Faculty Bibliography

BACKGROUND AND OBJECTIVES/OBJECTIVE:Hemostatic factors have been associated with kidney function decline, and evidence suggests stronger effects among African Americans. The presence of APOL1 renal risk variants, common in African Americans, might partly underlie this risk difference. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS/METHODS:A total of 13,337 participants in the Atherosclerosis Risk in Communities study were followed from 1987-1989 until 2010. Participants were categorized into three groups by ancestry and APOL1 risk status: European Americans (n=10,206), African Americans with zero or one APOL1 risk allele (n=2,733), and African Americans with two APOL1 risk alleles (n=398). ESRD events were ascertained through linkage to the US Renal Data System. Cox regression was used to estimate the risk for ESRD associated with hemostatic factors (factor VIIc, factor VIIIc, fibrinogen, von Willebrand factor, protein C, and antithrombin III). RESULTS:There were 232 cases of ESRD over 21.5 years (European Americans, 119; African Americans with zero or one APOL1 risk allele, 94; African Americans with two APOL1 risk alleles, 19). In unadjusted and adjusted analysis of the overall population, higher levels of all hemostatic factors, except antithrombin III, were significantly associated with ESRD (all P<0.05). Factor VIIc had the strongest association (per one interquartile range; adjusted hazard ratio, 1.46; 95% confidence interval, 1.21 to 1.76). With the exception of fibrinogen, the risk associated with each hemostatic factor was stronger in African Americans with two APOL1 risk alleles compared with the other two groups. Statistically significant interactions were seen for factor VIIIc and protein C (interaction between those with two APOL1 risk allele and the other two groups: P<0.02 for factor VIIIc and <0.04 for protein C). CONCLUSIONS:Higher levels of factor VIIc, VIIIc, fibrinogen, von Willebrand factor, and protein C were associated with ESRD risk, with a significantly stronger association of factor VIIIc and protein C in African Americans with two APOL1 risk alleles.

BACKGROUND AND OBJECTIVES/OBJECTIVE:Liver fatty acid binding protein (L-FABP), kidney injury molecule 1 (KIM-1), N-acetyl-β-d-glucosaminidase (NAG), and neutrophil gelatinase-associated lipocalin (NGAL) are urinary markers of tubular injury that may also be markers of chronic kidney damage. We evaluated the association of these markers with incident ESRD in a community-based sample from the Atherosclerosis Risk in Communities Study. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS/METHODS:This was a matched case-control study of 135 patients with ESRD and 186 controls who were matched on sex, race, kidney function, and diabetes status at baseline (Atherosclerosis Risk in Communities Study visit 4, 1996-1998). Urinary KIM-1 indexed to creatinine (Cr), NAG/Cr, NGAL/Cr, and L-FABP/Cr were measured in stored spot urine samples from the baseline examination. Associations of KIM-1/Cr, NAG/Cr, and NGAL/Cr with patients with incident ESRD through 2008 were modeled continuously and categorically (quartiles) using conditional logistic regression. L-FABP/Cr was modeled only categorically because of a large number of measurements below the lower limit of detection for the assay (2.4 ng/ml). RESULTS:No significant associations were observed for NAG/Cr, NGAL/Cr, or L-FABP/Cr with ESRD. Those in the highest category for KIM-1/Cr had a higher risk of ESRD compared with those with undetectable biomarker levels (reference group) in unadjusted models (odds ratio, 2.24; 95% confidence interval, 1.97 to 4.69; P=0.03) or adjustment for age (odds ratio, 2.23; 95% confidence interval, 1.06 to 4.67; P=0.03). This association was attenuated with additional adjustment for baseline kidney function (odds ratio, 2.02; 95% confidence interval, 0.95 to 4.31; P=0.07 after additional adjustment for eGFR and natural log of the urinary albumin-to-creatinine ratio). No association between KIM-1/Cr and ESRD was found when KIM-1/Cr was analyzed as a continuous variable. CONCLUSIONS:Elevated urinary KIM-1/Cr may be associated with a higher risk of incident ESRD, but it does not add to risk prediction after accounting for traditional markers of kidney function in this population.

