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.

Artery Wall Assessment Helps Predict Kidney Transplant Outcome

Background

Kidney transplant recipients have high cardiovascular risk, and vascular inflammation may play an important role. We explored whether the inflammatory state in the vessel wall was related to carotid intima-media thickness (c-IMT) and patient survival following kidney transplantation.

Methods

In this prospective observational cohort study we measured c-IMT and expression of proinflammatory cytokines and adhesion molecules in the inferior epigastric artery in 115 kidney transplant candidates. Another c-IMT measurement was done 1-year post-transplantation in 107. By stepwise multiple regression analysis we explored factors associated with baseline c-IMT and their changes over time. Multivariate Cox regression analysis was constructed to identify risk factors for mortality.

Results

A worse cardiovascular profile (older age, smoker, diabetic, carotid plaque, systolic blood pressure and vascular calcification) and higher VCAM-1 levels were found in patients in the highest baseline c-IMT tertile, who also had a worse survival. Factors independently related to baseline c-IMT were age (β=0.369, P<0.0001), fasting glucose (β=0.168, P=0.045), smoking (β=0.228, P=0.003) and VCAM-1 levels (β=0.244, P=0.002). Independent factors associated with c-IMT measurement 1-year post-transplantation were baseline c-IMT (β=-0.677, P<0.0001), post-transplant diabetes (β=0.225, P=0.003) and triglycerides (β=0.302, P=0.023). Vascular VCAM-1 levels were associated with increased risk of mortality in bivariate and multivariate Cox regression. Notably, nearly 50% of patients showed an increase or maintenance of high c-IMT 1 year post-transplantation and these patients experienced a higher mortality (13 versus 3.5%; P=0.021).

Conclusion

A worse cardiovascular profile and a higher vascular VCAM-1 protein levels at time of KT are related to subclinical atheromatosis. This could lead to a higher post-transplant mortality. Pre-transplant c IMT, post-transplant diabetes and triglycerides at 1-year post-transplantation may condition a high c-IMT measurement post-transplantation, which may decrease patient survival.

Impact of late calcineurin inhibitor withdrawal on ambulatory blood pressure and carotid intima media thickness in renal transplant recipients

BACKGROUND

Calcineurin inhibitors (CNIs) have an unfavorable cardiovascular risk profile in renal transplant recipients. The aim of this substudy was to assess the effects of late CNI or mycophenolate mofetil (MMF) withdrawal on ambulatory blood pressure monitoring and carotid intima media thickness.

METHODS

A total of 119 stable renal transplant recipients on triple regimen with steroids, a CNI and MMF were randomized into either the concentration-controlled CNI or MMF withdrawal groups. Patients were treated for traditional cardiovascular risk factors according to predefined targets. Ambulatory blood pressure monitoring and measurements of intima media thickness were performed at baseline and after 1, 2, and 3 years after randomization.

RESULTS

CNI withdrawal resulted in a significant decline in both ambulatory day- and nighttime blood pressures (daytime: systolic blood pressure, -1.6 mm Hg/y, P=0.018; diastolic blood pressure, -1.3 mm Hg/y, P=0.002; nighttime systolic blood pressure: -1.9 mm Hg/y, P=0.008; diastolic blood pressure: -1.3 mm Hg/y, P=0.014), which was not observed after MMF withdrawal. There was no difference in the proportion of nocturnal nondippers (both groups, 69%, P=0.95). Despite the reduction in ambulatory blood pressure, no effect of CNI withdrawal on carotid intima media thickness was found.

CONCLUSION

In stable renal transplant recipients, late CNI withdrawal from a triple drug regimen decreased blood pressure in comparison with MMF withdrawal but had no specific impact on carotid intima media thickness. Considering the high prevalence of hypertension in patients on CNI therapy, most stable renal transplant recipients may benefit from late CNI withdrawal by improved blood pressure control.

Correlation of histopathologic and dynamic tissue perfusion measurement findings in transplanted kidneys

Background

Cortical perfusion of the renal transplant can be non-invasively assessed by color Doppler ultrasonography. We performed the Dynamic Tissue Perfusion Measurement (DTPM) of the transplant’s renal cortex using color Doppler ultrasonography (PixelFlux technique), and compared the results with the histopathological findings of transplant biopsies.

Methods

Ninety-six DTPM studies of the renal transplant’s cortex followed by transplant biopsies were performed in 78 patients. The cortical perfusion data were compared with the parameter of peritubular inflammatory cell accumulation (PTC 0 to 3) based on Banff-classification system.

