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Serial measurements of GFR in infants using the continuous iothalamate infusion technique. Southwest Pediatric
M A Holliday1, D Heilbron, A al-Uzri
1University of California, San Francisco.
Insights
This preliminary study found no significant difference in growth or glomerular filtration rate (GFR) between infants with congenital renal insufficiency fed low protein versus control formulas. Further clinical trials are needed to confirm dietary protein effects.
Area of Science:
- Pediatric Nephrology
- Nutritional Science
Background:
- Infants with congenital renal insufficiency often require specialized nutritional management.
- Assessing the impact of dietary protein on renal function and growth in this population is crucial.
Purpose of the Study:
- To validate plasma clearance of iothalamate (CIo) as an estimate of glomerular filtration rate (GFR) in infants.
- To conduct a preliminary study on the feasibility of a clinical trial comparing low protein versus control formula effects on GFR and growth in infants with congenital renal insufficiency.
Main Methods:
- Validated CIo method against plasma clearance of inulin (CIn) for GFR estimation.
- Enrolled 24 infants with congenital renal insufficiency (CIo < 55 ml/min/1.73 m2) aged 8-18 months.
- Randomly assigned infants to low protein or control formula, measuring CIo at multiple time points.
Main Results:
- The CIo method accurately estimated GFR.
- Average absolute GFR increased from 5.3 to 7.6 ml/min over 10 months, with no significant difference in percent increase based on initial GFR severity.
- Adjusted for age and body size, GFR did not change; no significant differences in CIo or serum creatinine changes were observed between diet groups.
Conclusions:
- A larger, longer clinical trial is necessary to definitively evaluate the effect of dietary protein on GFR and growth in infants with congenital renal insufficiency.
- The preliminary study successfully validated a GFR measurement method and provided data to inform future trial design.
Abstract:
We undertook a preliminary study to determine if a clinical trial was feasible that would compare the effect of a low protein vs a control formula on GFR and growth in infants with congenital renal insufficiency (CIo < 55 ml/min/1.73 m2). In this report from the Infant Diet Protein Study, we describe validation of a method using the plasma clearance of iothalamate (CIo) as an estimate of glomerular filtration rate (GFR) and results of the preliminary study relating to renal function. The plasma CIo method was validated as an accurate estimate of GFR by showing it to be the same as the plasma clearance of inulin (CIn). In the preliminary study infants who qualified for the study were randomly assigned to a low protein or control formula and were followed from 8 to 18 months of age. CIo was measured at 8, 14 and 18 months of age in 21 of the infants and at 8 and 18 months of age in all twenty four infants that entered the study. Average absolute GFR in the 24 infants increased in the 10 month period from 5.3 +/- 2.7 to 7.6 +/- 4.5 ml/min. The percent increase in GFR was no different in infants whose GFR at 8 months of age was severely reduced from those whose GFR was only moderately reduced. When adjusted for age and body size, GFR did not change. Change in mean CIo or serum creatinine (SCr) from 8 to 18 months of age between the infants in each diet groups was not different. We conclude that a clinical trial enrolling more infants and extending the study period is necessary to evaluate dietary protein effect.