## 3 Results  
A total of 51 patients, consisting of 21 males and 30 females with a mean age of 60.5 years (range 25-86 years), were enrolled in this study (Table 1). Among them, ten patients were diagnosed with comorbid diabetes mellitus. Clinical manifestations of these patients included hydronephrosis and renal calculus (\(n=32\), 62.7%), renal tumors (\(n=10\), 19.6%), urinary tract infection (\(n=2\), 3.9%), acute kidney injury (\(n=1\), 2.0%), and some other or undetermined diagnosis (\(n=6\), 11.8%). Plasma creatinine level ranged from 0.48 mg/dL to 6.12 mg/dL, and the mean value was 1.8 \(\pm\) 1.3 mg/dL. The average modified eGFR was 60.5 \(\pm\) 42.7 mL/min. The mean GFRs calculated by [PERSON]'s formula, [PERSON]'s formula, [PERSON]'s formula, and CT were 45.3 \(\pm\) 23.3, 54.7 \(\pm\) 27.5, 56.5 \(\pm\) 26.3, and 63.7 \(\pm\) 30.0, respectively.  
Figure 2: Demonstration of measuring the renal depth via CT image. Two axial slices including the middle of each kidney were collected. The point of deepest (D) and superficial (S) to back body surface were drawn. The renal depth was calculated as (D + S)/2.  
The scatter plot and regression lines are seen in Figure 3. The correlation coefficient of the calculated GFRs ([PERSON]'s, [PERSON]'s, [PERSON]'s, and CT) and modified eGFR were 0.87, 0.87, 0.87, and 0.84, respectively. All were statistically significant with a \(p\)-value \(<\) 0.001. The Bland-Altman plot showed good agreement between GFRs calculated by [PERSON]'s (\(p\) = 0.0001) and the modified eGFRs. However, no statistical difference was observed between the GFRs calculated by [PERSON]'s (\(p\) = 0.0818), [PERSON]'s (\(p\) = 0.2355) methods, and by a CT scan (\(p\) = 0.3402) and the modified eGFR (Figure 4).  
Figure 4: _Cont_.  
Figure 3: The correlation between GFRs calculated using renal depth by four ways and modified eGFR. (**A**), the GFR calculated using the renal depth estimated by [PERSON]’s formula (r = 0.87, y = 0.476x + 16.477). (**B**), the GFR calculated using the renal depth estimated by [PERSON]’s formula (r = 0.87, y = 0.560x + 20.879). (**C**), the GFR calculated using the renal depth estimated by [PERSON]’s formula (r = 0.87, y = 0.534x + 24.170). (**D**), the GFR calculated using the renal depth estimated by CT (r = 0.84, y = 0.589x + 28.101).  
The renal depth, when estimated by the three formulae, was significantly smaller than that estimated by a CT scan (all for \(p<0.05\)), and the right side was somewhat larger than the left side (\(p<0.05\); Figure 5). On the contrary, the deeper right renal depth was found only in 63% of the patients when estimated by CT scans. In patients with modified eGFR \(>60\) mL/min, the GFRs calculated using [PERSON]'s formula were obviously low, leading to the underestimation of the GFR in the clinical setting. The GFRs calculated using CT scans were closer when the modified eGFR was more than 60 mL/min (Figure 6).  
Figure 4: The Bland–Altman plot for GFRs calculated through four methods and the modified eGFR. (**A**), GFR calculated by [PERSON]’s formula (\(p=0.0001\)). (**B**), GFR calculated by [PERSON]’s formula (\(p=0.0818\)). (**C**), GFR calculated by [PERSON]’s formula (\(p=0.2355\)). (**D**), GFR calculated by CT scan (\(p=0.3402\)).  
Figure 5: The boxplots for comparison of the bilateral renal depth measured by three formulas ([PERSON]’s, [PERSON]’s, and [PERSON]’s) and the CT scan. (**A**), right renal depth. (**B**), left renal depth.  
Figure 6: The boxplots for comparison of the GFRs calculated by [PERSON]’s, [PERSON]’s, [PERSON]’s formula, CT scan, and the modified eGFR. (**A**), patients with modified eGFR more than 60 mL/min. (**B**), patients with modified eGFR less than 60 mL/min.