Circulating thrombospondin-2 level for identifying individuals with rapidly declining kidney function trajectory in type 2 diabetes: a prospective study of the Hong Kong West Diabetes Registry.

BACKGROUND: Thrombospondin-2 (TSP2) is a matricellular protein with tissue expression induced by hyperglycaemia. TSP2 has been implicated in non-diabetic renal injury in preclinical studies and high circulating levels were associated with worse kidney function in cross-sectional clinical studies. Therefore, we investigated the prospective associations of circulating TSP2 level with kidney function decline and the trajectories of estimated glomerular filtration rate (eGFR) in type 2 diabetes. METHODS: Baseline serum TSP2 level was measured in 5471 patients with type 2 diabetes to evaluate its association with incident eGFR decline, defined as ≥ 40% sustained eGFR decline, using multivariable Cox regression analysis. Among participants with relatively preserved kidney function (Baseline eGFR ≥ 60 ml/min/1.73m2), joint latent class modelling was employed to identify three different eGFR trajectories. Their associations with baseline serum TSP2 was evaluated using multinomial logistic regression analysis. The predictive performance of serum TSP2 level was examined using time-dependent c-statistics and calibration statistics. RESULTS: Over a median follow-up of 8.8 years, 1083 patients (19.8%) developed eGFR decline. Baseline serum TSP2 level was independently associated with incident eGFR decline (HR 1.21, 95%CI 1.07-1.37, P = 0.002). With internal validation, incorporating serum TSP2 to a model of clinical risk factors including albuminuria led to significant improvement in c-statistics from 83.9 to 84.4 (P < 0.001). Among patients with eGFR ≥ 60 ml/min/1.73m2, baseline serum TSP2 level was independently associated with a rapidly declining eGFR trajectory (HR 1.63, 95%CI 1.26-2.10, P < 0.001). CONCLUSION: Serum TSP2 level was independently associated with incident eGFR decline, particularly a rapidly declining trajectory, in type 2 diabetes.

Multi-phasic eGFR trajectory during follow up and long-term graft failure after kidney transplantation.

BACKGROUND: The prevailing assumption is that following kidney transplantation the pattern of kidney function decline is consistent. Nevertheless, numerous factors leading to graft loss may emerge, altering the trajectory of kidney function. In this study, we aim to assess alterations in estimated glomerular filtration rate (eGFR) trajectory over an extended period of follow-up and examine its correlation with graft survival. METHODS: We calculated eGFR using all creatinine values available from 1-year post transplantation to the end of follow-up. For pattern analysis, we used a piecewise linear model. RESULTS: Nine hundred eighty-eight patients were included in the study. After a median follow-up of 5.2 years, 297 (30.1%) patients had a multi-phasic eGFR trajectory. Change in eGFR trajectory was associated with increased risk for graft failure (HR 7.15, 95% CI 5.17-9.89, p < .001), longer follow-up time, younger age, longer cold ischemia time, high prevalence of acute rejection, longer hospitalization and a lower initial eGFR. Of the 988 patients included in the study, 494 (50.0%) had a mono-phasic stable trajectory, 197 (19.9%) had a mono-phasic decreasing trajectory, 184 (18.6%) had bi-phasic decreasing trajectory (initial stability and then decline, 46(4.7%) had a bi-phasic stabilized (initial decline and then stabilization) and 67(6.8%) had a more complex trajectory (tri-phasic). Out of the total 144 patients who experienced graft loss, the predominant pattern was a bi-phasic decline characterized by a bi-linear trajectory (66 events, 45.8%). CONCLUSIONS: Changes in eGFR trajectory during long-term follow-up can serve as a valuable tool for assessing the underlying mechanisms contributing to graft loss.

CKD Progression From the Time of Estimated GFR-Based Waitlist Eligibility and Racial Disparities in Transplant Access.

RATIONALE & OBJECTIVE: Equations for estimated glomerular filtration rate (eGFR) that incorporate a term for race assign a higher value to Black individuals compared to non-Black individuals for the same sex, age, and serum creatinine concentration. This difference may contribute to racial disparities in kidney transplant access. We sought to (1) compare time from meeting a transplant eligibility threshold of eGFR ≤20 mL/min/1.73 m2 to kidney failure with replacement therapy (KFRT) among Black, Hispanic, and White patients, and (2) assess the impact of incorporation of race into eGFR expressions on establishment of waitlist eligibility and time from eligibility to KFRT. STUDY DESIGN: Retrospective cohort. SETTING & PARTICIPANTS: Using the OptumLabs Data Warehouse, we assembled a cohort of 40,042 White, 8,519 Black, and 3,569 Hispanic patients having at least one eGFR value between 20 and 60 mL/min/1.73 m2 within the preceding 2 years and an incident outpatient eGFR of ≤20 mL/min/1.73 m2 between 2008-2018, using the CKD-EPI creatinine equation that includes a term for race coded as Black or non-Black. We then reassembled a Black patient cohort based on incident eGFR ≤20 mL/min/1.73 m2 (n = 11,269) estimated using the same CKD-EPI equation but coding Black patients as non-Black. EXPOSURE: Race/ethnicity. OUTCOME: Time to KFRT. ANALYTICAL APPROACH: Unadjusted and adjusted Fine-Gray models; linear regression to compute eGFR slopes. RESULTS: By 3 years, the cumulative incidence of KFRT was 20.5% among White patients, 40.9% among Hispanic patients, 36% among Black patients whose GFR was estimated using a race term coded as Black, and 28.7% among Black patients whose GFR was estimated using a race term coded as non-Black. In fully adjusted analyses including 11,269 Black patients with an eGFR ≤20 mL/min/1.73 m2 based on coding them as non-Black, KFRT risk remained greater among Black (HR, 1.28 [95% CI, 1.15-1.43]) and Hispanic (HR, 1.66 [95% CI, 1.18-2.31]) patients than among White patients. Based on slopes of eGFR decline, coding Black patients as non-Black would allow earlier waitlist activation by an estimated median of 0.5 [interquartile range, 0.27-1.23] years. LIMITATIONS: Inability to exclude individuals who would not be kidney transplant candidates if comprehensively evaluated. CONCLUSIONS: A uniform eGFR threshold provides less opportunity for being placed on the transplant waitlist among Black and Hispanic patients. For many Black patients, estimation of GFR as if their race category were non-Black would allow substantially earlier waitlisting but would not eliminate their shorter time to KFRT and reduced opportunity for preemptive transplantation compared with White patients.

