Early assessment of renal resistance index and long-term renal function in renal transplant recipients

Investigating the role of ultrasound-based shear wave elastography in kidney transplanted patients: correlation between non-invasive fibrosis detection, kidney dysfunction and biopsy results-a systematic review and meta-analysis

INTRODUCTION

Interstitial fibrosis and tubular atrophy are leading causes of renal allograft failure. Shear wave elastography could be a promising noninvasive method for providing information on the state of the kidney, with specific regard to fibrosis but currently available data in the literature are controversial. Our study aimed to analyze the correlation between shear wave elastography and various kidney dysfunction measures.

METHODS

This review was registered on PROSPERO (CRD42021283152). We systematically searched three major databases (MEDLINE, Embase, and CENTRAL) for articles concerning renal transplant recipients, shear wave elastography, fibrosis, and kidney dysfunction. Meta-analytical calculations for pooled Pearson and Spearman correlation coefficients (r) were interpreted with 95% confidence intervals (CIs). Heterogeneity was tested with Cochran's Q test. I2 statistic and 95% CI were reported as a measurement of between-study heterogeneity. Study quality was assessed with the QUADAS2 tool.

RESULTS

In total, 16 studies were included in our meta-analysis. Results showed a moderate correlation between kidney stiffness and interstitial fibrosis and tubular atrophy, graded according to BANFF classification, on biopsy findings for pooled Pearson (r = 0.48; CI: 0.20, 0.69; I2 = 84%) and Spearman correlations (r = 0.57; CI: 0.35, 0.72; I2 = 74%). When compared to kidney dysfunction parameters, we found a moderate correlation between shear wave elastography and resistive index (r = 0.34 CI: 0.13, 0.51; I2 = 67%) and between shear wave elastography and estimated Glomerular Filtration Rate (eGFR) (r = -0.65; CI: - 0.81, - 0.40; I2 = 73%). All our outcomes had marked heterogeneity.

CONCLUSION

Our results showed a moderate correlation between kidney stiffness measured by shear wave elastography and biopsy results. While noninvasive assessment of kidney fibrosis after transplantation is an important clinical goal, there is insufficient evidence to support the use of elastography over the performance of a kidney biopsy.

Association of renal resistive indices with kidney disease progression and mortality

BACKGROUND

Renal resistive indices (RRI) have been shown to predict the progression of kidney disease. This study aims to evaluate the association of RRI with mortality and dialysis initiation after adjustment to therapeutic and life style interventions.

METHODS

This is a retrospective study that included all chronic kidney disease patients followed for at least two years in three nephrology clinics between 2006 and 2019 and who had a RRI level in their files. Kaplan Meier and log rank test compared the survival of patients with normal versus high RRI. Cox regression analysis evaluated the association between RRI and death or dialysis initiation after adjustment to treatments and life style modifications.

RESULTS

A total of 192 patients were analyzed: 68 had RRI < 0.7 and 124 had RRI ≥ 0.7. Their mean age was 66.5 ± 13.1 years at first visit, 78.1% were males. There was a negative correlation between baseline eGFR and RRI (p < 0.001; Spearman correlation coefficient = -0.521). The survival was significantly better in patients with RRI < 0.7 with a Log Rank test < 0.001. The univariate cox regression analysis showed a significant association between RRI and mortality (HR = 1.08; 95%CI: 1.04-1.11; p < 0.001) that remained significant after adjustment to cardiovascular risk factors and interventions such as salt reduction, blood pressure control, statins and RAAS inhibitors (HR = 1.04; 95%CI: 1.00-1.08; p = 0.036). Cox regression analysis showed a significant association between RRI and dialysis initiation (HR = 1.06; 95%CI 1.01-1.10; p = 0.011).

CONCLUSION

Our study revealed that patients with an elevated RRI ≥ 0.7 are at a higher risk of mortality after adjustment to medications and lifestyle modifications. RRI can, according to this study, be considered as an independent prognostic factor in CKD patients.

