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Expressing glomerular filtration rate in children
D C Heilbron1, M A Holliday, A al-Dahwi
1Department of Epidemiology and Biostatistics, University of California, San Francisco 94143-0704.
Insights
New standards for glomerular filtration rate (GFR) in children are proposed. Expressing GFR as a percentage of normal for age and weight improves comparisons, especially for infants.
Area of Science:
- Pediatric Nephrology
- Renal Physiology
- Biostatistics
Background:
- Current glomerular filtration rate (GFR) reference standards for children are adjusted to adult body surface area, complicating comparisons for infants.
- Existing GFR standards lack a smooth age-dependent variation, hindering accurate assessment in developing children.
- Difficulty in comparing observed GFR to reference values in children under one year of age.
Purpose of the Study:
- To develop a new method for estimating and presenting glomerular filtration rate (GFR) reference values in children.
- To establish age- and weight-adjusted GFR standards for improved clinical assessment in pediatric populations.
- To facilitate better comparison of GFR measurements across different age groups, particularly in infants.
Main Methods:
- Analysis of absolute GFR values from published studies in normal children.
- Development of an equation to estimate average GFR based on weight and term-adjusted age.
- Transformation of GFR data to a percentage of normal (% nl) relative to age and weight.
Main Results:
- An equation was derived to estimate average GFR from -2 months to 12 years, considering weight and term-adjusted age.
- GFR expressed as % nl for age and weight allows for approximate lower limits of normal to be defined.
- This % nl standardization enables combining GFR data from diverse pediatric age groups for analysis.
Conclusions:
- GFR expressed as a percentage of normal for age and weight offers a more appropriate standardization for children.
- This method facilitates serial GFR monitoring and comparison of results across different pediatric age groups.
- Absolute GFR values remain useful for patients with significant body mass distortion or very low GFR.
Abstract:
We have reviewed the studies that provide the current standards of reference for glomerular filtration rate (GFR) in normal children from 14 days to 12 years of postnatal age. These standards currently are presented as ml/min per 1.73 m2, i.e., adjusted to average adult body surface area. Children from birth to 1 year of age have adjusted values below the adult range, making comparisons of observed to reference values difficult. Currently, there is no accepted way of obtaining reference values that vary smoothly with age. An analysis of the absolute GFR values in normal children taken from published studies led to an equation that estimates average GFR in relation to weight and term-adjusted age from -2 months (7 months gestational age) to 12 years in children at least 14 days post delivery. When these data are transformed to percentage of normal (% nl) for age and weight (i.e., percentage of the estimated average), it is possible to describe approximate apparent lower limits of normal GFR as is now done for adults and older children. For children with loss of renal mass, GFR expressed as % nl for age and weight provides a convenient standardization which has several useful applications. First, results expressed as % nl for children of different ages, particularly under 1 year of age, can be combined with those of older children for summary purposes. Second, the course of GFR measured serially in children is more appropriately described using this method for expressing GFR. Reporting GFR in absolute values is also useful, particularly in patients whose body mass is significantly distorted or whose absolute GFR is low.