Estimated GFR Slope Across CKD Stages in Primary Hyperoxaluria Type 1.

RATIONALE & OBJECTIVE: Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disorder of glyoxylate metabolism that results in early-onset kidney stone disease, nephrocalcinosis, and kidney failure. There is an unmet need for reliable markers of disease progression to test effectiveness of new treatments for patients with PH. In this study, we assessed the rate of estimated glomerular filtration rate (eGFR) decline across chronic kidney disease (CKD) glomerular filtration rate (GFR) categories (CKD G2-G5) in a cohort of patients with PH1. STUDY DESIGN: Retrospective observational study. SETTING & PARTICIPANTS: Patients with PH1 enrolled in the Rare Kidney Stone Consortium (RKSC) registry who did not have kidney failure at diagnosis and who had at least 2 eGFR values recorded from within 1 month of diagnosis until their last contact date or incident kidney failure event. PREDICTORS: CKD GFR category, baseline patient and laboratory characteristics. OUTCOME: Annualized rate of eGFR decline. ANALYTICAL APPROACH: Generalized estimating equations and linear regression were used to evaluate the associations between CKD GFR category, baseline patient and laboratory characteristics, and annual change in eGFR during follow-up. RESULTS: Compared with the slope in CKD G2 (-2.3 mL/min/1.73 m2 per year), the mean annual eGFR decline was nominally steeper in CKD G3a (-5.3 mL/min/1.73 m2 per year) and statistically significantly more rapid in CKD G3b and G4 (-14.7 and -16.6 mL/min/1.73 m2 per year, respectively). In CKD G2, older age was associated with a more rapid rate of eGFR decline (P = 0.01). A common PH1-causing variant of alanine glyoxylate aminotransferase, a glycine to arginine substitution at amino acid 170 (G170R), appeared to be associated with less severe annual decline in eGFR. LIMITATIONS: Data at regular time points were not available for all patients due to reliance on voluntary reporting in a retrospective rare disease registry. CONCLUSIONS: The eGFR decline was not uniform across CKD GFR categories in this PH1 population, with a higher rate of eGFR decline in CKD G3b and G4. Thus, CKD GFR category needs to be accounted for when analyzing eGFR change in the setting of PH1.

Biomarkers During Recovery From AKI and Prediction of Long-term Reductions in Estimated GFR.

RATIONALE & OBJECTIVE: The effects of acute kidney injury (AKI) on long-term kidney function, cardiovascular disease, and mortality are well documented. We aimed to identify biomarkers for the estimation of risk of new or worsening chronic kidney disease (CKD) following AKI. STUDY DESIGN: Prospective cohort study. SETTING & PARTICIPANTS: Adults from a single clinical center who experienced AKI between May 2013 and May 2016 and survived until 3 years after the hospitalization during which AKI occurred. Participants included those with and without preexisting CKD. PREDICTORS: Panel of 11 plasma biomarkers measured 3 months after hospitalization. OUTCOME: Kidney disease progression, defined as a≥25% decrease in estimated glomerular filtration rate (eGFR) combined with worsening CKD stage, assessed 3 years after the occurrence of AKI. ANALYTICAL APPROACH: Associations between biomarkers and kidney disease progression were evaluated in multivariable logistic regression models. Importance of predictor variables was assessed by constructing multiple decision trees, with penalized least absolute shrinkage and selection operator logistic regression for variable selection used to produce multivariable models. RESULTS: A total of 500 patients were studied. Soluble tumor necrosis factor receptor (sTNFR) 1, sTNFR2, cystatin C, neutrophil gelatinase-associated lipocalin, 3-month eGFR, and urinary albumin-creatinine ratio were independently associated with kidney disease progression and were more important than AKI severity or duration. A multivariable model containing sTNFR1, sTNFR2, cystatin C, and eGFR discriminated between those with and without kidney disease progression (area under the curve, 0.79 [95% CI, 0.70-0.83]). Optimizing the cutoff point to maximize utility as a "rule-out" test to identify those at low risk increased the sensitivity of the model to 95% and its negative predictive value to 92%. LIMITATIONS: Lack of external validation cohort. Analyses limited to patients who survived for 3 years after AKI. Mixed population of patients with and without baseline CKD. CONCLUSIONS: A panel of plasma biomarkers measured 3 months after discharge from a hospitalization complicated by AKI provides a potential opportunity to identify patients who are at very low risk of incident or worsening CKD. Further study is required to determine its clinical utility through independent prospective validation.

