Development and Validation of the American Heart Association's PREVENT Equations.

BACKGROUND: Multivariable equations are recommended by primary prevention guidelines to assess absolute risk of cardiovascular disease (CVD). However, current equations have several limitations. Therefore, we developed and validated the American Heart Association Predicting Risk of CVD EVENTs (PREVENT) equations among US adults 30 to 79 years of age without known CVD. METHODS: The derivation sample included individual-level participant data from 25 data sets (N=3 281 919) between 1992 and 2017. The primary outcome was CVD (atherosclerotic CVD and heart failure). Predictors included traditional risk factors (smoking status, systolic blood pressure, cholesterol, antihypertensive or statin use, and diabetes) and estimated glomerular filtration rate. Models were sex-specific, race-free, developed on the age scale, and adjusted for competing risk of non-CVD death. Analyses were conducted in each data set and meta-analyzed. Discrimination was assessed using the Harrell C-statistic. Calibration was calculated as the slope of the observed versus predicted risk by decile. Additional equations to predict each CVD subtype (atherosclerotic CVD and heart failure) and include optional predictors (urine albumin-to-creatinine ratio and hemoglobin A1c), and social deprivation index were also developed. External validation was performed in 3 330 085 participants from 21 additional data sets. RESULTS: Among 6 612 004 adults included, mean±SD age was 53±12 years, and 56% were women. Over a mean±SD follow-up of 4.8±3.1 years, there were 211 515 incident total CVD events. The median C-statistics in external validation for CVD were 0.794 (interquartile interval, 0.763-0.809) in female and 0.757 (0.727-0.778) in male participants. The calibration slopes were 1.03 (interquartile interval, 0.81-1.16) and 0.94 (0.81-1.13) among female and male participants, respectively. Similar estimates for discrimination and calibration were observed for atherosclerotic CVD- and heart failure-specific models. The improvement in discrimination was small but statistically significant when urine albumin-to-creatinine ratio, hemoglobin A1c, and social deprivation index were added together to the base model to total CVD (ΔC-statistic [interquartile interval] 0.004 [0.004-0.005] and 0.005 [0.004-0.007] among female and male participants, respectively). Calibration improved significantly when the urine albumin-to-creatinine ratio was added to the base model among those with marked albuminuria (>300 mg/g; 1.05 [0.84-1.20] versus 1.39 [1.14-1.65]; P=0.01). CONCLUSIONS: PREVENT equations accurately and precisely predicted risk for incident CVD and CVD subtypes in a large, diverse, and contemporary sample of US adults by using routinely available clinical variables.

Proteomics: Progress and Promise of High-Throughput Proteomics in Chronic Kidney Disease.

Current proteomic tools permit the high-throughput analysis of the blood proteome in large cohorts, including those enriched for chronic kidney disease (CKD) or its risk factors. To date, these studies have identified numerous proteins associated with cross-sectional measures of kidney function, as well as with the longitudinal risk of CKD progression. Representative signals that have emerged from the literature include an association between levels of testican-2 and favorable kidney prognosis and an association between levels of TNFRSF1A and TNFRSF1B and worse kidney prognosis. For these and other associations, however, understanding whether the proteins play a causal role in kidney disease pathogenesis remains a fundamental challenge, especially given the strong impact that kidney function can have on blood protein levels. Prior to investing in dedicated animal models or randomized trials, methods that leverage the availability of genotyping in epidemiologic cohorts-including Mendelian randomization, colocalization analyses, and proteome-wide association studies-can add evidence for causal inference in CKD proteomics research. In addition, integration of large-scale blood proteome analyses with urine and tissue proteomics, as well as improved assessment of posttranslational protein modifications (e.g., carbamylation), represent important future directions. Taken together, these approaches seek to translate progress in large-scale proteomic profiling into the promise of improved diagnostic tools and therapeutic target identification in kidney disease.

Association of Low Glomerular Filtration Rate With Adverse Outcomes at Older Age in a Large Population With Routinely Measured Cystatin C.

BACKGROUND: The commonly accepted threshold of glomerular filtration rate (GFR) to define chronic kidney disease (CKD) is less than 60 mL/min/1.73 m2. This threshold is based partly on associations between estimated GFR (eGFR) and the frequency of adverse outcomes. The association is weaker in older adults, which has created disagreement about the appropriateness of the threshold for these persons. In addition, the studies measuring these associations included relatively few outcomes and estimated GFR on the basis of creatinine level (eGFRcr), which may be less accurate in older adults. OBJECTIVE: To evaluate associations in older adults between eGFRcr versus eGFR based on creatinine and cystatin C levels (eGFRcr-cys) and 8 outcomes. DESIGN: Population-based cohort study. SETTING: Stockholm, Sweden, 2010 to 2019. PARTICIPANTS: 82 154 participants aged 65 years or older with outpatient creatinine and cystatin C testing. MEASUREMENTS: Hazard ratios for all-cause mortality, cardiovascular mortality, and kidney failure with replacement therapy (KFRT); incidence rate ratios for recurrent hospitalizations, infection, myocardial infarction or stroke, heart failure, and acute kidney injury. RESULTS: The associations between eGFRcr-cys and outcomes were monotonic, but most associations for eGFRcr were U-shaped. In addition, eGFRcr-cys was more strongly associated with outcomes than eGFRcr. For example, the adjusted hazard ratios for 60 versus 80 mL/min/1.73 m2 for all-cause mortality were 1.2 (95% CI, 1.1 to 1.3) for eGFRcr-cys and 1.0 (CI, 0.9 to 1.0) for eGFRcr, and for KFRT they were 2.6 (CI, 1.2 to 5.8) and 1.4 (CI, 0.7 to 2.8), respectively. Similar findings were observed in subgroups, including those with a urinary albumin-creatinine ratio below 30 mg/g. LIMITATION: No GFR measurements. CONCLUSION: Compared with low eGFRcr in older patients, low eGFRcr-cys was more strongly associated with adverse outcomes and the associations were more uniform. PRIMARY FUNDING SOURCE: Swedish Research Council, National Institutes of Health, and Dutch Kidney Foundation.

