Relationship between renal dimensions using ultrasonography and body mass index in apparently healthy school children in Port Harcourt, Nigeria

Background: Renal size is an important parameter in evaluation and management of a child with kidney disease. Establishing the normal limits of renal sizes standardized against somatometric parameters will be a useful tool in detecting probable renal diseases in children. Aim: To determine renal sizes in relation to body mass index (BMI) in apparently healthy primary school children in Port Harcourt. Materials and Methods: This was a cross-sectional and multi-staged study involving 450 children aged 6-12 years. Renal ultrasonography was carried out using a portable DP 1100 PLUS real time ultrasound machine fitted with 3.5MHz probe. The length, width and anteroposterior diameter of the kidneys were measured, and renal volume calculated. The BMI percentile for age and sex were obtained. The renal sizes were correlated with somatometric parameters and regression equations derived. Results: The mean renal length and volume percentiles increased from 77.7 ± 5.6 and 49.2 ± 13.7 at 6years to 85.9 ± 5.9 and 60.4 ± 18.4 at 12years respectively. There were no significant differences in the length and volume between the right and left kidneys, and dimensions of the kidneys were not statistically different in males and females. There was a significant positive correlation between BMI and renal dimensions. The renal length and volume increased at a rate of 1.372mm and 1.951cm3 per year and at a rate of 0.067mm and 0.176cm3 per one percentile increase in BMI respectively. The regression model derived for predicting renal length in mm =65.731 + (1.372 Age X) + (0.067 BMI percentile X) while that for renal volume in cm3 =26.386 + (1.951 Age X) + (0.176 BMI percentile X), (Where X is the independent variables: age in years and BMI in percentile). Conclusion: BMI has a significant positive linear relationship with renal dimensions. This study has provided prediction models for deriving renal length and volume from subject's BMI and age.