Time-Updated Changes in Estimated GFR and Proteinuria and Major Adverse Cardiac Events: Findings from the Chronic Renal Insufficiency Cohort (CRIC) Study.

RATIONALE & OBJECTIVE: Evaluating repeated measures of estimated glomerular filtration rate (eGFR) and urinary protein-creatinine ratio (UPCR) over time may enhance our ability to understand the association between changes in kidney parameters and cardiovascular disease risk. STUDY DESIGN: Prospective cohort study. SETTING & PARTICIPANTS: Annual visit data from 2,438 participants in the Chronic Renal Insufficiency Cohort (CRIC). EXPOSURES: Average and slope of eGFR and UPCR in time-updated, 1-year exposure windows. OUTCOMES: Incident heart failure, atherosclerotic cardiovascular disease events, death, and a composite of incident heart failure, atherosclerotic cardiovascular disease events, and death. ANALYTICAL APPROACH: A landmark analysis, a dynamic approach to survival modeling that leverages longitudinal, iterative profiles of laboratory and clinical information to assess the time-updated 3-year risk of adverse cardiovascular outcomes. RESULTS: Adjusting for baseline and time-updated covariates, every standard deviation lower mean eGFR (19mL/min/1.73m2) and declining slope of eGFR (8mL/min/1.73m2 per year) were independently associated with higher risks of heart failure (hazard ratios [HRs] of 1.82 [95% CI, 1.39-2.44] and 1.28 [95% CI, 1.12-1.45], respectively) and the composite outcome (HRs of 1.32 [95% CI, 1.11-1.54] and 1.11 [95% CI, 1.03-1.20], respectively). Every standard deviation higher mean UPCR (136mg/g) and increasing UPCR (240mg/g per year) were also independently associated with higher risks of heart failure (HRs of 1.58 [95% CI, 1.28-1.97] and 1.20 [95% CI, 1.10-1.29], respectively) and the composite outcome (HRs of 1.33 [95% CI, 1.17-1.50] and 1.12 [95% CI, 1.06-1.18], respectively). LIMITATIONS: Limited generalizability of annual eGFR and UPCR assessments; several biomarkers for cardiovascular disease risk were not available annually. CONCLUSIONS: Using the landmark approach to account for time-updated patterns of kidney function, average and slope of eGFR and proteinuria were independently associated with 3-year cardiovascular risk. Short-term changes in kidney function provide information about cardiovascular risk incremental to level of kidney function, representing possible opportunities for more effective management of patients with chronic kidney disease.

Changes in GFR and Albuminuria in Routine Clinical Practice and the Risk of Kidney Disease Progression.

RATIONALE & OBJECTIVE: Changes in urinary albumin-creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR) have been used separately as alternative kidney disease outcomes in randomized trials. We tested the hypothesis that combined changes in UACR and eGFR predict advanced kidney disease better than either alone. STUDY DESIGN: Observational cohort study. SETTING & PARTICIPANTS: 91,319 primary care patients assembled from the Clinical Practice Research Datalink in the United Kingdom between 2000 and 2015. EXPOSURES: Changes in UACR and eGFR (categorized as ≥30% increase, stable, or ≥30% decrease), alone and in combination, over a 3-year period. OUTCOMES: The primary outcome was advanced CKD (sustained eGFR <30 mL/min/1.73 m2); secondary outcomes included kidney failure, cardiovascular disease, and all-cause mortality. ANALYTICAL APPROACH: Multivariable Cox regression with bias from missing values assessed using multiple imputation; discrimination statistics compared across exposure groups. RESULTS: 91,319 individuals were studied, with a mean eGFR of 72.6 mL/min/1.73 m2 and median UACR of 9.7 mg/g; 70,957 (77.7%) had diabetes. During a median follow-up of 2.9 years, 2,541 people progressed to advanced CKD. Compared with stable values, hazard ratios for a ≥30% increase in UACR and ≥30% decrease in eGFR were 1.78 (95% CI, 1.59-1.98) and 7.53 (95% CI, 6.70-8.45), respectively, for the outcome of advanced CKD. Compared with stable values of both, the hazard ratio for the combination of an increase in UACR and a decrease in eGFR was 15.15 (95% CI, 12.43-18.46) for the outcome of advanced CKD. The combination of changes in UACR and eGFR predicted kidney outcomes better than either alone. LIMITATIONS: Selection bias, relatively small proportion of individuals without diabetes, and very few kidney failure events. CONCLUSIONS: In a large-scale general population, the combination of an increase in UACR and a decrease in eGFR was strongly associated with the risk of advanced CKD. Further assessment of combined changes in UACR and eGFR as an alternative outcome for kidney failure in trials of CKD progression is warranted.

Biomarkers of Kidney Tubule Health, CKD Progression, and Acute Kidney Injury in SPRINT (Systolic Blood Pressure Intervention Trial) Participants.