Predictive value of the renal resistive index in the immediate postoperative period after kidney transplantation on short- and long-term graft and patient outcomes

INTRODUCTION

During the postoperative stay in the intensive care unit after kidney transplantation, the renal resistive index (RI) is routinely measured. An increased RI, measured months posttransplant, is associated with a higher mortality. We wanted to investigate the value of the RI immediately posttransplant in predicting both short- and long-term outcome.

METHODS

We performed a retrospective single-center study. The RI was collected <48 h posttransplant in patients undergoing kidney transplantations between 2005 and 2014. Short-term outcome was evaluated by delayed graft function (DGF). The long-term endpoints were kidney function and mortality at 30 days, 1 year and 5 years.

RESULTS

We included 478 recipients, 91.4% of whom reached the end of the 5-year follow-up. A higher RI < 48 h posttransplant was significantly associated with DGF. This association was particularly strong in patients receiving grafts from donors after brain death and expanded criteria donors. A higher RI also correlated with mortality and death with functioning graft but not with graft failure. After adjustment for confounders, we found an association between increased RI and DGF, but not with long-term kidney function or mortality.

CONCLUSION

The RI routinely measured <48 h posttransplant is an independent predictor of short-term kidney function.

The role of renal resistive index as a prognostic tool in kidney transplantation: a systematic review

Background

In kidney transplant recipients (KTRs), observational data have reported conflicting findings about the utility of renal resistive index (RRI) in determining outcomes. We aimed to synthesize the current literature and determine the prognostic role of RRI in KTRs.

Methods

We conducted a systematic review to assess the role of RRI in predicting death, graft failure, graft function, and proteinuria. Of the 934 titles/abstracts reviewed, 26 studies were included. There was significant heterogeneity in RRI measurements and thresholds as well as in analytic methods and a meta-analysis could not be performed.

Results

All included studies were observational and included 7049 KTRs. Eight studies analyzed death, of which five reported a significant association with higher RRI. In the remaining three, small sample sizes and lower/multiple RRI thresholds may have limited detection of a statistically significant difference. Three studies investigated all-cause graft failure and an association with RRI was reported but varied by time of RRI measurement. Three out of five studies that analyzed a composite of patient and graft outcomes reported an association with RRI. Evidence analyzing death-censored graft failure, graft failure (unclear if death-censored or all-cause), measures of graft function, and proteinuria were conflicting. Most studies had a moderate to high risk of bias.

Conclusions

RRI likely has a prognostic role in predicting patient outcomes, reflecting patient systemic vascular disease burden rather than graft hemodynamics. Since cardiovascular diseases are a major cause of death and graft loss, RRI may be explored as a non-invasive tool to risk stratify KTRs.

Early graft function and intrarenal resistant index after kidney transplantation using Biolasol-A new solid organ preservation fluid

Biolasol is a newly developed preserving solution for cold organ storage prior to transplantation. To date, only animal model experiments results are available. The aim of this single-center analysis was to summarize the clinical experience concerning the early post-transplant course of kidney grafts preserved with Biolasol in comparison with other preservation solutions. Before transplantation, 173 kidney grafts were preserved using Biolasol and 240 organs with other solutions (University of Wisconsin-UW, Institute Georges Lopez-IGL-1, or StoreProtect Plus solutions). Early graft function was defined based on serum creatinine concentration at day 3 (<3 mg/dL-immediate graft function, IGF or >3 mg/dL-slow graft function, SGF) or the need of dialysis therapy during first post-operative week (delayed graft function, DGF). The analysis included intrarenal resistive indices measured by Doppler sonography early after transplantation and before discharge from the hospital. IGF was more frequent in patients with organs preserved with IGL-1 (33.5%) and StoreProtect Plus (38.8%) than Biolasol (18.5%), whereas there was no difference in the occurrence of DGF. Both initial and discharge median resistance index values were significantly higher in the Biolasol subgroup (0.77 and 0.75) than in all three other subgroups (P values for all comparisons <.001), also after 1:1 propensity score matching for baseline characteristics. Multiple logistic regression analysis based on the propensity score-matched cohort revealed that the use of Biolasol solution [OR 0.59 (0.35-0.98); P < .05] independently decreased the occurrence of IGF. In our single-center clinical experience, kidney preservation using Biolasol solution was associated with significantly higher intrarenal resistant index in comparison with other preservation fluids, as well as worse early graft function than in the IGL-1 and the StoreProtect Plus subgroups. Long-term follow-up is needed in order to assess the kidney graft and patient survival.