Serum and Urine Metabolites and Kidney Function.

BACKGROUND: Metabolites represent a read-out of cellular processes underlying states of health and disease. METHODS: We evaluated cross-sectional and longitudinal associations between 1255 serum and 1398 urine known and unknown (denoted with "X" in name) metabolites (Metabolon HD4, 721 detected in both biofluids) and kidney function in 1612 participants of the Atherosclerosis Risk in Communities (ARIC) Study. All analyses were adjusted for clinical and demographic covariates, including for baseline eGFR and UACR in longitudinal analyses. RESULTS: At visit 5 of the ARIC study, the mean age of participants was 76 years (SD 6), 56% were women, mean eGFR was 62 ml/min/1.73m2 (SD 20), and median urine albumin-to-creatinine level (UACR) was 13 mg/g (IQR 25). In cross-sectional analysis, 675 serum and 542 urine metabolites were associated with eGFR (Bonferroni-corrected p < 4.0E-5 for serum analyses and p < 3.6E-5 for urine analyses), including 248 metabolites shared across biofluids. Fewer metabolites (75 serum and 91 urine metabolites, including 7 shared across biofluids) were cross-sectionally associated with albuminuria. Guanidinosuccinate, N2,N2-dimethylguanosine, hydroxy-N6,N6,N6-trimethyllysine, X-13844, and X-25422 were significantly associated with both eGFR and albuminuria. Over a mean follow-up of 6.6 years, serum mannose (HR 2.3 [1.6,3.2], p = 2.7E-5) and urine X-12117 (HR 1.7 [1.3,2.2], p = 1.9E-5) were risk factors for UACR doubling, whereas urine sebacate (HR 0.86 [0.80,0.92], p = 1.9E-5) was inversely associated. Compared to clinical characteristics alone, including the top 5 endogenous metabolites in serum and urine associated with longitudinal outcomes improved the outcome prediction (AUCs for eGFR decline: clinical model = 0.79, clinical + metabolites model = 0.87, p = 8.1E-6; for UACR doubling: clinical model = 0.66, clinical + metabolites model = 0.73, p = 2.9E-5). CONCLUSIONS: Metabolomic profiling in different biofluids provided distinct and potentially complementary insights into the biology and prognosis of kidney diseases.

Associations of Apixaban Dose With Safety and Effectiveness Outcomes in Patients With Atrial Fibrillation and Severe Chronic Kidney Disease.

BACKGROUND: Recommendations for apixaban dosing on the basis of kidney function are inconsistent between the US Food and Drug Administration and European Medicines Agency for patients with atrial fibrillation. Optimal apixaban dosing in chronic kidney disease remains unknown. METHODS: With the use of deidentified electronic health record data from the Optum Labs Data Warehouse, patients with atrial fibrillation and chronic kidney disease stage 4/5 initiating apixaban between 2013 and 2021 were identified. Risks of bleeding and stroke/systemic embolism were compared by apixaban dose (5 versus 2.5 mg), adjusted for baseline characteristics by the inverse probability of treatment weighting. The Fine-Gray subdistribution hazard model was used to account for the competing risk of death. Cox regression was used to examine risk of death by apixaban dose. RESULTS: Among 4313 apixaban new users, 1705 (40%) received 5 mg and 2608 (60%) received 2.5 mg. Patients treated with 5 mg apixaban were younger (mean age, 72 versus 80 years), with greater weight (95 versus 80 kg) and higher serum creatinine (2.7 versus 2.5 mg/dL). Mean estimated glomerular filtration rate was not different between the groups (24 versus 24 mL·min-1·1.73 m-2). In inverse probability of treatment weighting analysis, apixaban 5 mg was associated with a higher risk of bleeding (incidence rate 4.9 versus 2.9 events per 100 person-years; incidence rate difference, 2.0 [95% CI, 0.6-3.4] events per 100 person-years; subdistribution hazard ratio, 1.63 [95% CI, 1.04-2.54]). There was no difference between apixaban 5 mg and 2.5 mg groups in the risk of stroke/systemic embolism (3.3 versus 3.0 events per 100 person-years; incidence rate difference, 0.2 [95% CI, -1.0 to 1.4] events per 100 person-years; subdistribution hazard ratio, 1.01 [95% CI, 0.59-1.73]), or death (9.9 versus 9.4 events per 100 person-years; incidence rate difference, 0.5 [95% CI, -1.6 to 2.6] events per 100 person-years; hazard ratio, 1.03 [95% CI, 0.77-1.38]). CONCLUSIONS: Compared with 2.5 mg, use of 5 mg apixaban was associated with a higher risk of bleeding in patients with atrial fibrillation and severe chronic kidney disease, with no difference in the risk of stroke/systemic embolism or death, supporting the apixaban dosing recommendations on the basis of kidney function by the European Medicines Agency, which differ from those issued by the US Food and Drug Administration.