RATIONALE & OBJECTIVE: The Systolic Blood Pressure Intervention Trial (SPRINT) compared the effect of intensive versus standard systolic blood pressure targets on cardiovascular morbidity and mortality. In this ancillary study, we evaluated the use of exploratory factor analysis (EFA) to combine biomarkers of kidney tubule health in urine and plasma and then study their role in longitudinal estimated glomerular filtration rate (eGFR) change and risk of acute kidney injury (AKI). STUDY DESIGN: Observational cohort nested in a clinical trial. SETTING & PARTICIPANTS: 2,351 SPRINT participants with eGFR < 60 mL/min/1.73 m2 at baseline. EXPOSURE: Levels of neutrophil gelatinase-associated lipocalin (NGAL), interleukin 18 (IL-18), chitinase-3-like protein (YKL-40), kidney injury molecule 1 (KIM-1), monocyte chemoattractant protein 1 (MCP-1), α1-microglobulin (A1M) and ß2-microglobulin (B2M), uromodulin (UMOD), fibroblast growth factor 23 (FGF-23), and intact parathyroid hormone (PTH). OUTCOME: Longitudinal changes in eGFR and risk of AKI. ANALYTICAL APPROACH: We performed EFA to capture different tubule pathophysiologic processes. We used linear mixed effects models to evaluate the association of each factor with longitudinal changes in eGFR. We evaluated the association of the tubular factors scores with AKI using Cox proportional hazards regression. RESULTS: From 10 biomarkers, EFA generated 4 factors reflecting tubule injury/repair (NGAL, IL-18, and YKL-40), tubule injury/fibrosis (KIM-1 and MCP-1), tubule reabsorption (A1M and B2M), and tubule reserve/mineral metabolism (UMOD, FGF-23, and PTH). Each 1-SD higher tubule reserve/mineral metabolism factor score was associated with a 0.58% (95% CI, 0.39%-0.67%) faster eGFR decline independent of baseline eGFR and albuminuria. Both the tubule injury/repair and tubule injury/fibrosis factors were independently associated with future risk of AKI (per 1 SD higher, HRs of 1.18 [95% CI, 1.10-1.37] and 1.23 [95% CI, 1.02-1.48], respectively). LIMITATIONS: The factors require validation in other settings. CONCLUSIONS: EFA allows parsimonious subgrouping of biomarkers into factors that are differentially associated with progressive eGFR decline and AKI. These subgroups may provide insights into the pathological processes driving adverse kidney outcomes.

Kidney Histopathology and Prediction of Kidney Failure: A Retrospective Cohort Study.

RATIONALE & OBJECTIVE: The use of kidney histopathology for predicting kidney failure is not established. We hypothesized that the use of histopathologic features of kidney biopsy specimens would improve prediction of clinical outcomes made using demographic and clinical variables alone. STUDY DESIGN: Retrospective cohort study and development of a clinical prediction model. SETTING & PARTICIPANTS: All 2,720 individuals from the Biopsy Biobank Cohort of Indiana who underwent kidney biopsy between 2002 and 2015 and had at least 2 years of follow-up. NEW PREDICTORS & ESTABLISHED PREDICTORS: Demographic variables, comorbid conditions, baseline clinical characteristics, and histopathologic features. OUTCOMES: Time to kidney failure, defined as sustained estimated glomerular filtration rate ≤ 10mL/min/1.73m2. ANALYTICAL APPROACH: Multivariable Cox regression model with internal validation by bootstrapping. Models including clinical and demographic variables were fit with the addition of histopathologic features. To assess the impact of adding a histopathology variable, the amount of variance explained (r2) and the C index were calculated. The impact on prediction was assessed by calculating the net reclassification index for each histopathologic variable and for all combined. RESULTS: Median follow-up was 3.1 years. Within 5 years of biopsy, 411 (15.1%) patients developed kidney failure. Multivariable analyses including demographic and clinical variables revealed that severe glomerular obsolescence (adjusted HR, 2.03; 95% CI, 1.51-2.03), severe interstitial fibrosis and tubular atrophy (adjusted HR, 1.99; 95% CI, 1.52-2.59), and severe arteriolar hyalinosis (adjusted HR, 1.53; 95% CI, 1.14-2.05) were independently associated with the primary outcome. The addition of all histopathologic variables to the clinical model yielded a net reclassification index for kidney failure of 5.1% (P < 0.001) with a full model C statistic of 0.915. Analyses addressing the competing risk for death, optimism, or shrinkage did not significantly change the results. LIMITATIONS: Selection bias from the use of clinically indicated biopsies and exclusion of patients with less than 2 years of follow-up, as well as reliance on surrogate indicators of kidney failure onset. CONCLUSIONS: A model incorporating histopathologic features from kidney biopsy specimens improved prediction of kidney failure and may be valuable clinically. Future studies will be needed to understand whether even more detailed characterization of kidney tissue may further improve prognostication about the future trajectory of estimated glomerular filtration rate.

Timing of Recovery From Moderate to Severe AKI and the Risk for Future Loss of Kidney Function.