The predictive value of resistive index obtained by Doppler ultrasonography early after renal transplantation on long-term allograft function

DUSG is a useful diagnostic tool for the follow-up of renal transplant recipients. The measurement of intrarenal arterial RI by DUSG has been proven to predict short-term AF. The aim of the study was to evaluate the predictive value of DUSG performed during the early after RTx on long-term AF. Seventy patients were enrolled into study. DUSG was performed at third and seventh days after RTx. Patients were divided into two groups according to rate of recovery of graft function as patients with normal graft function and abnormal graft function. Although the RI values were correlated with the AF early after transplantation, they were not correlated with long-term AF. However, the rate of recovery of graft function at early period after RTx was correlated with creatinine level at first year and with glomerular filtration rate at first year and last visit. Although the RI has no predictive value for long-term AF, the rate of recovery of graft function at early post-transplantation period has predictive value for long-term AF; patients with higher RI values early after RTx should be followed carefully for the development of chronic allograft injury.

Impact of ultrasound examination shortly after kidney transplantation

Background

Ultrasound is routinely performed at our transplant unit within the first 48 h of kidney transplantation (KTX). The objective of this study was to evaluate the association of ultrasound results and, in particular, elevated resistance indices (RIs) with the occurrence of surgical complications and allograft outcomes.

Methods

The study included all kidney allograft recipients undergoing transplantation at our center between January 2010 and December 2011 (N = 329). Ultrasound examination was performed on 315 recipients (95.7%).

Results

Delayed graft function was more common in subjects with a high RI (≥0.7) than in patients with an RI < 0.7 (47.2 vs. 28.2%; p = 0.032). A lack of arterial signal was detected in eight patients (2.5%), of whom five had a vascular complication that required surgical therapy. In 12 patients (3.8%), RI was 1 without any other signs of vascular impairment. Even though such values can be a sign of venous thrombosis, no case was observed in any of these patients.

Conclusions

The results of our study suggest that ultrasound evaluation of the transplanted kidney shortly after transplantation is a valuable tool not only for detecting vascular complications but also as a predictor of graft outcome regarding delayed graft function.

Hypothermic machine perfusion improves Doppler ultrasonography resistive indices and long-term allograft function after renal transplantation: a single-centre analysis

OBJECTIVES

To evaluate whether hypothermic machine perfusion (HMP) of transplanted kidneys can improve long-term renal allograft function compared with static cold storage (CS).

METHODS

We evaluated whether graft Doppler ultrasonography resistive indices improved with the use of HMP compared with CS preservation, and examined whether these improvements were predictive of long-term graft function. A total of 30 kidney transplants (15 pairs) were examined. One of the kidney pairs was placed on CS and transplanted first (CS group, n = 15). The other kidney of each pair was placed on HMP and transplanted after the CS group (HMP group, n = 15). Doppler ultrasonography was performed on days 1 and 7 after transplantation and resistive indices were evaluated. The estimated glomerular filtration rate (eGFR) was monitored for 24 months after transplantation.

RESULTS

Despite longer cold ischaemia times, kidneys maintained with HMP had lower resistive indices (P = 0.005) with correspondingly higher eGFR throughout the follow-up. Subgroup analysis showed that the HMP-induced improvement in postoperative eGFR was greatest in kidneys obtained from donation after cardiac death (DCD), even at 2 years after transplantation (P = 0.008).

CONCLUSIONS

HMP of transplant kidneys appears to improve vascular resistance after transplantation and has a positive impact on long-term allograft function compared with CS in the population of recipients of DCD kidneys.