New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race.

BACKGROUND: Current equations for estimated glomerular filtration rate (eGFR) that use serum creatinine or cystatin C incorporate age, sex, and race to estimate measured GFR. However, race in eGFR equations is a social and not a biologic construct. METHODS: We developed new eGFR equations without race using data from two development data sets: 10 studies (8254 participants, 31.5% Black) for serum creatinine and 13 studies (5352 participants, 39.7% Black) for both serum creatinine and cystatin C. In a validation data set of 12 studies (4050 participants, 14.3% Black), we compared the accuracy of new eGFR equations to measured GFR. We projected the prevalence of chronic kidney disease (CKD) and GFR stages in a sample of U.S. adults, using current and new equations. RESULTS: In the validation data set, the current creatinine equation that uses age, sex, and race overestimated measured GFR in Blacks (median, 3.7 ml per minute per 1.73 m2 of body-surface area; 95% confidence interval [CI], 1.8 to 5.4) and to a lesser degree in non-Blacks (median, 0.5 ml per minute per 1.73 m2; 95% CI, 0.0 to 0.9). When the adjustment for Black race was omitted from the current eGFR equation, measured GFR in Blacks was underestimated (median, 7.1 ml per minute per 1.73 m2; 95% CI, 5.9 to 8.8). A new equation using age and sex and omitting race underestimated measured GFR in Blacks (median, 3.6 ml per minute per 1.73 m2; 95% CI, 1.8 to 5.5) and overestimated measured GFR in non-Blacks (median, 3.9 ml per minute per 1.73 m2; 95% CI, 3.4 to 4.4). For all equations, 85% or more of the eGFRs for Blacks and non-Blacks were within 30% of measured GFR. New creatinine-cystatin C equations without race were more accurate than new creatinine equations, with smaller differences between race groups. As compared with the current creatinine equation, the new creatinine equations, but not the new creatinine-cystatin C equations, increased population estimates of CKD prevalence among Blacks and yielded similar or lower prevalence among non-Blacks. CONCLUSIONS: New eGFR equations that incorporate creatinine and cystatin C but omit race are more accurate and led to smaller differences between Black participants and non-Black participants than new equations without race with either creatinine or cystatin C alone. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases.).

Associations of Baseline and Longitudinal Serum Uromodulin With Kidney Failure and Mortality: Results From the African American Study of Kidney Disease and Hypertension (AASK) Trial.

RATIONALE & OBJECTIVE: Uromodulin (UMOD) is the most abundant protein found in urine and has emerged as a promising biomarker of tubule health. Circulating UMOD is also detectable, but at lower levels. We evaluated whether serum UMOD levels were associated with the risks of incident kidney failure with replacement therapy (KFRT) and mortality. STUDY DESIGN: Prospective cohort. SETTING & PARTICIPANTS: Participants in AASK (the African American Study of Kidney Disease and Hypertension) with available stored serum samples from the 0-, 12-, and 24-month visits for biomarker measurement. PREDICTORS: Baseline log-transformed UMOD and change in UMOD over 2 years. OUTCOMES: KFRT and mortality. ANALYTICAL APPROACH: Cox proportional hazards and mixed-effects models. RESULTS: Among 500 participants with baseline serum UMOD levels (mean age, 54y; 37% female), 161 KFRT events occurred during a median of 8.5 years. After adjusting for baseline demographic factors, clinical factors, glomerular filtration rate, log-transformed urine protein-creatinine ratio, and randomized treatment groups, a 50% lower baseline UMOD level was independently associated with a 35% higher risk of KFRT (adjusted HR, 1.35; 95% CI, 1.07-1.70). For annual UMOD change, each 1-standard deviation lower change was associated with a 67% higher risk of KFRT (adjusted HR, 1.67; 95% CI, 1.41-1.99). Baseline UMOD and UMOD change were not associated with mortality. UMOD levels declined more steeply for metoprolol versus ramipril (P<0.001) as well as for intensive versus standard blood pressure goals (P = 0.002). LIMITATIONS: Small sample size and limited generalizability. CONCLUSIONS: Lower UMOD levels at baseline and steeper declines in UMOD over time were associated with a higher risk of subsequent KFRT in a cohort of African American adults with chronic kidney disease and hypertension. PLAIN-LANGUAGE SUMMARY: Prior studies of uromodulin (UMOD), the most abundant protein in urine, and kidney disease have focused primarily on urinary UMOD levels. The present study evaluated associations of serum UMOD levels with the risks of kidney failure with replacement therapy (KFRT) and mortality in a cohort of African American adults with hypertension and chronic kidney disease. It found that participants with lower levels of UMOD at baseline were more likely to experience KFRT even after accounting for baseline kidney measures. Similarly, participants who experienced steeper annual declines in UMOD also had a heightened risk of kidney failure. Neither baseline nor annual change in UMOD was associated with mortality. Serum UMOD is a promising biomarker of kidney health.

Extreme Humid-Heat Exposure and Mortality Among Patients Receiving Dialysis.

