The significance of renal resistive index as a non-invasive marker in renal dysfunction

Abstract

Introduction: A major worldwide health problem, chronic kidney disease (CKD), is characterised by a progressive loss of renal function. The asymptomatic nature of CKD in its early stages increases the likelihood of development to later stages and delays detection. Prompt identification and suitable treatment measures, such as pharmacological and nutritional adjustments, can greatly impede the advancement of the illness and lessen its consequences. Within the field of medical diagnostics, imaging methods are essential for the identification, treatment and management of CKD. Because it is the most effective modality for diagnosis and is non-invasive, ultrasound imaging stands out among the others. A key method in renal imaging, grey-scale ultrasound imaging, produces two-dimensional images that are necessary for assessing renal architecture and identifying size differences. Furthermore, colour Doppler is used to demonstrate renal perfusion and to provide important information on renal vascularisation. In addition, Spectral Doppler analysis, used to measure the blood flow velocities within the renal arteries, evaluates hemodynamic parameters that are essential for a thorough assessment of CKD. When taken as a whole, these ultrasound imaging methods provide a comprehensive toolset for the timely identification and efficient treatment of CKD, highlighting their vital significance in modern nephrology. Purpose: The purpose of the thesis was to report the findings of Doppler ultrasound studies of the renal resistive indices of patients who present with renal dysfunction, according to biochemical results at an academic hospital in Johannesburg, South Africa. This was to address the current knowledge gap surrounding the routinely requested Doppler renal ultrasound studies. Methods: A cross-sectional study of 100 patients presenting with renal dysfunction, as determined by biochemical markers, was carried out. These patients were referred for a renal Doppler ultrasound examination by the nephrology clinic. The study was carried out during the period of December 2022 and February 2023. All participants involved in the study provided informed consent prior to their participation. The study was conducted in adherence to ethical principles to ensure the integrity and ethical compliance of the research process. The ultrasound component of the investigation used a Siemens Acuson Redwood ultrasound machine to carry out the renal ultrasound examinations, and involved using a 3.5 MHz curvilinear probe to image in grey-scale, colour Doppler and spectral Doppler modes. The biochemical markers used in the study were GFR_MDRD, GFR-EPI, urea and creatinine. All of the above contributed to the independent variables of this study. The dependent variables of this study included the kidney sizes, echogenicity of the kidneys, the renal resistive index (RRI) and other pathology noted during the ultrasound examination. Data were analysed by a statistician of the Cape Peninsula University of Technology using SPSS version 28. Descriptive analysis, Spearman’s correlation analysis and inferential statistical analysis, Generalised linear models (GLMs), were used to test the relationship between independent variables and dependant variables. Results: There were one hundred (n = 100) participants, ages ranging from 18 to 90 years, comprising 52% females and 48% males with clinical indications of chronic kidney disease (50%), acute kidney injury (AKI) (20%), diabetes mellitus (10%), renal dysfunction (10%) and nephropathy (10%). Correlation results of ultrasound findings and biochemical results of the study showed that, presence of an elevated RRI (> 0.7) is a distinctive trait seen across a broad spectrum of participants with renal dysfunction rather than being restricted to a particular age. A raised RRI seen in the ultrasound results was not necessarily linked to the clinical indications. The biochemical markers GFR-MDRD, GFR EPI and urea were not linked to kidney size with p-values of 0.242, 0.319 and 0.649, respectively, when their levels indicated renal dysfunction. The study results demonstrated that kidney echogenicity, as opposed to ultrasound parameters such as kidney size and cortical thickness, was a more sensitive method of evaluating renal dysfunction in patients. Spearman’s correlation analysis showed a weak negative correlation between renal resistive index and GFR_MDRD and GFR-EPI (r = -0.104 and -0.102 for right and left kidney, respectively) and a weak positive correlation between the RRI and urea (r = 0.073 and 0.010 for right and left kidney, respectively) and creatinine (r = 0.111 and 0.017 for right and left kidney, respectively). Conclusion: Notably, all individuals diagnosed with renal dysfunction (n = 100) exhibited a raised RRI. These findings suggest that an elevated RRI may serve as a reliable marker for renal dysfunction. Further research is warranted to explore the underlying mechanisms of the