Physiological biomarkers of acute kidney injury: a conceptual approach to improving outcomes

The past 5-10 years have brought significant advances in the identification and validation of novel biochemical biomarkers in the prevention and treatment of acute kidney injury (AKI). These biochemical biomarkers remain research tools but we anticipate that soon they will be employed in clinical practice. A Consensus Conference held by the Acute Dialysis Quality Initiative (ADQI) recently reviewed the evidence, and identified gaps and a research agenda. Furthermore, at this meeting was the birth of an initiative to comprehensively identify new opportunities to characterize the physiological changes during the course of AKI based upon a conceptual framework for the detection and monitoring of renal ischemia-reperfusion injury. This framework includes a transition from monitoring physiological biomarkers of adequate renal perfusion, to pathophysiologic biomarkers of renal hypoperfusion, and finally biomarkers of kidney cell structural injury/damage. Techniques to measure physiological changes in AKI include several physiological variables that might be used in an interactive way to supplement clinical information and biochemical damage biomarkers in the diagnosis and management of AKI. This review summarizes the spectrum of physiological parameters and potential new physiological methods that enable identification of high-risk patients for AKI, facilitate early diagnosis, and differential diagnosis to guide therapeutic management and prognostication. Finally, we propose a research agenda for the next 5 years to facilitate the development and validation of physiological biomarkers in AKI.

Intrarenal resistance index for the assessment of acute renal injury in a rat liver transplantation model

Background

Acute kidney injury (AKI) is a common complication after liver transplantation (LT) and associated with a high mortality. The renal resistive index (RI) is used to assess early renal function impairment in critical care patients. However, limited data are available concerning changes of renal RI and the development of AKI early after reperfusion. We approached to investigate the changes of renal RI and AKI after reperfusion in a rat liver transplantation model.

Methods

Rats were randomly divided into sham group or LT group. Ten rats in each group were used for the hemodynamic study and twenty for Doppler measurements during the procedure. Ten rats were sacrificed 30 min or 2 h after the reperfusion. We harvested kidneys, serum and urine for further analysis of the renal function.

Results

The intrarenal RI increased significantly in the anhepatic stage and decreased significantly after the reperfusion in the LT group compared with sham group (P < 0.05). AKI was seen after the reperfusion in the LT group. No correlation was noted between the RI and renal function parameters 30 min after reperfusion.

Conclusions

The intrarenal RI increased significantly during the anhepatic stage, and decreased significantly early after the reperfusion. Intrarenal RI was unable to assess renal function in a rat liver transplantation model.

Interobserver variability of ultrasound elastography in transplant kidneys: correlations with clinical-Doppler parameters

Real-time sonoelastography (RSE) is a relatively new imaging technique that visualizes relative difference in tissue hardness by evaluating changes in local strain in response to external stress. Our aim was to evaluate the ability of investigators to use sonoelastography to detect differences in renal cortical stiffness and assess the relationship between stiffness and clinical-Doppler parameters. In 42 adult renal transplant recipients, sonoelastography of kidney was performed to calculate the strain ratio (SR) of the central echo complex to the renal parenchyma. Resistive index (RI) and pulsatility index (PI) were also measured. Estimated glomerular filtration rate (eGFR) was calculated. Parenchymal stiffness showed significant positive correlation with RI and PI (r: 0.41 p = 0.007 and r: 0.48 p = 0.001, respectively). Parenchymal stiffness and eGFR did not have a significant correlation (p = 0.42). Interobserver agreement, expressed as intraclass correlation coeffiicient was 0.47 (95% CI: 0.05-0.70). Parenchymal stiffness (SR) showed significant positive correlation with RI and PI but sonoelastography has also wide range intra- and low interobserver agreement in renal transplants. Further studies are warranted in larger patient groups to determine the reliability of sonoelastography in renal transplants.

Color Doppler indexes in early phase after kidney transplantation and their association with kidney function on six month follow up

BACKGROUND

Doppler ultrasonography (DU) and measurement of its indexes, resistive index (RI) and pulsatility index (PI), is used to investigate transplanted kidney hemodynamic status and function. The aim of this study was to determine the correlation between Doppler indexes in the early phase after transplantation with long-term transplanted kidney function.

MATERIALS AND METHODS

In this cross-sectional study on 38 newly kidney transplant patients, we performed DU with assessment of its indexes within 48 hours, 1 week, and 6 months after kidney transplantation. Serum creatinine after stability and 6 months after kidney transplantation were assessed. Cyclosporine level was measured 1 week after kidney transplantation and compared with DU indexes.

