Renal Resistive Index: Revisited

Abstract

Introduction Chronic kidney disease (CKD) is universally considered a public health burden and the majority of cases are found to be diabetic at the time of diagnosis. Renal biopsy is the prime modality for the complete evaluation of renal injuries but is invasive. Duplex Doppler sonography can help to determine renal resistive index (RRI), which is an excellent marker for demonstrating dynamic or structural changes of intrarenal vessels. In this study, we evaluated the intrarenal hemodynamic abnormalities with RRI in diabetic and non-diabetic kidney disease patients. Also, RRI was correlated with the established parameters of renal dysfunction, i.e., estimated glomerular filtration rate (eGFR) and other biochemical parameters. Results There was a significant correlation of RRI with eGFR and serum creatinine indicating its role as a Doppler parameter, which can be used as complementary to biochemical parameters. A remarkable difference was noted in the RRI values between diabetic and non-diabetic groups in the early stages of CKD, revealing its ability to arrive at etiopathogenesis in the early stages. The renal resistive index increases in a sequential pattern and is an indicator of declining renal function. Conclusions The addition of sonographic parameters like renal resistive index could help in the complete evaluation of chronic kidney disease in diabetic and non-diabetic groups. A sequential increase in renal resistive index is a better indicator of the progressive worsening of renal function as opposed to an absolute cut-off value.

Keywords: chronic kidney disease; diabetic nephropathy; duplex doppler sonography; egfr; renal resistive index.

Figure 1. Scatter diagram illustrating the correlation of RRI and eGFR

RRI: renal resistive index; eGFR: estimated glomerular filtration rate

Figure 2. ROC curve to determine the cut-off of RRI

ROC: receiver operating characteristic; RRI: renal resistive index

Figure 3. 52-year-old diabetic male with stage IV CKD - average RRI = 0.73

RRI at each pole in the right kidney a) upper pole - 0.69, b) mid pole - 0.70, c) lower pole - 0.67. RRI at each pole in the left kidney d) upper pole - 0.75, e) mid pole - 0.72, f) lower pole - 0.86 RRI: renal resistive index

Figure 4. 34-year-old non-diabetic female with stage IV CKD - average RRI = 0.68

RRI at each pole in the right kidney a) upper pole - 0.71, b) mid pole - 0.68, c) lower pole - 0.65. RRI at each pole in the left kidney d) upper pole - 0.60, e) mid pole - 0.72, f) lower pole - 0.74 RRI: renal resistive index

Figure 5. 32-year-old diabetic female with stage V CKD - average RRI = 0.79

RRI at each pole in the right kidney a) upper pole - 0.74, b) mid pole - 0.81, c) lower pole - 0.88. RRI at each pole in the left kidney d) upper pole - 0.88, e) mid pole - 0.71, f) lower pole - 0.74 RRI: renal resistive index

Figure 6. 51-year old non-diabetic male with stage V CKD - average RRI = 0.78

RRI at each pole in the right kidney a) upper pole - 0.77, b) mid pole - 0.69, c) lower pole - 0.82. RRI at each pole in the left kidney d) upper pole - 0.83, e) mid pole - 0.80, f) lower pole - 0.82 RRI: renal resistive index