significantly higher t han in normal controls. This does not appear to have been studied in childr en with sickle cell anemia (young sicklers) and this prompted us to assess renal phosphate reabsorption in this group of patients. We looked at serum phosphate level and calculated renal phosphate reabsorption (TP/GFR) in chi ldren taking random urine and blood samples at the same time and using the formula TP/GFR = Sp - Up x SCr: UCr, in 30 young sicklers all of whom had n ormal renal function (mean age 7.3 years) and 40 normal matching controls ( mean age 6.5 years). The mean serum phosphate value in young sicklers was s ignificantly lower than in controls (4.3 against 5.3 mg/dl) while the mean value of TP/GFR was 4.09 +/- 0.74 mg/dl in young sicklers compared to 4.65 +/- 0.75 mg/dl in the control group (p = 0.0026). Therefore, the TP/GFR in young sicklers was also significantly lower (p = 0.0026) than in the contro l group. This may be explained by the high serum level of parathyroid hormo ne reported previously in patients with sickle cell anemia which is expecte d to lower phosphate reabsorption (TmP/GFR and TP/GFR are identical in chil dren). The lower serum phosphate value and TP/GFR in younger sicklers seems to be in contrast with the relatively high serum phosphate value and TP/GF R previously reported in adults with sickle cell anemia. Copyright (C) 1999 S. Karger AG, Basel.