Relevance of Resistive Index Ultrasonographic Measurement in Renal Transplantation

Abstract

The usefulness of the ultrasonographic measurement of resistive index (RI) is not yet fully understood. To obtain a better definition of its relevance in renal disease we studied this parameter in a group of 212 renal transplant patients, aged between 15 and 55 years: 81 first grafts with an excellent renal function, 44 hypertensive patients, 30 type II diabetics, 29 cases of chronic graft dysfunction, 28 cases during an episode of acute rejection. RI was measured in three different renal vascular areas: prerenal, interlobar and cortical. A two-way analysis of variance showed a statistical significance for the site of RI sampling and the type of pathology. There was no interaction between the two variables studied (p = 0.30). Plasma creatinine levels, analyzed as covariate, showed a high statistical correlation with RI values (p = 0.0001). The mean RI of the 80 transplanted patients with normal creatinine plasma levels showed a remarkable homogeneity and a statistically significant progressive reduction of the values from the main renal artery to the interlobar and cortical vessels (p = 0.00001). In the other groups a greater dispersion of data was present. RI values significantly increased in hypertensive and diabetic patients (p = 0.05) but more in acute rejection (p = 0.0001) or chronic graft dysfunction (p = 0.01). In acute rejection and in chronic graft dysfunction the curve of RI values tended to become flat, while in hypertensive and diabetic patients the aspect of the curve became steeper. In conclusion, RI is a hemodynamic index that reflects the vascular status of the explored area and is not only the simple expression of reduction of the kidney functional units. The differences observed in the various kidney areas stress the importance of measuring this parameter at more than one vascular site. The increase in RI values on the kidney cortex vessels is likely to be an index of glomemlar hyperfiltration. If this hypothesis is true the measure of RI might be a reliable method for diagnosing in the kidney vascular damage, glomemlar hypertension and hypertrophy.

Color Doppler Ultrasound in Renal Transplant: Role of Resistive Index versus Renal Cortical Ratio in the Evaluation of Renal Transplant Diseases

“…However, the data concerning the value of color Doppler US in the diagnosis of parenchymatous renal allograft dysfunctions are controversial because these pathologies mainly present as glomerular-tubular damages as well as vascular lesions and because they often occur concomitantly [14, 15, 16]. RI values provide valid information on the vascular status in the explored area but not on the glomerular function and the specific pathology [6]. RI is furthermore influenced by the patient’s extra-renal factors such as hypertension, heart rate and shock.…”

“…The sensitivity of RI is generally considered elevated while the specificity is low and only partially related to levels of plasma creatinine or to a reduction in glomerular filtration rate [6, 7]. The poor specificity of RI is particularly evident in acute pathologies which require an early diagnosis so that appropriate treatment may be commenced with a minimum of delay.…”

“…Some authors have demonstrated that there is a decrease in RI values when measured from the renal artery to the cortical vessels [4, 6, 9, 10]. This decrease, calculated as the renal cortical ratio (RCR), reflects the vascular status of the explored area [6].…”

“…This decrease, calculated as the renal cortical ratio (RCR), reflects the vascular status of the explored area [6]. The RCR is defined as the variation in RI values expressed in percent.…”

“…The RCR is defined as the variation in RI values expressed in percent. It differs in normal and pathological patients and provides reliable information on vascular dysfunction and therefore indirectly on parenchymal damage [6, 11]. …”