Assessment of retinol-binding protein excretion in normal children.
Retinol-binding protein (RBP) is a low molecular weight protein freely filtered at the glomerulus. The fractional tubular reabsorption of RBP is 99.97% and increased excretion is therefore a sensitive marker of tubular dysfunction. We obtained early-morning urine specimens from 151 well children, from newborn to 16 years of age. RBP was measured using an enzyme-linked immunosorbent assay, albumin by a radioimmunoassay and creatinine by a modified Jaffé reaction. Protein excretion was assessed by calculating the protein:creatinine ratio for early-morning urine samples. We found a fall in both RBP and albumin excretion with increasing age, particularly in the 1st year of life, with a much wider variation in values from the infants studied. The mean excretion of RBP for children aged 0-6 months [51.4 (0.6-4,719) micrograms/mmol] was significantly higher (P < 0.001) than the mean for children aged 6 months to 16-years [15.0 (3.8-60) micrograms/mmol]. It has been shown that measurement of tubular proteinuria using the RBP: creatinine ratio is useful in the assessment of children with renal disease and we propose a value two standard deviations above the geometric mean for the age of the patient as an upper limit of normal.
Department of Paediatric Nephrology, Children's Hospital, Ladywood, Birmingham, UK.
G C
GC
Smith
M H
MH
Winterborn
C M
CM
Taylor
N
N
Lawson
M
M
Guy
D000293:Adolescent; D000419:Albuminuria / Q000652:urine; D002648:Child; D002675:Child, Preschool; D003404:Creatinine / Q000652:urine; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D011863:Radioimmunoassay; D012016:Reference Values; D012177:Retinol-Binding Proteins / Q000652:urine*
D012177:Retinol-Binding Proteins; D003404:Creatinine