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Renal length and inulin clearance in the radiologically normal single kidney
Bridget E Wilson1, Paul Davies, Kishore Shah
1Department of Nephrology, Birmingham Children's Hospital, Steelhouse Lane, B4 6NH, Birmingham, UK.
Insights
Children with a single functioning kidney show compensatory hypertrophy. Larger single kidneys correlate with higher glomerular filtration rates, suggesting potentially elevated single nephron filtration in these children.
Area of Science:
- Pediatric Nephrology
- Renal Physiology
- Developmental Biology
Background:
- Compensatory hypertrophy of a single kidney is recognized, even in utero.
- Long-term consequences of hypertrophy and hyperfiltration in single kidneys remain unclear.
- Understanding pediatric single kidney growth is crucial for assessing renal function.
Purpose of the Study:
- To define growth parameters for single kidneys in children.
- To correlate single kidney growth with inulin clearance (glomerular filtration rate).
- To investigate the relationship between renal size and function in children with a solitary functioning kidney.
Main Methods:
- Studied 74 children with a single functioning kidney from infancy.
- Collected simultaneous inulin clearance and renal length measurements at ages 5, 10, and 16.
- Utilized real-time ultrasound for renal length and continuous infusion for inulin clearance.
Main Results:
- Established nomograms for single kidney growth correlated with age, height, weight, and body surface area.
- Renal length showed the strongest correlation with body surface area (r=0.85, P<0.001).
- Inulin clearance per body surface area positively correlated with standardized renal length (r=0.53, P<0.001).
Conclusions:
- Larger single kidneys in children are associated with higher glomerular filtration rates.
- Single kidneys in these children are hypertrophied.
- The single nephron glomerular filtration rate is likely abnormally high in children with a solitary functioning kidney.
Abstract:
Compensatory hypertrophy of a single functioning kidney is well described and has been shown to occur in utero. The long-term effects of hypertrophy and hyperfiltration in this situation are unknown. This study defined the growth parameters for single kidneys during childhood and correlated them with inulin clearance. Patients were those who had a radiologically "normal" single kidney, where the contralateral kidney was known to be non-functioning from infancy. Data were obtained from 74 children (40 boys and 34 girls) drawn from a registry of cases with a single kidney, and in whom simultaneous measurements of inulin clearance and renal length had been made at around 5, 10, and 16 years of age. Renal length was taken as the maximal bipolar measurement using real-time ultrasound scan. Inulin clearance was by continuous infusion technique. Nomograms for single kidney growth were determined against age, height, weight, and body surface area. Renal growth was correlated with inulin clearance. Renal length was found to correlate best with body surface area ( r=0.85, P<0.001), but this was not significantly superior to correlations with age, height, or weight separately. Inulin clearance per body surface area correlated positively with standardized renal length, i.e., Z score for renal length normalized for body surface area ( r=0.53, P<0.001). The larger kidneys have a higher glomerular filtration rate. Provided that the nephron number in the single kidney is similar to that in a paired kidney, single kidneys are hypertrophied and the single nephron glomerular filtration rate is likely to be abnormally high in these children.