RATIONALE & OBJECTIVE: Exposure to extreme heat events has been linked to increased morbidity and mortality in the general population. Patients receiving maintenance dialysis may be vulnerable to greater risks from these events, but this is not well understood. We sought to characterize the association of extreme heat events and the risk of death among patients receiving dialysis in the United States. STUDY DESIGN: Retrospective cohort study. SETTING & PARTICIPANTS: Data from the United States Renal Data System were used to identify adults living in US urban settlements prone to extreme heat who initiated maintenance dialysis between 1997 and 2016. EXPOSURE: An extreme heat event was defined as a time-updated heat index (a humid-heat metric) exceeding 40.6°C for ≥2 days or 46.1°C for ≥1 day. OUTCOME: Death. ANALYTICAL APPROACH: Cox proportional hazards regression to estimate the elevation in risk of death during a humid-heat event adjusted for age, sex, year of dialysis initiation, dialysis modality, poverty level, and climate region. Interactions between humid-heat and these same factors were explored. RESULTS: Among 945,251 adults in 245 urban settlements, the mean age was 63 years and 44% were female. During a median follow-up of 3.6 years, 498,049 adults were exposed to at least one of 7,154 extreme humid-heat events, and 500,025 deaths occurred. In adjusted models, there was an increased risk of death (hazard ratio 1.18; 95% confidence interval 1.15-1.20) during extreme humid-heat exposure. Relative mortality risk was higher among patients living in the Southeast (P<0.001) compared with the Southwest. LIMITATIONS: Possibility of exposure misclassification, did not account for land use and air pollution co-exposures. CONCLUSIONS: This study suggests that patients receiving dialysis face an increased risk of death during extreme humid-heat exposure.

Associations of Urine and Plasma Metabolites with Kidney Failure and Death in a CKD Cohort.

RATIONALE & OBJECTIVE: Biomarkers that enable better identification of persons with chronic kidney disease (CKD) who are at higher risk for disease progression and adverse events are needed. This study sought to identify urine and plasma metabolites associated with progression of kidney disease. STUDY DESIGN: Prospective metabolome-wide association study. SETTING & PARTICIPANTS: Persons with CKD enrolled in the German CKD Study (GCKD) with metabolite measurements; with external validation within the Atherosclerosis Risk in Communities Study. EXPOSURES: 1,513 urine and 1,416 plasma metabolites (Metabolon, Inc.) measured at study entry using untargeted mass spectrometry. OUTCOMES: Main endpoints were kidney failure (KF), and a composite endpoint of KF, eGFR <15 mL/min/1.73m2, or 40% decline in eGFR (CKE). Death from any cause was a secondary endpoint. After a median of 6.5 years follow-up, 500 persons experienced KF, 1,083 experienced CKE and 680 died. ANALYTICAL APPROACH: Time-to-event analyses using multivariable proportional hazard regression models in a discovery-replication design, with external validation. RESULTS: 5,088 GCKD participants were included in analyses of urine metabolites and 5,144 in analyses of plasma metabolites. Among 182 unique metabolites, 30 were significantly associated with KF, 49 with CKE, and 163 with death. The strongest association with KF was observed for plasma hydroxyasparagine (hazard ratio: 1.95, 95% confidence interval: 1.68-2.25). An unnamed metabolite measured in plasma and urine was significantly associated with KF, CKE, and death. External validation of the identified associations of metabolites with KF or CKE revealed direction-consistency for 88% of observed associations. Selected associations of 18 metabolites with study outcomes have not been previously reported. LIMITATIONS: Use of observational data and semi-quantitative metabolite measurements at a single time point. CONCLUSIONS: The observed associations between metabolites and KF, CKE or death in persons with CKD confirmed previously reported findings and also revealed several associations not previously described. These findings warrant confirmatory research in other study cohorts.

Dihydropyridine Calcium Channel Blockers and Kidney Outcomes.

BACKGROUND: Early trials of dihydropyridine calcium channel blockers (DCCBs) suggest a detrimental effect on intraglomerular pressure and an association with albuminuria. OBJECTIVE: We sought to evaluate the associations of DCCB initiation with albuminuria and kidney failure with replacement therapy (KFRT) and to determine whether renin-angiotensin system (RAS) blockade modified these associations. DESIGN: We conducted a target trial emulation study using a new user, active comparator design and electronic health record data from Geisinger Health. PARTICIPANTS: We included patients without severe albuminuria or KFRT who were initiated on a DCCB or thiazide (active comparator) between January 1, 2004, and December 31, 2019. MAIN MEASURES: Using inverse probability of treatment weighting, we performed doubly robust Cox proportional hazards regression to estimate the association of DCCB initiation with incident severe albuminuria (urine albumin to creatinine ratio > 300 mg/g) and KFRT, overall and stratified by RAS blocker use. KEY RESULTS: There were 11,747 and 26,758 eligible patients initiating a DCCB and thiazide, respectively, with a weighted baseline mean age of 60 years, systolic blood pressure of 143 mm Hg, and eGFR of 86 mL/min/1.73 m2, and with a mean follow-up of 8 years. Compared with thiazides, DCCBs were significantly associated with the development of severe albuminuria (hazard ratio [HR], 1.29; 95% confidence interval [CI], 1.16-1.43), with attenuation of risk in the presence of RAS blockade (P for interaction < 0.001). The risk of KFRT was increased among patients without RAS blockade (HR, 1.66; 95% CI, 1.19-2.31), but not with RAS blockade (P for interaction = 0.005). CONCLUSIONS: DCCBs were associated with increased risk of albuminuria and, in the absence of RAS blockade, KFRT. These findings suggest coupling DCCB therapy with RAS blockade may mitigate adverse kidney outcomes.

Glucagon-like peptide-1 receptor agonists and the risk of atrial fibrillation in adults with diabetes: a real-world study.

