Renal threshold phosphate concentration (TmPO4/GFR).

Abstract

The ratio of maximum rate of renal tubular reabsorption of phosphate to glomerular filtration rate (TmPO4/GFR) was determined in 546 schoolchildren, aged between 6 and 17.9 years, using the nomogram of Walton and Bijvoet.1 TmPO4/GFR correlated with chronological age in girls and boys and in each remained significantly higher than in adults. TmPO4/GFR in the children correlated neither with fasting serum immunoreactive calcitonin and parathyroid hormone levels nor with the urinary cyclic AMP excretion. The study showed a parallel decrease in TmPO4/GFR, excretion of total hydroxyproline and serum alkaline phosphatase activities after puberty, with a significant relationship of both these indices of bone turnover to TmPO4/GFR values. This indicates that the high renal phosphate threshold of children may be an important factor for bone mineralisation by providing high extracellular inorganic phosphate concentrations during normal growth.