RESULTS

About 71% of kidney transplanted patients reached their normal initial creatinine level(cr<1.5 mg/ dl) and 28% of all patients were involved in kidney dysfunction after 6 months (increase in basic creatinine level more than 25%).There was no significant difference between mean RI and PI in patients with normal and disturbed kidney function based on creatinine level in early posttransplantation period but there was linear correlation between mean RI and PI within 48 hours and 1 week with kidney function after 6 months. Also no association between cyclosporine level and RI and PI was shown. There was a direct association between age and the levels of RI and PI 6 months after transplantation.

CONCLUSION

This study suggests assessment of RI and PI in early period after transplantation and can be used as predictive parameters for long-term function of transplanted kidney and RI more than 0.80 in early phase after transplantation has an acceptable sensitivity and specificity to predict long-term kidney dysfunction.

Prognostic impact of renal arterial resistance index upon renal allograft survival: the time point matters

BACKGROUND

The renal arterial resistance index (RI) is reported to be a significant predictive parameter for renal allograft failure or death. The influence of the time point after renal transplantation on its predictive power has not been sufficiently evaluated. We performed a retrospective analysis of RI and its power to predict renal allograft failure or death with special emphasis on the time point of RI measurement.

METHODS

The present analysis is based on ultrasonographically recorded intrarenal arterial RI measurements, routinely obtained in our outpatient department, over a period of 13 years. Altogether, 88 patients with an RI measurement 0-3, 3-6 and 12-18 months after transplantation were included and retrospectively stratified into two groups according to the RI: those with an index >0.75 and those with an index of ≤0.75.

RESULTS

Twenty patients (23%) reached the combined end point, i.e. allograft failure with a return to dialysis or death. The RI measured early after transplantation (0-3 and 3-6 months) did not predict the end point, whereas the RI obtained between 12 and 18 months showed a significant predictive value for renal transplant failure or death in a univariate approach [Wald test, P = 0.0013, hazard ratio (HR) 4.787, 95% confidence interval (CI) 1.846-12.411]. At 12-18 months after transplantation, 14% (12 patients) of the study population had an RI >0.75. Seven (58%) of these patients reached the end point versus 13 of 76 patients (17%) with an RI ≤0.75. In a multivariate Cox model, the RI measured between 12 and 18 months after transplantation exhibited the highest hazard ratio (HR 6.191, 95% CI 2.288-16.756, P = 0.0003) for transplant failure or death.

CONCLUSION

In our hands, the RI obtained during the first 6 months after transplantation failed to predict renal allograft failure or death, whereas the RI measured 12-18 months after transplantation appeared useful to predict long-term allograft outcomes.

An association between the methylenetetrahydrofolate reductase (MTHFR) C677T mutation and inflammation markers related to cardiovascular disease

BACKGROUND

Prospective studies have identified many markers of systemic inflammation that are powerful predictors of future cardiovascular events. The methylenetetrahydrofolate reductase (MTHFR) C677T genotype, a common polymorphism that induces hyperhomocysteinaemia, has been proposed as a genetic risk factor for cardiovascular disease. In this work, we evaluated the relationship between the levels of inflammation markers and MTHFR genotype among cardiovascular disease free subjects of the ATTICA study.

METHODS

During 2001-2002, we randomly enrolled for genetic evaluation 574 subjects from Attica region, Greece. In this work, we investigated demographic, lifestyle, clinical, biochemical and genetic information from 322 men (46+/-13 years) and 252 women (45+/-14 years). Among other characteristics, we measured various inflammatory markers levels in relation to C677T MTHFR genotype distribution.

RESULTS

The MTHFR genotypes distribution was: homozygous normal (CC) genotype, 41%; heterozygous (CT), 48%; and homozygous mutant (TT) genotype, 11%. C-reactive protein (CRA), fibrinogen, white blood cell (WBC) counts and amyloid-a levels were higher in TT compared to CC and CT genotypes (p<0.01), in both genders, even after controlling for various potential confounders.

CONCLUSION

The observed association between markers of systemic inflammation with MTHFR genotype may state a hypothesis for a common pathobiological mechanism between inflammation process and MTHFR, which is a key enzyme in homocysteine (Hcy) metabolism.