BACKGROUND: Glucagon-like peptide-1 receptor agonists (GLP-1RA) have cardiovascular benefits in type 2 diabetes, but none of the cardiovascular trials studied atrial fibrillation/atrial flutter (AF) as a primary endpoint. Data from post-marketing surveillance studies remains sparse. OBJECTIVE: To examine the real-world risk of AF comparing GLP-1RA with other non-insulin glucose-lowering agents. DESIGN: Cohort study using de-identified electronic health record data from the Optum Labs Data Warehouse. PARTICIPANTS: Adult patients with diabetes who were newly prescribed add-on non-insulin glucose-lowering agents and were on metformin between 2005-2020. EXPOSURES: New users of GLP-1RA were separately compared with new users of dipeptidyl peptidase-4 inhibitors (DPP4i) and sodium-glucose cotransporter 2 inhibitors (SGLT2i), using 1:1 propensity score matching to adjust for differences in patient characteristics. MAIN MEASURES: The primary outcome was incident AF, defined and captured by diagnosis code for AF. Incidence rate difference (IRD) and hazard ratio (HR) were estimated in the matched cohorts. KEY RESULTS: In the matched cohort of 14,566 pairs of GLP-1RA and DPP4i followed for a median of 3.8 years, GLP-1RA use was associated with a lower risk of AF (IRD, -1.0; 95% CI, -1.8 to -0.2 per 1000 person-years; HR, 0.82; 95% CI, 0.70 to 0.96). In the matched cohort of 9,424 pairs of patients on GLP-1RA and SGLT2i with a median follow-up of 2.9 years, there was no difference in the risk for AF (IRD, 0.4; 95% CI -0.7 to 1.5 per 1000 person-years; HR, 1.12; 95% CI, 0.89 to 1.42). CONCLUSIONS: In this real-word study, GLP-1RA was associated with a lower risk of AF compared with DPP4i, but no difference compared with SGLT2i, suggesting that cardiovascular benefits of GLP-1RA use may extend to prevention for AF in patients with diabetes. Our findings call for future randomized controlled trials to focus on the effects of GLP-1RA on AF prevention.

Association of Sevelamer Initiation with Gastrointestinal Bleeding Hospitalization in Individuals Requiring Hemodialysis.

Introduction Case reports have suggested a causative role between sevelamer use and subsequent gastrointestinal bleeding (GIB), but no large observational studies have evaluated this association. Methods Using the United States Renal Data System database from 2015 to 2019, we examined the association between initiation of sevelamer (versus non-sevelamer containing phosphate binders) and GIB hospitalization as well as all-cause mortality among individuals on hemodialysis. We emulated a target trial using Cox regression models and inverse probability of treatment weights to estimate the adjusted hazard ratios (HR) across outcomes and subgroups. Results Among 21,354 new users of phosphate binders (11,276 sevelamer and 10,078 non-sevelamer) with baseline lab data (calcium, phosphorus, hemoglobin, and albumin), there were 2,811 GIB hospitalizations and 5,920 deaths after a median follow-up of 1.3 years. Compared with the initiation of non-sevelamer binders, sevelamer was not associated with an increased risk of GIB hospitalization (89 vs. 90 events per 1000 person-years; IPTW-HR 0.98, 95% CI 0.91 - 1.06) or all-cause mortality (220 vs. 224 events per 1000 person-years; IPTW-HR 0.98 95% CI 0.93 - 1.03). Subgroup analyses (such as diabetes and anti-coagulation use) were generally consistent, and there was no association between sevelamer dose and GIB hospitalization. Conclusion Among patients requiring hemodialysis, sevelamer (vs non-sevelamer) containing phosphate binders was not associated with increased risk of GIB hospitalization.

Accuracy of GFR estimating equations based on creatinine, cystatin C or both in routine care.

BACKGROUND: New equations to estimate glomerular filtration rate based on creatinine (eGFRcr), cystatin C (eGFRcys) or both (eGFRcr-cys) have been developed by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and the European Kidney Function Consortium (EKFC). There is a need to evaluate the performance of these equations in diverse European settings to inform implementation decisions, especially among people with key comorbid conditions. METHODS: We performed a cross-sectional study including 6174 adults referred for single-point plasma clearance of iohexol in Stockholm, Sweden, with 9579 concurrent measurements of creatinine and cystatin C. We assessed the performance of the CKD-EPI 2009/2012/2021, EKFC 2021/2023, revised Lund-Malmö (RLM) 2011 and Caucasian, Asian, Pediatric and Adult (CAPA) 2014 equations against measured GFR (mGFR). RESULTS: Mean age was 56 years, median mGFR was 62 mL/min/1.73 m2 and 40% were female. Comorbid conditions were common: cardiovascular disease (30%), liver disease (28%), diabetes (26%) and cancer (26%). All eGFRcr-cys equations had small bias and P30 (the percentage of estimated values within 30% of mGFR) close to 90%, and performed better than eGFRcr or eGFRcys equations. Among eGFRcr equations, CKD-EPI 2009 and CKD-EPI 2021 showed larger bias and lower P30 than EKFC 2021 and RLM. There were no meaningful differences in performance across eGFRcys equations. Findings were consistent across comorbid conditions, and eGFRcr-cys equations showed good performance in patients with liver disease, cancer and heart failure. CONCLUSIONS: In conclusion, eGFRcr-cys equations performed best, with minimal variation among equations in this Swedish cohort. The lower performance of CKD-EPI eGFRcr equations compared with EKFC and RLM may reflect differences in population characteristics and mGFR methods. Implementing eGFRcr equations will require a trade-off between accuracy and uniformity across regions.

