The influence of kidney depth measured by computed tomography on glomerular filtration rate in patients with moderate and severe obstructive nephropathy

Purpose: This study aimed to evaluate the effect of CT for correcting the renal depth on the accuracy of GFR in the patients with moderate and severe hydronephrosis. Methods: Fifty five patients with hydronephrosis were studied. All the subjects were accepted the diuretic dynamic renal imaging, injected 99mTc-DTPA, and abdominal CT scanning after renal imaging. GFR in all patients were tested by two-sample plasma clearance method. The tønnesen's formula and CT were used to measure the kidney depths.According to tGFR, all the subjects were divided into 3 groups: (1)patients: GFR≥90 ml/min1.73m2; (2)patients: 60≤GFR＜90 ml/min1.73m2; (3)patients: 0＜GFR＜60 ml/min1.73m2. All statistical analysis was done with SPSS statistics version 25.0. Results: In patients with moderate to severe hydronephrosis, the renal depths in normal and hydronephrotic kidneys measured by CT were significantly greater compared to Tønnesen formula(t=-6.61, t=-9.65, p＜0.05, p＜0.05). 2. In GFR ≥90 ml/min1.73m2 and 60≤GFR＜90 ml/min1.73m2 groups, significant differences between gGFR and tGFR weren’t found , and dGFR was significantly higher than tGFR (t=-2.779, t=2.62, p=0.013, p=0.01). In GFR＜60 ml/min1.73m2 group, significant differences between tGFR and all other GFRs were noted (t = 2.68, t = -4.33, p < 0.05, p < 0.05). 3. In the patients with moderate to severe hydronephrosis, there were statistically differences between dGFRsingle and gGFRsingle in normal and hydronephrotic kidneys (t=7.46, t=6.16, p<0.05, p<0.05). Conclusion: The CT-based renal depth-calibrated GFR could be more accurately used to evaluate the renal function in the patients with moderate-to-severe hydronephrosis. Key words: hydronephrosis; glomerular filtration rate; computed tomography; Gates method; kidney depth