BACKGROUND AND OBJECTIVES/OBJECTIVE:Kidney disease progression, assessed by change in eGFR on the basis of creatinine, is an independent risk factor for cardiovascular disease and death. This study aimed to evaluate whether changes in multiple filtration markers, individually and combined, were associated with cardiovascular disease and death. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS/METHODS:Creatinine, cystatin C, and β2-microglobulin were measured among 9716 Atherosclerosis Risk in Communities Study participants in 1990-1992 and 1996-1998. Percentage change in three filtration markers (eGFR on the basis of creatinine, eGFR on the basis of cystatin C, and 1/β2-microglobulin) individually and the average of percentage change across all three filtration markers were calculated. Cardiovascular events and deaths were ascertained from 1996 to 2011. Cox regression models were adjusted for established risk factors for cardiovascular disease and mortality and first measurement of eGFR on the basis of creatinine. RESULTS:During a median follow-up of 14 years, there were 1922 cardiovascular events and 2285 deaths from any cause. Decline of >30% in each filtration marker was significantly associated with higher risk of mortality compared with stable kidney function (-9.9% to +9.9% change in the filtration marker) with hazard ratios (95% confidence intervals) of 1.91 (1.67 to 2.18) for eGFR on the basis of creatinine, 2.29 (1.99 to 2.63) for eGFR on the basis of cystatin C, and 2.48 (2.15 to 2.86) for 1/β2-microglobulin, with similar associations for cardiovascular disease. An average decline of >30% across the three markers was strongly associated with higher risk of all-cause mortality (hazard ratio, 2.82; 95% confidence interval, 2.42 to 3.29). CONCLUSIONS:Kidney disease progression was assessed using >30% decline in eGFR on the basis of creatinine, eGFR on the basis of cystatin C, and 1/β2-microglobulin and average decline of >30% across the three filtration markers is strongly associated with risk of cardiovascular disease and death.

BACKGROUND:Linkage to the US Renal Data System (USRDS) registry commonly is used to identify end-stage renal disease (ESRD) cases, or kidney failure treated with dialysis or transplantation, but it underestimates the total burden of kidney failure. This study validates a kidney failure definition that includes both kidney failure treated and not treated by dialysis or transplantation. It compares kidney failure risk factors and outcomes using this broader definition with USRDS-identified ESRD risk factors and outcomes. STUDY DESIGN/METHODS:Diagnostic test study with stratified random sampling of hospitalizations for chart review. SETTING & PARTICIPANTS/METHODS:Atherosclerosis Risk in Communities Study (n=11,530; chart review, n=546). INDEX TEST/METHODS:USRDS-identified ESRD; treated or untreated kidney failure defined by USRDS-identified ESRD or International Classification of Diseases, Ninth or Tenth Revision, Clinical Modification (ICD-9-CM/ICD-10-CM) code for hospitalization or death. REFERENCE TEST/METHODS:For ESRD, determination of permanent dialysis therapy or transplantation; for kidney failure, determination of permanent dialysis therapy, transplantation, or estimated glomerular filtration rate < 15 mL/min/1.73 m(2). RESULTS:During 13 years' median follow-up, 508 kidney failure cases were identified, including 173 (34.1%) from the USRDS registry. ESRD and kidney failure incidence were 1.23 and 3.66 cases per 1,000 person-years in the overall population and 1.35 and 6.59 cases per 1,000 person-years among participants older than 70 years, respectively. Other risk-factor associations were similar between ESRD and kidney failure, except diabetes and albuminuria, which were stronger for ESRD. Survivals at 1 and 5 years were 74.0% and 24.0% for ESRD and 59.8% and 31.6% for kidney failure, respectively. Sensitivity and specificity were 88.0% and 97.3% comparing the kidney failure ICD-9-CM/ICD-10-CM code algorithm to chart review; for USRDS-identified ESRD, sensitivity and specificity were 94.9% and 100.0%. LIMITATIONS/CONCLUSIONS:Some medical charts were incomplete. CONCLUSIONS:A kidney failure definition including treated and untreated disease identifies more cases than linkage to the USRDS registry alone, particularly among older adults. Future studies might consider reporting both USRDS-identified ESRD and a more inclusive kidney failure definition.

BACKGROUND:Chronic kidney disease progression is a risk factor for end-stage renal disease (ESRD). A 57% decline in creatinine-based estimated glomerular filtration rate (eGFRcr) is an established surrogate outcome for ESRD in clinical trials, and a 30% decrease recently has been proposed as a surrogate end point. However, it is unclear whether change in novel filtration marker levels provides additional information for ESRD risk to change in eGFRcr. STUDY DESIGN/METHODS:Cohort study. SETTING & PARTICIPANTS/METHODS:Atherosclerosis Risk in Communities (ARIC) Study participants from 4 US communities. PREDICTORS/METHODS:Percent change in levels of filtration markers (eGFRcr, cystatin C-based eGFR [eGFRcys], the inverse of β2-microglobulin concentration [1/B2M]) over a 6-year period. OUTCOME/RESULTS:Incident ESRD. MEASUREMENTS/METHODS:Cox proportional hazards regression with adjustment for demographics, kidney disease risk factors, and first measurement of eGFRcr. RESULTS:During a median follow-up of 13 years, there were 142 incident ESRD cases. In adjusted analysis, declines > 30% in eGFRcr, eGFRcys, and 1/B2M were associated significantly with ESRD compared with stable concentrations of filtration markers (HRs of 19.96 [95% CI, 11.73-33.96], 16.67 [95% CI, 10.27-27.06], and 22.53 [95% CI, 13.20-38.43], respectively). Using the average of declines in the 3 markers, >30% decline conferred higher ESRD risk than that for eGFRcr alone (HR, 31.97 [95% CI, 19.40-52.70; P=0.03] vs eGFRcr). LIMITATIONS/CONCLUSIONS:Measurement error could influence estimation of change in filtration marker levels. CONCLUSIONS:A >30% decline in kidney function assessed using novel filtration markers is associated strongly with ESRD, suggesting the potential utility of measuring change in cystatin C and B2M levels in settings in which improved outcome ascertainment is needed, such as clinical trials.