Comparative CKD risk prediction using homocitrulline and carbamylated albumin: two circulating markers of protein carbamylation.

BACKGROUND: Protein carbamylation, a post-translational protein modification primarily driven by urea, independently associates with adverse clinical outcomes in patients with CKD. Biomarkers used to quantify carbamylation burden have mainly included carbamylated albumin (C-Alb) and homocitrulline (HCit, carbamylated lysine). In this study, we aimed to compare the prognostic utility of these two markers in order to facilitate comparisons of existing studies employing either marker alone, and to inform future carbamylation studies. METHODS: Both serum C-Alb and free HCit levels were assayed from the same timepoint in 1632 individuals with CKD stages 2-4 enrolled in the prospective Chronic Renal Insufficiency Cohort (CRIC) study. Adjusted Cox proportional hazard models were used to assess risks for the outcomes of death (primary) and end stage kidney disease (ESKD) using each marker. C-statistics, net reclassification improvement, and integrated discrimination improvement were used to compare the prognostic value of each marker. RESULTS: Participant demographics included mean (SD) age 59 (11) years; 702 (43%) females; 700 (43%) white. C-Alb and HCit levels were positively correlated with one another (Pearson correlation coefficient 0.64). Higher C-Alb and HCit levels showed similar increased risk of death (e.g., the adjusted hazard ratio [HR] for death in the 4th carbamylation quartile compared to the 1st was 1.90 (95% confidence interval [CI] 1.35-2.66) for C-Alb, and 1.89 [1.27-2.81] for HCit; and on a continuous scale, the adjusted HR for death using C-Alb was 1.24 [1.11 to 1.39] per standard deviation increase, and 1.27 [1.10-1.46] using HCit). Both biomarkers also had similar HRs for ESKD. The C-statistics were similar when adding each carbamylation biomarker to base models (e.g., for mortality models, the C-statistic was 0.725 [0.707-0.743] with C-Alb and 0.725 [0.707-0.743] with HCit, both compared to a base model 0.723). Similarities were also observed for the net reclassification improvement and integrated discrimination improvement metrics. CONCLUSIONS: C-Alb and HCit had similar performance across multiple prognostic assessments. The markers appear readily comparable in CKD epidemiological studies.

A Novel Creatinine Muscle Index Based on Creatinine Filtration: Associations with Frailty and Mortality.

SIGNIFICANCE STATEMENT: Low muscle mass is related to frailty and increased mortality in older adults. However, muscle mass is not easily assessed in routine clinical practice. This paper describes a novel creatinine muscle index (CMI) on the basis of serum creatinine and cystatin C. CMI was moderately associated with frailty among older adults. A significantly higher proportion of individuals with weak grip strength were in the lowest tertile of CMI. The index was also associated with mortality. These results are consistent with the hypothesis that creatinine filtration may be an index of muscle mass, which may have utility in clinical practice. BACKGROUND: Low muscle mass is related to frailty and increased mortality in older adults. However, muscle mass is not easily assessed in routine clinical practice. METHODS: This study describes a novel creatinine muscle index (CMI) on the basis of serum creatinine and cystatin C in a community-based sample of older adults from the Atherosclerosis Risk in Communities Study. Analyses included 4639 participants who attended visit 5 (2011-2013) and 12,786 participants who attended visit 2 (1990-1992). CMI was defined as creatinine filtration (the product of serum creatinine times eGFR on the basis of cystatin C) and was analyzed in sex-specific tertiles. Cross-sectional associations of CMI with a frailty trichotomy, defined by the number (robust [0]/prefrail [1-2]/frail [3-5]) of five frailty components (weight loss, slowness, exhaustion, weakness, and low physical activity), were studied using polychotomous logistic regression and binary logistic regression with each frailty component. Cox regression was used to estimate associations of CMI at visit 5 and visit 2 with mortality. Models were adjusted for demographics, clinical variables, and comorbid conditions. RESULTS: CMI (tertile 1 versus 3) was moderately associated with frailty (visit 5: adjusted odds ratio 4.23 [95% confidence interval (CI), 2.02 to 8.87] in men and 2.34 [95% CI, 1.41 to 3.89] in women) and with mortality (visit 5: adjusted hazard ratio 1.45 [95% CI, 1.08 to 1.94] in men and 1.55 [95% CI, 1.13 to 2.12] in women; similar results were seen at visit 2). CONCLUSION: Lower CMI was associated with frailty and increased mortality, two clinical outcomes known to be associated with decreased muscle mass. Creatinine filtration may be an index of muscle mass and have utility in clinical practice, particularly at low levels.

Accuracy of GFR Estimating Equations in Patients with Discordances between Creatinine and Cystatin C-Based Estimations.

