Role of intrarenal resistive index and ElastPQ® renal shear modulus in early diagnosis and follow-up of diabetic nephropathy: A prospective study

Abstract

Introduction: We aimed to establish baseline normal values of ElastPQ^® (Philips Healthcare, Bothell, Washington, USA) renal shear modulus, evaluate changes in intrarenal resistive index and renal shear modulus in various stages of diabetic nephropathy, their diagnostic potential and role in follow-up.

Methods: Our prospective observational study was performed over two years. In total, 130 adult cases with diabetic nephropathy and 130 normal adult controls were selected. Diabetic nephropathy was confirmed by persistent albuminuria on 24-hour urinary albumin testing at three month intervals and staged by albuminuria quantification. Measurement of intrarenal resistive index and renal shear modulus in all subjects was performed and their variation with stage of nephropathy was statistically analyzed using Pearson's correlation. Receiver operating characteristic curves were plotted and their individual and combined diagnostic potentials were assessed. Statistical significance was tested using t tests and analysis of variance. Interrater agreement was tested using Cohen's kappa coefficient.

Results: Mean intrarenal resistive index was significantly higher for cases (mean 0.72 ± 0.05) than controls (mean 0.62 ± 0.04) and showed significant age variation (p < 0.05). Normal values of ElastPQ^® renal shear modulus ranged from 3.87 to 4.72 kPa and was significantly higher for cases (mean 8.59 ± 1.77 kPa) than controls (mean 4.32 ± 0.45 kPa) and showed significant differences between each stage of nephropathy, being highest in stage 2. Maximum diagnostic accuracy was at 0.65 (sensitivity 90%, specificity 76.2%, area under curve 0.916) for intrarenal resistive index and at 5.31 kPa (sensitivity 90.8%, specificity 84.6%, area under curve 0.923) for renal shear modulus. Combination of the two further improved diagnostic performance (highest accuracy of 89%, sensitivity 81.7%, specificity 96.3%).

Conclusions: Normal range of ElastPQ^® renal shear modulus values could be established. Intrarenal resistive index and renal shear modulus can be used as imaging parameters for early diagnosis and follow-up of diabetic nephropathy.

Keywords: Diabetic nephropathy; ElastPQ®; renal Doppler; renal elastography; renal shear modulus.

Figure 1.

Forty-two-year-old non-diabetic woman with normal kidneys. Renal cortical echotexture appears normal. Renal Doppler (left) shows intrarenal resistive index of 0.57. ElastPQ^® shear wave elastography (right) shows renal shear modulus of 4.27 kPa.

Figure 2.

Forty-eight-year-old diabetic man with stage II diabetic nephropathy. Renal cortical echotexture appears normal. Renal Doppler (left) shows intrarenal resistive index of 0.69 (elevated). ElastPQ^® shear wave elastography (right) shows renal shear modulus of 11.60 kPa (significantly elevated).

Figure 3.

Fifty-three-year-old diabetic woman with stage V diabetic nephropathy. Renal cortical echogenicity appears raised. Renal Doppler (left) shows intrarenal resistive index of 0.77 (significantly elevated). ElastPQ^® shear wave elastography (right) shows renal shear modulus of 5.29 kPa (mildly elevated).

Figure 4.

ROC curve for intrarenal resistive index between controls and cases of diabetic nephropathy. AUC: area under curve; ROC: receiver operating characteristic.

Figure 5.

ROC curve for renal shear modulus between controls and cases of diabetic nephropathy. AUC: area under curve; ROC: receiver operating characteristic.