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Real-time Analyses of Retinol Transport by the Membrane Receptor of Plasma Retinol Binding Protein
Published on: January 28, 2013
Assessment of retinol-binding protein excretion in normal children
G C Smith1, M H Winterborn, C M Taylor
1Department of Paediatric Nephrology, Children's Hospital, Ladywood, Birmingham, UK.
Insights
Retinol-binding protein (RBP) excretion decreases with age in children, with significantly higher levels in infants under six months. This finding helps establish normal RBP:creatinine ratios for assessing pediatric kidney health.
Area of Science:
- Nephrology
- Pediatric Nephrology
- Clinical Chemistry
Background:
- Retinol-binding protein (RBP) is freely filtered by the glomerulus.
- Near-complete tubular reabsorption of RBP makes its excretion a sensitive indicator of tubular dysfunction.
- Assessing RBP excretion aids in evaluating pediatric renal health.
Purpose of the Study:
- To establish age-specific reference ranges for RBP excretion in healthy children.
- To investigate the relationship between RBP excretion and age in pediatric populations.
- To validate the RBP:creatinine ratio as a marker for tubular proteinuria in children.
Main Methods:
- Collected early-morning urine samples from 151 healthy children (newborn to 16 years).
- Measured RBP via ELISA, albumin via radioimmunoassay, and creatinine via modified Jaffé reaction.
- Calculated RBP:creatinine and albumin:creatinine ratios to assess protein excretion.
Main Results:
- RBP and albumin excretion decreased with age, most notably in the first year of life.
- Infants (0-6 months) showed significantly higher mean RBP excretion (51.4 µg/mmol) compared to older children (6 months-16 years, 15.0 µg/mmol).
- A wide variation in RBP excretion values was observed in infants.
Conclusions:
- The RBP:creatinine ratio is a valuable tool for assessing tubular proteinuria in children with renal disease.
- Proposed upper limit of normal for RBP:creatinine ratio is two standard deviations above the geometric mean for the patient's age.
- Age-specific reference ranges are crucial for accurate interpretation of RBP excretion in pediatric nephrology.
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) 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.
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