Estimation of Kidney Size From Foot Length in Newborns: A Cross-Sectional Study

Background Kidney size determination and sonographic follow-up are important in clinical diagnosis and treatment in children. Various anthropometric measurements are correlated with gestational age and birth weight and are used to identify high-risk babies in need of early interventions. Although foot length has emerged as a simple and reliable anthropometric measurement, it is not correlated with kidney size, except in the fetal period. This study was undertaken to find a correlation between foot length and kidney dimensions and estimate kidney size by finding regression equations in newborns. Methods We conducted a cross-sectional study and 216 newborns were enrolled at a tertiary care hospital. Foot length was measured by digital Vernier calipers and kidney dimensions were measured by ultrasonography. The Pearson correlation coefficient and simple linear regression tests were used to determine the relationship between foot length and kidney dimensions. Results Foot lengths and kidney dimensions were comparable in males and females as well as on the right and left sides, except for kidney length, which was found to be longer in males. Both right and left foot lengths showed highly significant (p<0.001) but small, positive correlations with corresponding side kidney length, breadth, and area, with R-values ranging from 0.2874 to 0.3668. However, the correlation between birth weight and foot length was significant, positive, and moderate (r=0.6962 and 0.6923 for right and left foot lengths, respectively). The regression equation for estimation of kidney size from foot length was obtained but the variance explained was small (e.g. R²=0.1325 for right kidney length). Out of 216 babies in our study, 10 babies had a renal anomaly. Conclusions We found a significant but small, positive correlation between foot length and kidney dimensions. Only 13.25% of the variance in kidney length was associated with foot length. Birth weight also had a significant and positive but small correlation with kidney dimensions. However, the correlation of birth weight with foot length was moderate, and a 57.14% variance in foot length was associated with birth weight. Multivariate regression analysis with more anthropometric parameters and gestational age may help in finding a better estimation of kidney size.