RATIONALE & OBJECTIVE: The extent of recovery of kidney function following acute kidney injury (AKI) is known to be associated with future chronic kidney disease. Less is known about how the timing of recovery affects the rate of future loss of kidney function. STUDY DESIGN: We performed a retrospective cohort study examining the independent association between the timing of recovery from moderate to severe AKI and future loss of kidney function. SETTING & PARTICIPANTS: 47,903 adult US veterans with stage 2 or 3 AKI who recovered to within 120% of baseline creatinine level within 90 days of peak injury. EXPOSURE: The timing of recovery of kidney function from peak inpatient serum creatinine level grouped into 1 to 4, 5 to 10, 11 to 30, and 31 to 90 days. OUTCOME: A sustained 40% decline in estimated glomerular filtration rate below that calculated from the last serum creatinine level available during the 90-day recovery period or kidney failure (2 outpatient estimated glomerular filtration rates<15mL/min/1.73m2, dialysis procedures > 90 days apart, kidney transplantation, or registry within the US Renal Data System). ANALYTICAL APPROACH: Time to the primary outcome was examined using multivariable Cox proportional hazards regression. RESULTS: Among 47,903 patients, 29,316 (61%), 10,360 (22%), 4,520 (9%), and 3,707 (8%) recovered within 1 to 4, 5 to 10, 11 to 30, and 31 to 90 days, respectively. With a median follow-up of 42 months, unadjusted incidence rates for the kidney outcome were 2.01, 3.55, 3.86, and 3.68 events/100 person-years, respectively. Compared with 1 to 4 days, recovery within 5 to 10, 11 to 30, and 31 to 90 days was associated with increased rates of the primary outcome: adjusted HRs were 1.33 (95% CI, 1.24-1.43), 1.41 (95% CI, 1.28-1.54), and 1.58 (95% CI, 1.43-1.75), respectively. LIMITATIONS: Predominately male population, residual confounding, and inability to make causal inferences because of the retrospective observational study design. CONCLUSIONS: The timing of recovery provides an added dimension to AKI phenotyping and prognostic information regarding the future occurrence of loss of kidney function. Studies to identify effective interventions on the timing of recovery from AKI are warranted.

Trends in Kidney Function Outcomes Following RAAS Inhibition in Patients With Heart Failure With Reduced Ejection Fraction.

RATIONALE & OBJECTIVE: Angiotensin-converting enzyme (ACE) inhibitors are beneficial in heart failure with reduced ejection fraction (HFrEF). We sought to describe longitudinal trends in estimated glomerular filtration rate (eGFR) in HFrEF and how ACE-inhibitor therapy influences these changes. STUDY DESIGN: Post hoc analysis of trial data. SETTINGS & PARTICIPANTS: Symptomatic (Treatment Trial, n=2,423) and asymptomatic (Prevention Trial, n=4,094) patients from the Studies of Left Ventricular Dysfunction (SOLVD). EXPOSURE: Enalapril versus placebo. OUTCOMES: Early and long-term eGFR slope (ie, within and after the first 6 weeks) and 4 kidney end points: (1) serum creatinine level increase by≥0.3mg/dL, (2)>30% eGFR decline, (3)>40% eGFR decline, and (4) incident eGFR<30mL/min/1.73m2. ANALYTICAL APPROACH: Shared parameter models, multivariable Cox regression models. RESULTS: Baseline mean eGFR was lower in the Treatment Trial than in the Prevention Trial, 69.5±19.8 (SD) versus 76.2±18.6mL/min/1.73m2. Following randomization, an early eGFR decline occurred in the enalapril group; however, slopes during the median 3-year follow-up were not statistically different by randomization arm in either the Treatment Trial (-0.84 in enalapril vs-1.36mL/min/1.73m2 per year in placebo; P=0.08) or Prevention Trial (-1.27 in enalapril vs-1.36mL/min/1.73m2 per year in placebo; P=0.7). Random assignment to enalapril treatment increased the risk for all 4 outcomes in the Treatment Trial in the first 6-week period (HRs were 1.48 [95% CI, 1.10-1.99] for creatinine increase by≥0.3mg/dL; 1.38 [95% CI, 0.98-1.94] for eGFR decline> 30%; 2.60 [95% CI, 1.30-5.21] for eGFR decline> 40%; and 4.71 [95% CI, 1.78-12.50] for eGFR<30mL/min/1.73m2), but after the first year was not significantly associated with increased risk. A similar albeit less pronounced pattern was observed in the Prevention Trial, with risks present only in the early period. LIMITATIONS: Creatinine results were not blinded, making it possible that ACE-inhibitor/placebo dosing was influenced by creatinine level. CONCLUSION: Kidney function decline is slow in HFrEF. Although random assignment to enalapril treatment results in a statistically increased risk for kidney surrogates, the risk is limited to the early phase and late eGFR slopes and risks are not different by randomly assigned group.

Change in Albuminuria and GFR as End Points for Clinical Trials in Early Stages of CKD: A Scientific Workshop Sponsored by the National Kidney Foundation in Collaboration With the US Food and Drug Administration and European Medicines Agency.

The US Food and Drug Administration (FDA) and European Medicines Agency (EMA) are currently willing to consider a 30% to 40% glomerular filtration rate (GFR) decline as a surrogate end point for kidney failure for clinical trials of kidney disease progression under appropriate conditions. However, these end points may not be practical for early stages of kidney disease. In March 2018, the National Kidney Foundation sponsored a scientific workshop in collaboration with the FDA and EMA to evaluate changes in albuminuria or GFR as candidate surrogate end points. Three parallel efforts were presented: meta-analyses of observational studies (cohorts), meta-analyses of clinical trials, and simulations of trial design. In cohorts, after accounting for measurement error, relationships between change in urinary albumin-creatinine ratio (UACR) or estimated GFR (eGFR) slope and the clinical outcome of kidney disease progression were strong and consistent. In trials, the posterior median R2 of treatment effects on the candidate surrogates with the clinical outcome was 0.47 (95% Bayesian credible interval [BCI], 0.02-0.96) for early change in UACR and 0.72 (95% BCI, 0.05-0.99) when restricted to baseline UACR>30mg/g, and 0.97 (95% BCI, 0.78-1.00) for total eGFR slope at 3 years and 0.96 (95% BCI, 0.63-1.00) for chronic eGFR slope (ie, the slope excluding the first 3 months from baseline, when there might be acute changes in eGFR). The magnitude of the relationships of changes in the candidate surrogates with risk for clinical outcome was consistent across cohorts and trials: a UACR reduction of 30% or eGFR slope reduction by 0.5 to 1.0mL/min/1.73m2 per year were associated with an HR of ∼0.7 for the clinical outcome in cohorts and trials. In simulations, using GFR slope as an end point substantially reduced the required sample size and duration of follow-up compared with the clinical end point when baseline eGFR was high, treatment effects were uniform, and there was no acute effect of the treatment. We conclude that both early change in albuminuria and GFR slope fulfill criteria for surrogacy for use as end points in clinical trials for chronic kidney disease progression under certain conditions, with stronger support for change in GFR than albuminuria. Implementation requires understanding conditions under which each surrogate is likely to perform well and restricting its use to those settings.