SIGNIFICANCE STATEMENT: Large discordances between eGFR on the basis of creatinine (eGFR cr ) or cystatin C (eGFR cys ) are common in clinical practice. However, which GFR estimating equation (eGFR cr , eGFR cys , or eGFR cr-cys ) is most accurate in these settings is not known. In this real-world study of 9404 concurrent measurements of creatinine, cystatin C, and iohexol clearance, all three equations performed similarly when eGFR cr and eGFR cys were similar (45% of cases). However, with large discordances (55% of cases), eGFR cr-cys was much more accurate than either alone. These findings were consistent among individuals with cardiovascular disease, heart failure, diabetes mellitus, liver disease, and cancer who have been underrepresented in research cohorts. Thus, when eGFR cr and eGFR cys are largely discordant in clinical practice, eGFR cr-cys is more accurate than eGFR cr or eGFR cys . BACKGROUND: Cystatin C is recommended as a confirmatory test to eGFR when more precise estimates are needed for clinical decision making. Although eGFR on the basis of both creatinine and cystatin (eGFR cr-cys ) is the most accurate estimate in research studies, it is uncertain whether this is true in real-world settings, particularly when there are large discordances between eGFR based on creatinine (eGFR cr ) and that based on cystatin C (eGFR cys ). METHODS: We included 6185 adults referred for measured GFR (mGFR) using plasma clearance of iohexol in Stockholm, Sweden, who had 9404 concurrent measurements of creatinine, cystatin C, and iohexol clearance. The performance of eGFR cr , eGFR cys , and eGFR cr-cys was assessed against mGFR with median bias, P30 , and correct classification of GFR categories. We stratified analyses within three categories: eGFR cys at least 20% lower than eGFR cr (eGFR cys eGFR cr ). RESULTS: eGFR cr and eGFR cys were similar in 4226 (45%) samples, and among these samples all three estimating equations performed similarly. By contrast, eGFR cr-cys was much more accurate in cases of discordance. For example, when eGFR cys eGFR cr (8% of samples), the median biases were -4.5, 8.4, and 1.4 ml/min per 1.73m 2 . The findings were consistent among individuals with cardiovascular disease, heart failure, diabetes mellitus, liver disease, and cancer. CONCLUSIONS: When eGFR cr and eGFR cys are highly discordant in clinical practice, eGFR cr-cys is more accurate than either eGFR cr or eGFR cys .

Alterations in the Circulating Proteome Associated with Albuminuria.

SIGNIFICANCE STATEMENT: We describe circulating proteins associated with albuminuria in a population of African American Study of Kidney Disease and Hypertension with CKD (AASK) using the largest proteomic platform to date: nearly 7000 circulating proteins, representing approximately 2000 new targets. Findings were replicated in a subset of a general population cohort with kidney disease (ARIC) and a population with CKD Chronic Renal Insufficiency Cohort (CRIC). In cross-sectional analysis, 104 proteins were significantly associated with albuminuria in the Black group, of which 67 of 77 available proteins were replicated in ARIC and 68 of 71 available proteins in CRIC. LMAN2, TNFSFR1B, and members of the ephrin superfamily had the strongest associations. Pathway analysis also demonstrated enrichment of ephrin family proteins. BACKGROUND: Proteomic techniques have facilitated understanding of pathways that mediate decline in GFR. Albuminuria is a key component of CKD diagnosis, staging, and prognosis but has been less studied than GFR. We sought to investigate circulating proteins associated with higher albuminuria. METHODS: We evaluated the cross-sectional associations of the blood proteome with albuminuria and longitudinally with doubling of albuminuria in the African American Study of Kidney Disease and Hypertension (AASK; 38% female; mean GFR 46; median urine protein-to-creatinine ratio 81 mg/g; n =703) and replicated in two external cohorts: a subset of the Atherosclerosis Risk in Communities (ARIC) study with CKD and the Chronic Renal Insufficiency Cohort (CRIC). RESULTS: In cross-sectional analysis, 104 proteins were significantly associated with albuminuria in AASK, of which 67 of 77 available proteins were replicated in ARIC and 68 of 71 available proteins in CRIC. Proteins with the strongest associations included LMAN2, TNFSFR1B, and members of the ephrin superfamily. Pathway analysis also demonstrated enrichment of ephrin family proteins. Five proteins were significantly associated with worsening albuminuria in AASK, including LMAN2 and EFNA4, which were replicated in ARIC and CRIC. CONCLUSIONS: Among individuals with CKD, large-scale proteomic analysis identified known and novel proteins associated with albuminuria and suggested a role for ephrin signaling in albuminuria progression.

Testican-2 Is Associated with Reduced Risk of Incident ESKD.

BACKGROUND: Testican-2 was recently identified as a podocyte-derived protein that is released into circulation by the kidneys and is positively correlated with eGFR and eGFR slope. However, whether higher testican-2 levels are associated with lower risk of ESKD is unknown. METHODS: Aptamer-based proteomics assessed blood testican-2 levels among participants in the African American Study of Kidney Disease and Hypertension (AASK, n =703), the Chronic Renal Insufficiency Cohort (CRIC) study ( n =3196), and the Atherosclerosis Risk in Communities (ARIC) study ( n =4378). We compared baseline characteristics by testican-2 tertile and used Cox proportional hazards models to study the association of testican-2 with incident ESKD. RESULTS: Higher testican-2 levels were associated with higher measured GFR (mGFR) in AASK, higher eGFR in the CRIC and ARIC studies, and lower albuminuria in all cohorts. Baseline testican-2 levels were significantly associated with incident ESKD in Cox proportional hazards models adjusted for age, sex, and race (model 1) and model 1+mGFR or eGFR+comorbidities (model 2). In model 3 (model 2+proteinuria), the associations between testican-2 (per SD increase) and incident ESKD were AASK (hazard ratio [HR]=0.84 [0.72 to 0.98], P =0.023), CRIC (HR=0.95 [0.89 to 1.02], P =0.14), ARIC (HR=0.54 [0.36 to 0.83], P =0.0044), and meta-analysis (HR=0.92 [0.86 to 0.98], P =0.0073). CONCLUSIONS: Across three cohorts spanning >8000 individuals, testican-2 is associated with kidney health and prognosis, with higher levels associated with reduced risk of ESKD.

