The resistive index is a marker of renal function, pathology, prognosis, and responsiveness to steroid therapy in chronic kidney disease patients

Abstract

To evaluate the significance of the renal resistive index (RI) as a noninvasive marker of renal histological damage and a prognostic indicator, we examined RI by Doppler ultrasonography in 202 chronic kidney disease (CKD) patients who underwent renal biopsy. RI increased as the CKD stage progressed and correlated with age, systolic blood pressure, estimated glomerular filtration rate (eGFR), and renal histological changes, including glomerulosclerosis, arteriolosclerosis, and tubulointerstitial damage. Prognostic evaluation with a median follow-up period of 38.5 months revealed that patients with RI ≥ 0.7 (high RI group, n = 39) had significantly poorer renal survival than those with RI < 0.65 (normal RI group, n = 120) and 0.65 ≤ RI < 0.7 (high-normal RI group, n = 43). The patients in the high-normal RI group showed good response to steroids. However, in the high RI group, steroid therapy did not significantly improve renal survival. Of the clinical indices studied, RI ≥ 0.7, hypertension, proteinuria, and low eGFR at diagnosis were independent risk factors for worsening renal dysfunction. In conclusion, RI in CKD patients was considered as a marker of renal function, histological damage, and renal prognosis, and a possible determinant of indication for steroids.

Figure 1

Changes in kidney sizes based on chronic kidney disease (CKD) stages. The renal length was significantly smaller in patients with CKD stage 5 than in those with CKD stage 1 or 2 (P < 0.01). However, in CKD stages 1 to 4, there was no clear association between the disease stage and kidney size. *P < 0.05 versus stage 1, ^† P < 0.05 versus stage 2.

Figure 2

The resistive index (RI) based on CKD stages. An ultrasonographic image of a healthy control with CKD stage 1 (a) and of a patient with end-stage renal disease (ESRD) with CKD stage 5 (b). RI increased with CKD progression (P < 0.001) (c). *P < 0.01 versus stage 1, ^† P < 0.01 versus stage 2, ^§ P < 0.01 versus stage 3.

Figure 3

The correlation between RI and renal function. RI showed a correlation with estimated glomerular filtration rate (eGFR) (r = −0.52, P < 0.01).

Figure 4

RI and histological damage scores. RI was correlated with glomerulosclerosis (GS), arteriolosclerosis (AS), and tubulointerstitial (TI) damage scores. The highest correlation was shown in TI lesions (r = 0.32, P < 0.01 for the GS score; r = 0.36, P < 0.01 for the AS score; and r = 0.43, P < 0.01 for the TI score).

Figure 5

Kaplan-Meier analysis for survival from the decline in renal function by RI at renal biopsy (n = 202). Patients with RI ≥ 0.70 (high RI group) showed significantly poorer prognosis than those with RI < 0.65 (normal RI group) (P < 0.0001) or with 0.65 ≤ RI < 0.70 (high-normal RI group) (P = 0.02). Renal survival in the normal and high-normal RI groups did not differ significantly (P = 0.06). The 3-year survival rates for the normal, high-normal, and high RI groups were 0.967, 0.843, and 0.646, respectively.

Figure 6

Kaplan-Meier analysis of patients with different levels of RI stratified by steroid administration. The patients in the high-normal RI group showed good response to steroids. However, in the high RI group, steroid therapy did not significantly improve renal survival. The 3-year renal survival rates with and without steroid therapy were 0.982 and 0.947, respectively, (P = 0.89) in the normal RI group; 0.957 and 0.682, respectively, (P = 0.02) in the high-normal RI group; and 0.600 and 0.684, respectively, (P = 0.54) in the high RI group.