Using All Longitudinal Data to Define Time to Specified Percentages of Estimated GFR Decline: A Simulation Study.

RATIONALE & OBJECTIVE: The standard method to calculate time to the event of a specified percentage decline in estimated glomerular filtration rate (eGFR) uses 2 eGFR assessments, 1 at baseline and 1 at the event time. However, event times may be inaccurate due to eGFR variability and restriction of events to study visit times. We propose a novel method for calculating time to a specified percentage decline in eGFR that uses all available longitudinal eGFR assessments. STUDY DESIGN: Simulation study and comparison of methods in 2 observational cohorts. SETTINGS & PARTICIPANTS: Simulation data and study participants in the Nephrotic Syndrome Study Network (NEPTUNE) and Clinical Phenotyping and Resource Biobank Core (C-PROBE). EXPOSURE: Analytical method for calculating time to a specified percentage decline in eGFR: standard 2-point method versus a regression method incorporating all available longitudinally assessed eGFR assessments. OUTCOME: Time to percentage decline in eGFR. ANALYTIC APPROACH: A 2-point method used only the baseline eGFR and first eGFR below the decline threshold. The comparison method used ordinary linear regression incorporating all longitudinal eGFR assessments to define the baseline measure and 40% decline threshold. Time to a 40% decline in eGFR was defined as the time when the regression line crossed the decline threshold. The 2 outcome calculation methods were compared using simulations to assess the accuracy of estimated event times and power to detect event time differences between groups. Comparison of event times calculated using each method was also implemented using data from NEPTUNE and C-PROBE. RESULTS: The regression method incorporating all eGFR assessments was more accurate than the 2-point method in estimating event times in simulation analyses, particularly when eGFR variability was high, there was a greater correlation among successive eGFR values, or there were more missing data. This method was also more powerful in detecting differences between groups. Using NEPTUNE and C-PROBE data, the standard method estimated a more rapid rate of events, some likely representing transient reductions in kidney function, and was less likely to give accurate estimates in the presence of nonlinear eGFR trajectories. LIMITATIONS: Computations required for our proposed method currently limit its use to research rather than clinical applications. CONCLUSIONS: A regression method using all longitudinal eGFR values to estimate time to a percentage decline in eGFR increases accuracy and power over traditional methods, representing a potential improvement in the ability to discover treatment or biomarker effects on kidney disease progression.

Changes in Blood Pressure During Young Adulthood and Subsequent Kidney Function Decline: Findings From the Coronary Artery Risk Development in Young Adulthood (CARDIA) Study.

BACKGROUND: Many studies have focused on the association between a single blood pressure (BP) measurement and risk for adverse outcomes. However, the association of BP trajectories during young adulthood with subsequent decline in kidney function has not been well defined. STUDY DESIGN: Observational cohort study. SETTING & PARTICIPANTS: 3,429 participants in the Coronary Artery Risk Development in Young Adulthood (CARDIA) Study enrolled between the ages of 18 and 30 years. PREDICTORS: BP slope during the first 10 years of participation in CARDIA, derived from linear mixed models incorporating all repeated BP measures. OUTCOME: Decline in estimated glomerular filtration rate (eGFR) during the interval between years 10 and 20 of CARDIA participation using cystatin C measured at years 10, 15, and 20. RESULTS: Mean age of CARDIA participants at year 0 was 25.1 years, 56% were women, and 53% were white. Every 10-mmHg higher level of systolic (SBP) and diastolic BP (DBP) in year 10 was associated with change in eGFR of -0.09 (95% CI, -0.13 to -0.06) and -0.07 (95% CI, -0.12 to -0.03) mL/min/1.73m2 per year, respectively. Every 10-mmHg increase in SBP slope between years 0 and 10 was associated with a subsequent -0.52 (95% CI, -1.02 to -0.03) mL/min/1.73m2 per year change in kidney function after adjustment for comorbid conditions and SBP at year 10. Similarly, every 10-mmHg increase in DBP slope between years 0 and 10 was associated with a subsequent change in kidney function of -0.65 (95% CI, -1.23 to -0.07) mL/min/1.73m2 per year, after adjustment for comorbid conditions and DBP in year 10. LIMITATIONS: Observational design. CONCLUSIONS: During young adulthood, increasing SBP and DBP are associated with a higher rate of subsequent kidney function decline, independent of BP measured at the beginning of eGFR assessment.

Patterns of Kidney Function Decline in Autosomal Dominant Polycystic Kidney Disease: A Post Hoc Analysis From the HALT-PKD Trials.

