### INTRODUCTION

### MATERIALS AND METHODS

### Patient selection and data extraction

##### Table 1

### Measurement of renal size

### Statistical procedures

##### Table 2

##### Table 3

##### Table 4

^{2}) and the standardized coefficients or beta coefficients (β) were calculated from the statistical analyses. The R

^{2}indicates how well the data fit a statistical model (a line or a curve). In each step, R

^{2}is increased after a new variable is added. Change in R

^{2}is considered significant if the significance of change in F (ΔF) is less than 0.05. The standardized coefficients is the estimate from standardized regression analysis so that the variances of dependent and independent variables are 1; it is used to compare the influence of each variable. The variance inflation factor (VIF) is used to assess collinearity; if VIF is 10 or greater, collinearity is high.

^{2}. The equation has the following form:

_{1}, X

_{2}, …, X

_{n}are the independent variables (i.e., age, weight, height, BSA), and b

_{0}is the constant where the regression line intercepts the Y axis when all the independent variables are 0. The equation can be used to investigate which variables influence the dependent variable, and to estimate the dependent variable (i.e., the renal length or volume) when other variables are known. Linear regression analysis was also used to draw a scatter plot to estimate renal length and volume from anthropometric parameters. Results were considered statistically significant if the

*P*value was < 0.05 for all data analyses.

### RESULTS

### Patient characteristics

^{3}. Paired t-tests indicated that the length of the left kidney was significantly greater than that of the right kidney (8.93 ± 1.36 cm vs. 8.59 ± 1.28 cm;

*P*< 0.001). In another paired t-test, the left renal volume was also significantly greater than the right renal volume (102.89 ± 42.70 cm

^{3}vs. 92.99 ± 37.94 cm

^{3};

*P*< 0.001; Table 1). There was no difference in renal size according to sex (Tables 2 and 3).

### Mean renal length according to height

### Renal size estimated by univariate linear regression analysis

^{3}per year.

^{3}):

*P*< 0.001). Fig. 1 shows the correlations of all parameters as a scatter plot, and the line of best fit for the relationship. The height and age of the patients showed the strongest correlation with the lengths of both right (R

^{2}= 0.68;

*P*< 0.001) and left (R

^{2}= 0.69;

*P*< 0.001) kidneys. Furthermore, the volume of both right (R

^{2}= 0.78;

*P*< 0.001) and left (R

^{2}= 0.78;

*P*< 0.001) kidneys showed the strongest correlation with BSA.

##### Table 5

### Renal size estimated by multivariate analysis

^{2}, β, ΔF, VIF, and F value, as well as

*P*value was obtained.

##### Table 6

*P*< 0.001). When age was added in step 2, significant increase was observed in R

^{2}(ΔF = 15.57;

*P*< 0.001). However, VIF was so large (VIF = 10.23) that it was considered inappropriate to implement the equation of step 2 (Table 6). Height was also the only significant of the 3 variables (weight, height, and BSA) in a stepwise multiple regression analysis without age, which had a large VIF.

^{2}= 0.70;

*P*< 0.001). The change in F was also significant (

*P*< 0.001). The influence of height on left renal length was larger than that of weight (β = 0.66 vs. β = 0.19).

^{2}= 0.79;

*P*< 0.001). The change in F was also significant (

*P*= 0.039). Their VIF was less than 10 (VIF = 7.66). BSA correlated more strongly with right renal volume than did age (β = 0.73 vs. β = 0.16).

^{2}= 0.78;

*P*< 0.001).

### DISCUSSION

^{2}on univariate regression analysis for renal length. BSA had the strongest relationship with renal volume on univariate regression analysis.

^{2}of all independent variables tends to increase when the renal volume, rather than length, is used to measure renal size (Table 5). Additionally, BSA was the most significant factor, among the various body indices, for estimating renal volume. Therefore, when measuring and estimating renal size, it is more accurate to use renal volume and BSA than renal length and other body indices. This is similar to previous findings that showed BSA to be a good indicator of renal size (72627).