Unbiased Human Kidney Tissue Proteomics Identifies Matrix Metalloproteinase 7 as a Kidney Disease Biomarker.

SIGNIFICANCE STATEMENT: Although gene expression changes have been characterized in human diabetic kidney disease (DKD), unbiased tissue proteomics information for this condition is lacking. The authors conducted an unbiased aptamer-based proteomic analysis of samples from patients with DKD and healthy controls, identifying proteins with levels that associate with kidney function (eGFR) or fibrosis, after adjusting for key covariates. Overall, tissue gene expression only modestly correlated with tissue protein levels. Kidney protein and RNA levels of matrix metalloproteinase 7 (MMP7) strongly correlated with fibrosis and with eGFR. Single-cell RNA sequencing indicated that kidney tubule cells are an important source of MMP7. Furthermore, plasma MMP7 levels predicted future kidney function decline. These findings identify kidney tissue MMP7 as a biomarker of fibrosis and blood MMP7 as a biomarker for future kidney function decline. BACKGROUND: Diabetic kidney disease (DKD) is responsible for close to half of all ESKD cases. Although unbiased gene expression changes have been extensively characterized in human kidney tissue samples, unbiased protein-level information is not available. METHODS: We collected human kidney samples from 23 individuals with DKD and ten healthy controls, gathered associated clinical and demographics information, and implemented histologic analysis. We performed unbiased proteomics using the SomaScan platform and quantified the level of 1305 proteins and analyzed gene expression levels by bulk RNA and single-cell RNA sequencing (scRNA-seq). We validated protein levels in a separate cohort of kidney tissue samples as well as in 11,030 blood samples. RESULTS: Globally, human kidney transcript and protein levels showed only modest correlation. Our analysis identified 14 proteins with kidney tissue levels that correlated with eGFR and found that the levels of 152 proteins correlated with interstitial fibrosis. Of the identified proteins, matrix metalloprotease 7 (MMP7) showed the strongest association with both fibrosis and eGFR. The correlation between tissue MMP7 protein expression and kidney function was validated in external datasets. The levels of MMP7 RNA correlated with fibrosis in the primary and validation datasets. Findings from scRNA-seq pointed to proximal tubules, connecting tubules, and principal cells as likely cellular sources of increased tissue MMP7 expression. Furthermore, plasma MMP7 levels correlated not only with kidney function but also associated with prospective kidney function decline. CONCLUSIONS: Our findings, which underscore the value of human kidney tissue proteomics analysis, identify kidney tissue MMP7 as a diagnostic marker of kidney fibrosis and blood MMP7 as a biomarker for future kidney function decline.

The Kidney Failure Risk Equation: Evaluation of Novel Input Variables including eGFR Estimated Using the CKD-EPI 2021 Equation in 59 Cohorts.

SIGNIFICANCE STATEMENT: The kidney failure risk equation (KFRE) uses age, sex, GFR, and urine albumin-to-creatinine ratio (ACR) to predict 2- and 5-year risk of kidney failure in populations with eGFR <60 ml/min per 1.73 m 2 . However, the CKD-EPI 2021 creatinine equation for eGFR is now recommended for use but has not been fully tested in the context of KFRE. In 59 cohorts comprising 312,424 patients with CKD, the authors assessed the predictive performance and calibration associated with the use of the CKD-EPI 2021 equation and whether additional variables and accounting for the competing risk of death improves the KFRE's performance. The KFRE generally performed well using the CKD-EPI 2021 eGFR in populations with eGFR <45 ml/min per 1.73 m 2 and was not improved by adding the 2-year prior eGFR slope and cardiovascular comorbidities. BACKGROUND: The kidney failure risk equation (KFRE) uses age, sex, GFR, and urine albumin-to-creatinine ratio (ACR) to predict kidney failure risk in people with GFR <60 ml/min per 1.73 m 2 . METHODS: Using 59 cohorts with 312,424 patients with CKD, we tested several modifications to the KFRE for their potential to improve the KFRE: using the CKD-EPI 2021 creatinine equation for eGFR, substituting 1-year average ACR for single-measure ACR and 1-year average eGFR in participants with high eGFR variability, and adding 2-year prior eGFR slope and cardiovascular comorbidities. We also assessed calibration of the KFRE in subgroups of eGFR and age before and after accounting for the competing risk of death. RESULTS: The KFRE remained accurate and well calibrated overall using the CKD-EPI 2021 eGFR equation. The other modifications did not improve KFRE performance. In subgroups of eGFR 45-59 ml/min per 1.73 m 2 and in older adults using the 5-year time horizon, the KFRE demonstrated systematic underprediction and overprediction, respectively. We developed and tested a new model with a spline term in eGFR and incorporating the competing risk of mortality, resulting in more accurate calibration in those specific subgroups but not overall. CONCLUSIONS: The original KFRE is generally accurate for eGFR <45 ml/min per 1.73 m 2 when using the CKD-EPI 2021 equation. Incorporating competing risk methodology and splines for eGFR may improve calibration in low-risk settings with longer time horizons. Including historical averages, eGFR slopes, or a competing risk design did not meaningfully alter KFRE performance in most circumstances.