BACKGROUND: Previous clinical studies of autosomal dominant polycystic kidney disease (ADPKD) reported that loss of kidney function usually follows a steep and relentless course. A detailed examination of individual patterns of decline in estimated glomerular filtration rate (eGFR) has not been performed. STUDY DESIGN: Longitudinal post hoc analysis of data collected during the Halt Progression of Polycystic Kidney Disease (HALT-PKD) trials. SETTING & PARTICIPANTS: 494 HALT-PKD Study A participants (younger; preserved eGFR) and 435 Study B participants (older; reduced eGFR) who had more than 3 years of follow-up and 7 or more eGFR assessments. MEASUREMENTS: Longitudinal eGFR assessments using the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) creatinine equation. PREDICTORS: Demographic, clinical, laboratory, and imaging features of participants. OUTCOMES: Probability of linear and nonlinear decline patterns or of stable eGFR calculated for each participant from a Bayesian model of individual eGFR trajectories. RESULTS: Most (62.5% in Study A and 81% in Study B) participants had a linear decline in eGFR during up to 8 years of follow-up. A proportion (22% in Study A and 13% in Study B) of progressors had a nonlinear pattern. 15.5% of participants in Study A and 6% in Study B had a prolonged (≥4.5 years) period of stable eGFRs. These individuals (Study A) had significantly smaller total kidney volumes, higher renal blood flows, lower urinary albumin excretion, and lower body mass index at baseline and study end. In Study B, participants with reduced but stable eGFRs were older than the progressors. Two-thirds of nonprogressors in both studies had PKD1 mutations, with enrichment for weak nontruncating mutations. LIMITATIONS: Relatively short follow-up of a clinical trial population. CONCLUSIONS: Although many individuals with ADPKD have a linear decline in eGFR, prolonged intervals of stable GFRs occur in a substantial fraction. Lower body mass index was associated with more stable kidney function in early ADPKD.

Estimated GFR Before and After Bariatric Surgery in CKD.

BACKGROUND: Several reviews have recently detailed the beneficial effects of weight loss surgery for kidney function. However, these studies have a number of limitations, including small sample size, few done in chronic kidney disease (CKD) stages 3 and 4, and many not including the main bariatric surgery procedures used in the United States today. STUDY DESIGN: This was an observational retrospective cohort study comparing propensity score-matched bariatric surgery patients and nonsurgery control patients who were referred for, but did not have, surgery. Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy were also compared using propensity matching. SETTING & PARTICIPANTS: Patients (714 surgery patients; 714 controls) were from a large integrated health care system, a mean of 58±8 (SD) years old, and mostly women (77%) and non-Hispanic whites (56%) and had diabetes mellitus (66%) and/or hypertension (91%). PREDICTOR: Predictors at the time of surgery or referral to surgery were age, sex, race/ethnicity, weight, and presence of diabetes and/or hypertension. OUTCOMES: The primary outcome for this study was change in estimated glomerular filtration rate (eGFR) from serum creatinine level over a median 3-year follow-up period. MEASUREMENTS: Serum creatinine was used to calculate eGFR using the CKD-EPI (CKD Epidemiology Collaboration) creatinine equation. RESULTS: Surgery patients had 9.84 (95% CI, 8.05-11.62) mL/min/1.73m2 greater eGFRs than controls at a median 3 years' follow-up and RYGB patients had 6.60 (95% CI, 3.42-9.78) mL/min/1.73m2 greater eGFRs than sleeve gastrectomy patients during the same period. LIMITATIONS: This study is limited by its nonrandomized observational study design, estimation of GFR, and large changes in muscle mass, which may affect serum creatinine level independent of changes in kidney function. CONCLUSIONS: Bariatric surgery, especially the RYGB procedure, results in significant improvements for up to 3 years in eGFRs for patients with CKD stages 3 and 4.

von Willebrand Factor, ADAMTS13 Activity, and Decline in Kidney Function: A Population-Based Cohort Study.

BACKGROUND: Altered levels of von Willebrand factor (vWF) and ADAMTS13 can promote thrombosis and disturb blood flow in kidney microcirculations. We investigated the association of serum vWF:ADAMTS13 ratio in relation to decline in kidney function. STUDY DESIGN: Prospective cohort study. SETTING & PARTICIPANTS: 2,479 individuals (mean age, 65.1±5.9 [SD] years; 43% men) from the population-based Rotterdam Study. PREDICTORS: vWF, ADAMTS13, and vWF:ADAMTS13 ratio. OUTCOMES & MEASUREMENTS: Annual decline in estimated glomerular filtration rate (eGFR), halving of eGFR, and new-onset eGFR<60mL/min/1.73m2 were assessed. RESULTS: During a median follow-up of 11 (range, 7.81-13.57) years, 500 cases of new-onset eGFR<60mL/min/1.73m2 occurred. The population had a mean eGFR decline of 0.96±0.92mL/min/1.73m2 per year. Higher vWF:ADAMTS13 ratio was associated with steeper annual decline in eGFR (difference, -0.06 [95% CI, -0.09 to -0.02] mL/min/1.73m2 per year) and higher risk for new-onset eGFR<60mL/min/1.73m2 (OR, 1.13; 95% CI, 1.01-1.27). Likewise, higher vWF:ADAMTS13 ratio was associated with higher risk for halving of eGFR (OR, 1.40; 95% CI, 1.02-1.93). After adjustment for cardiovascular risk factors and blood group, effect estimates remained the same. LIMITATIONS: No data available for albuminuria. Participants were classified based on a single measurement of vWF and ADAMTS13. CONCLUSIONS: In this population-based study, we showed that higher vWF:ADAMTS13 ratio is associated with decline in kidney function, suggesting a role of elevated prothrombotic factors in the development and progression of kidney disease.