BACKGROUND:Epidemiologic data for cardiac abnormality predating decreased kidney function are sparse. We investigated the associations of high-sensitivity cardiac troponin T (hs-cTnT) and N-terminal pro-brain natriuretic peptide (NT-proBNP) with end-stage renal disease (ESRD) risk in a community-based cohort. STUDY DESIGN/METHODS:A prospective cohort study. SETTING & PARTICIPANTS/METHODS:10,749 white and black participants at the fourth visit (1996-1998) of the Atherosclerosis Risk in Communities (ARIC) Study with follow-up through 2010. PREDICTOR/METHODS:hs-cTnT (3, 6, 9, and 14ng/L) and NT-proBNP (41.6, 81.0, 142.5, and 272.5pg/mL) levels were divided into 5 categories at the same percentiles (32th, 57th, 77th, and 91th; corresponding to ordinary thresholds of hs-cTnT), with the lowest category as a reference. OUTCOMES/RESULTS:Incident ESRD defined as initiation of dialysis therapy, transplantation, or death due to kidney disease. MEASUREMENTS/METHODS:Relative risk and risk prediction of ESRD according to hs-cTnT and NT-proBNP levels based on Cox proportional hazards models. RESULTS:During a median follow-up of 13.1 years, 235 participants developed ESRD (1.8 cases/1,000 person-years). hs-cTnT and NT-proBNP levels were associated with ESRD risk independently of each other and of potential confounders, including kidney function and albuminuria (adjusted HRs for highest category, 4.43 [95% CI, 2.43-8.09] and 2.28 [95% CI, 1.44-3.60], respectively). For hs-cTnT level, the association was significant even at the third category (HR for 6-8ng/L of hs-cTnT, 2.74 [95% CI, 1.54-4.88]). Their associations were largely consistent even among persons without decreased kidney function or history of cardiovascular disease. hs-cTnT and NT-proBNP levels both significantly improved ESRD prediction (C statistic differences of 0.0084 [95% CI, 0.0005-0.0164] and 0.0045 [95% CI, 0.0004-0.0087], respectively, from 0.884 with conventional risk factors). LIMITATIONS/CONCLUSIONS:Relatively small number of ESRD cases and single measurement of hs-cTnT and NT-proBNP. CONCLUSIONS:hs-cTnT and NT-proBNP levels independently predicted ESRD risk in the general population, with more evident results for hs-cTnT. These results suggest the involvement of cardiac abnormality, particularly cardiac injury, in the progression of reduced kidney function and/or may reflect the useful property of hs-cTnT as an end-organ damage marker.

BACKGROUND:Acute kidney injury (AKI) is a serious global public health problem. We aimed to quantify the risk of AKI associated with estimated glomerular filtration rate (eGFR), albuminuria (albumin-creatinine ratio [ACR]), age, sex, and race (African American and white). STUDY DESIGN/METHODS:Collaborative meta-analysis. SETTING & POPULATION/METHODS:8 general-population cohorts (1,285,049 participants) and 5 chronic kidney disease (CKD) cohorts (79,519 participants). SELECTION CRITERIA FOR STUDIES/METHODS:Available eGFR, ACR, and 50 or more AKI events. PREDICTORS/METHODS:Age, sex, race, eGFR, urine ACR, and interactions. OUTCOME/RESULTS:Hospitalized with or for AKI, using Cox proportional hazards models to estimate HRs of AKI and random-effects meta-analysis to pool results. RESULTS:16,480 (1.3%) general-population cohort participants had AKI over a mean follow-up of 4 years; 2,087 (2.6%) CKD participants had AKI over a mean follow-up of 1 year. Lower eGFR and higher ACR were strongly associated with AKI. Compared with eGFR of 80mL/min/1.73m(2), the adjusted HR of AKI at eGFR of 45mL/min/1.73m(2) was 3.35 (95% CI, 2.75-4.07). Compared with ACR of 5mg/g, the risk of AKI at ACR of 300mg/g was 2.73 (95% CI, 2.18-3.43). Older age was associated with higher risk of AKI, but this effect was attenuated with lower eGFR or higher ACR. Male sex was associated with higher risk of AKI, with a slight attenuation in lower eGFR but not in higher ACR. African Americans had higher AKI risk at higher levels of eGFR and most levels of ACR. LIMITATIONS/CONCLUSIONS:Only 2 general-population cohorts could contribute to analyses by race; AKI identified by diagnostic code. CONCLUSIONS:Reduced eGFR and increased ACR are consistent strong risk factors for AKI, whereas associations of AKI with age, sex, and race may be weaker in more advanced stages of CKD.

