Urinary microalbumin and retinol-binding protein assay for verifying children's nephron development and maturation

In order to further understanding of the development and maturation of the renal tubular reabsorption and glomerular permeability functions for the determination of the clinical pathological manifestation and treatment processing of renal diseases, random urine samples were collected from healthy subjects aged from birth to 60 years. All the samples were stored frozen at -70 degrees C for 4 months. The concentrations of the retinol-binding protein (RBP) and microalbumin (MALB) in urine were measured by enzyme-linked immunosorbent assay and at 492 nm with the microplate reader as a valuable marker of renal tubular and glomerular development and maturation The concentrations of RBP and MALB in urine gradually decrease with age. The level of RBP in urine is higher in children before 3 years than after 3 years (P < 0.01). The levels of MALB in urine is higher in children before 1 year of age than after 1 year (P < 0.01). Our results suggest that the development and maturation of the glomerular permeability functions and the renal tubular reabsorption are gradual and continuous processes from birth to adolescence but the key stage of their maturation may be at about 1 year and 3 years respectively: and that the rate of the tubular development may be slower than that of the glomerular development. Our results also extend existing data for normal ranges of RBP and MALB in urine from neonates to adults.