Arteriovenous fistula creation may slow estimated glomerular filtration rate trajectory.

BACKGROUND: We practice the timely placement of an arteriovenous fistula (AVF) in patients facing chronic hemodialysis. We have anecdotally observed after AVF creation that there appears to be a slowing of the decline in kidney function as measured by the estimated glomerular filtration rate (eGFR). There are physiologically plausible explanations as to how an AVF might alter kidney function, but this clinical observation has been attributed to improved compliance and/or other practices. The present retrospective observational analysis was performed to assess the possibility that a successfully created AVF could be associated with the slowing of the eGFR trajectory. METHODS: We identified 123 patients between 2005 and 2010 with at least two eGFR determinations for 2 years before and up to 2 years after AVF creation. Inclusion eligibility was that the fistula was maturing by the nephrologists' initial post-creation examination. Termination events were death, starting dialysis or transplantation. Each subject served as their own control for the pre- and post-AVF-creation eGFR measurements. RESULTS: Subjects' median age was 68 years and 56% were diabetic. The rate of change of the eGFR for the 2 years prior to AVF creation was -5.9 mL/min/year (95% CI: -5.3, -6.5) and after AVF creation -0.5 mL/min/year (95% CI: -1.1, 0.1) (interaction (P < 0.001). CONCLUSIONS: A functioning AVF may be associated with a slowing of the eGFR decline. Agreeing to timely AVF creation selects patients in an otherwise typical population and other confounders have not yet been eliminated. To do so a thorough prospective observational study is indicated.

GFR decline as an end point for clinical trials in CKD: a scientific workshop sponsored by the National Kidney Foundation and the US Food and Drug Administration.

The US Food and Drug Administration currently accepts halving of glomerular filtration rate (GFR), assessed as doubling of serum creatinine level, as a surrogate end point for the development of kidney failure in clinical trials of kidney disease progression. A doubling of serum creatinine level generally is a late event in chronic kidney disease (CKD); thus, there is great interest in considering alternative end points for clinical trials to shorten their duration, reduce sample size, and extend their conduct to patients with earlier stages of CKD. However, the relationship between lesser declines in GFR and the subsequent development of kidney failure has not been well characterized. The National Kidney Foundation and Food and Drug Administration sponsored a scientific workshop to critically examine available data to determine whether alternative GFR-based end points have sufficiently strong relationships with important clinical outcomes of CKD to be used in clinical trials. Based on a series of meta-analyses of cohorts and clinical trials and simulations of trial designs and analytic methods, the workshop concluded that a confirmed decline in estimated GFR of 30% over 2 to 3 years may be an acceptable surrogate end point in some circumstances, but the pattern of treatment effects on GFR must be examined, specifically acute effects on estimated GFR. An estimated GFR decline of 40% may be more broadly acceptable than a 30% decline across a wider range of baseline GFRs and patterns of treatment effects on GFR. However, there are other circumstances in which these end points could lead to a reduction in statistical power or erroneous conclusions regarding benefits or harms of interventions. We encourage careful consideration of these alternative end points in the design of future clinical trials.

GFR decline as an alternative end point to kidney failure in clinical trials: a meta-analysis of treatment effects from 37 randomized trials.

BACKGROUND: There is increased interest in using alternative end points for trials of kidney disease progression. The currently established end points of end-stage renal disease and doubling of serum creatinine level, equivalent to a 57% decline in estimated glomerular filtration rate (eGFR), are late events in chronic kidney disease (CKD), requiring large clinical trials with long follow-up. As part of a comprehensive evaluation of lesser declines in eGFR as alternative end points, we describe the consistency of treatment effects of intervention on the alternative and established end points in past trials. STUDY DESIGN: Diagnostic test study. SETTING & POPULATION: 9,488 participants from 37 randomized controlled trials of CKD progression across 5 intervention types. INDEX TEST: Alternative end points including percentage change in eGFR from baseline (20%, 30%, 40%, and 57%) throughout study duration and to 12, 18, and 24 months. eGFR change confirmed versus nonconfirmed at the next visit. REFERENCE TEST: The historically established end point of time to composite of treated kidney failure (end-stage renal disease), untreated kidney failure (GFR<15mL/min/1.73m(2)), or doubling of serum creatinine level throughout study duration. RESULTS: Over a median of 3.62 years' follow-up, there were 3,070 established end points. Compared to the established end point, the number of alternative end points was greater for smaller versus larger declines in eGFR and longer versus shorter follow-up intervals. There was a general trend toward attenuation of the treatment effect with end points defined by a lesser eGFR decline, with greater attenuation with nonconfirmed end points, except for the low-protein-diet intervention, for which a stronger treatment effect was observed. The ratio (95% credible interval) of the HR for the alternative to established end point for the 5 intervention types ranged from 0.91 (0.64-1.43) to 1.12 (0.89-1.40) for 40% decline and from 0.88 (0.63-1.39) to 1.15 (0.88-1.54) for 30% decline for the overall study duration, indicating consistency of treatment effects. LIMITATIONS: Limited variety of interventions tested and low statistical power for many CKD clinical trials. CONCLUSIONS: These results provide some support for the use of lesser eGFR declines as a surrogate end point, with stronger support for the 40% than 30% decline.