BACKGROUND:Equivalence of laboratory tests over time is important for longitudinal studies. Even a small systematic difference (bias) can result in substantial misclassification. METHODS:We selected 200 Atherosclerosis Risk in Communities Study participants attending all 5 study visits over 25 years. Eight analytes were remeasured in 2011-2013 from stored blood samples from multiple visits: creatinine, uric acid, glucose, total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, and high-sensitivity C-reactive protein. Original values were recalibrated to remeasured values with Deming regression. Differences >10% were considered to reflect substantial bias, and correction equations were applied to affected analytes in the total study population. We examined trends in chronic kidney disease (CKD) pre- and postrecalibration. RESULTS:Repeat measures were highly correlated with original values [Pearson r > 0.85 after removing outliers (median 4.5% of paired measurements)], but 2 of 8 analytes (creatinine and uric acid) had differences >10%. Original values of creatinine and uric acid were recalibrated to current values with correction equations. CKD prevalence differed substantially after recalibration of creatinine (visits 1, 2, 4, and 5 prerecalibration: 21.7%, 36.1%, 3.5%, and 29.4%, respectively; postrecalibration: 1.3%, 2.2%, 6.4%, and 29.4%). For HDL cholesterol, the current direct enzymatic method differed substantially from magnesium dextran precipitation used during visits 1-4. CONCLUSIONS:Analytes remeasured in samples stored for approximately 25 years were highly correlated with original values, but 2 of the 8 analytes showed substantial bias at multiple visits. Laboratory recalibration improved reproducibility of test results across visits and resulted in substantial differences in CKD prevalence. We demonstrate the importance of consistent recalibration of laboratory assays in a cohort study.

BACKGROUND:Advanced glycation end products and their cell-bound receptors are thought to mediate the adverse effects of vascular disease through oxidative stress, inflammation and endothelial dysfunction. We examined the association between the soluble form of receptor for advanced glycation end products (sRAGE) and kidney disease. METHODS:In this case-cohort study nested within the Atherosclerosis Risk in Communities (ARIC) study, baseline sRAGE levels were measured in a cohort random sample of participants without kidney disease (n= 1218), and among participants who developed incident chronic kidney disease (CKD) [estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2) and ≥25% eGFR decline, n = 151] and end-stage renal disease (ESRD) [entry in the US Renal Data System (USRDS) registry, n = 152]. RESULTS:Baseline sRAGE levels were inversely related to baseline eGFR (r = -0.13). After adjusting for age, sex and race, one interquartile range higher log10-transformed sRAGE was associated with development of CKD [odds ratio: 1.39; 95% confidence interval (95% CI) 1.06-1.83; P = 0.02] and ESRD (hazard ratio: 1.97; 95% CI 1.47-2.64; P < 0.001). These associations were not significant after eGFR adjustment. CONCLUSIONS:High sRAGE levels are associated with incident CKD and ESRD risk, but not after adjustment for kidney function at baseline. Future studies are needed to investigate specific mechanisms underlying the association of sRAGE with kidney disease risk.

Fibroblast growth factor-23 is a bone-derived hormone that increases urinary phosphate excretion and inhibits hydroxylation of 25-hydroxyvitamin D. Recent studies suggest that fibroblast growth factor-23 may be an early biomarker of CKD progression. However, its role in kidney function decline in the general population is unknown. We assessed the relationship between baseline (1990-1992) serum levels of intact fibroblast growth factor-23 and incident ESRD in 13,448 Atherosclerosis Risk in Communities study participants (56.1% women, 74.7% white) followed until December 31, 2010. At baseline, the mean age of participants was 56.9 years and the mean eGFR was 97 ml/min per 1.73 m(2). During a median follow-up of 19 years, 267 participants (2.0%) developed ESRD. After adjustment for demographic characteristics, baseline eGFR, traditional CKD risk factors, and markers of mineral metabolism, the highest fibroblast growth factor-23 quintile (>54.6 pg/ml) compared with the lowest quintile (<32.0 pg/ml) was associated with risk of developing ESRD (hazard ratio, 2.10; 95% confidence interval, 1.31 to 3.36; trend P<0.001). In a large, community-based study comprising a broad range of kidney function, higher baseline fibroblast growth factor-23 levels were associated with increased risk of incident ESRD independent of the baseline level of kidney function and a number of other risk factors.