Results

A significant decrease of cortical perfusion could be demonstrated as the inflammatory cells accumulation in peritubular capillaries increased. Increasing peritubulitis caused a perfusion loss from central to distal layers of 79% in PTC 0, of 85% in PTC 1, of 94% in PTC 2, and of 94% in PTC 3. Furthermore, the perfusion loss due to peritubular inflammation was more prominent in the distal cortical layer. The extent of perfusion decline with increasing peritubulitis (from PTC 0 to PTC 3) was 64% in proximal 20% cortical layer (p20), 63% in proximal 50% cortical layer (p50), increased to 76% in distal 50% cortical layer (d50), and peaked at 90% in the distal 20% cortical layer (d20). For those without peritubulitis (PTC 0), the increase in the the Interstitial Fibrosis/Tubular Atrophy (IF/TA) score was accompanied by a significantly increased cortical perfusion. A Polyomavirus infection was associated with an increased cortical perfusion.

Conclusions

Our study demonstrated that the perfusion of the renal transplant is associated with certain pathological changes within the graft. DTPM showed a significant reduction of cortical perfusion in the transplant renal cortex related to peritubular capillary inflammation.

The renal arterial resistive index and stage of chronic kidney disease in patients with renal allograft

Objective

The study investigated the optimal threshold value of renal arterial resistive index as assessed by Doppler ultrasonography determining chronic kidney disease stage 4 or higher in patients with renal allograft.

Methods

In a cross-sectional study the renal arterial resistive index were obtained in interlobar arteries by Doppler ultrasonography in 78 patients with renal allograft. The stage of chronic kidney disease was determined by the estimated glomerular filtration rate equation.

Results

The median renal arterial resistive index was 0.61 (interquartile range, 0.56 to 0.66). We observed a significant association between renal arterial resistive index above the upper quartile and chronic kidney disease stage 4 or higher (relative risk, 4.64; 95% confidence interval, 1.71 to 12.55; p = 0.003 by Fisher’s exact test). Multivariate logistic regression analysis showed that renal arterial resistive indices (p = 0.02) and time since transplantation (p = 0.04), but not age, gender, or blood pressure were significantly associated with chronic kidney disease stage 4 or higher.

Conclusion

A renal arterial resistive index higher than 0.66 may determine the threshold value of chronic kidney disease stage 4 or higher in patients with renal allograft.

Early kidney graft size and Doppler parameters are associated with kidney graft function 1 year after transplantation

BACKGROUND

The aim of this study was to assess the association of various ultrasonography (US) and Doppler parameters of kidney graft as measured at 1 month posttransplant with 1-year graft function.

MATERIALS AND METHODS

The study cohort included 125 adult recipients of deceased donor kidney transplantations between January 2006 and February 2009. All patients underwent an US-Doppler examination performed by a trained nephrologist at 1 month posttransplant using an Acuson-Siemens Sequoia 512. Graft length and intrarenal Doppler indices were measured at the midsegmental artery level. Relative graft size was calculated by dividing graft length with body mass index. Graft function was assessed at 1 year by estimated glomerular filtration rate (eGFR) using the 4-variable Modification of Diet in Real Disease study equation. Linear and logistic regression analyses were used to assess the relationship between US-Doppler parameters and eGFR.

RESULTS

Univariate linear regression showed a significant correlation between eGFR at 1 year and graft length at 1 month (P = .009), relative graft length <0.50 cm per kg/m(2) (P = .004), resistance index >0.75 (P = .031), and end-diastolic velocity <9 cm/sec (P = .006). Logistic regression analyses showed that eGFR <60 mL/min/1.73 m(2) at 1 year was significantly associated with graft length <12 cm at 1 month (odds ratio [OR], 2.4; 95% confidence interval [CI], 1.16-4.92; P = .017), relative graft length <0.5 cm per kg/m(2) (OR, 2.54; 95% CI, 1.20-5.35; P = .014), resistance index >0.75 (OR, 2.86; 95% CI, 1.30-6.29; P = .009), and end-diastolic velocity <9 cm/sec (OR, 2.37; 95% CI, 1.01-5.56; P = .047).

CONCLUSION

In this retrospective analysis, kidney transplant recipients with greater graft length at 1 month, specifically when standardized to body size, showed better graft function at 1 year posttransplantation. Higher intrarenal diastolic blood flow and lower resistance index at 1 month were also predictive of better graft function at 1 year.