Assessment of retinol-binding protein excretion in normal children |
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Authors: | Graham C Smith Michael H Winterborn Christopher M Taylor Nigel Lawson Mark Guy |
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Institution: | (1) Department of Paediatric Nephrology, The Children's Hospital, Ladywood, B16 8ET Birmingham, UK;(2) Department of Clinical Chemistry, East Birmingham Hospital, Bordesley Green East, Birmingham, UK;(3) Present address: Department of Paediatric Nephrology, Royal Hospital for Sick Children, Yorkhill, G3 8SJ Glasgow, Scotland |
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Abstract: | 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) g/mmol] was significantly higher (P<0.001) than the mean for children aged 6 months to 16-years 15.0 (3.8–60) g/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. |
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Keywords: | Retinol-binding protein Albumin Early morning urine Tubular proteinuria Renal disease assessment |
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