Risk of incident ESRD: a comprehensive look at cardiovascular risk factors and 17 years of follow-up in the Atherosclerosis Risk in Communities (ARIC) Study

Advanced chronic kidney disease, end-stage renal disease and renal death among HIV-positive individuals in Europe

OBJECTIVES

Knowledge about advanced chronic kidney disease (CKD) and end-stage renal disease (ESRD) in HIV-positive persons is limited. The aim of this study was to investigate incidence, predictors and outcomes for advanced CKD/ESRD and renal death.

METHODS

Advanced CKD was defined as confirmed (two consecutive measurements ≥ 3 months apart) estimated glomerular filtration rate (eGFR) ≤ 30 mL/min/1.73 m(2) using Cockcroft-Gault, and ESRD as haemodialysis or peritoneal dialysis for ≥ 1 month or renal transplant. Renal death was death with renal disease as the underlying cause, using Coding Causes of Death in HIV (CoDe) methodology. Follow-up was from 1 January 2004 until last eGFR measurement, advanced CKD, ESRD or renal death, whichever occurred first. Poisson regression was used to identify predictors.

RESULTS

Of 9044 individuals included in the study, 58 (0.64%) experienced advanced CKD/ESRD/renal death [incidence rate 1.32/1000 person-years of follow-up (PYFU); 95% confidence interval (CI) 0.98-1.66]; 52% of those who experienced the endpoint had a baseline eGFR ≤ 60 mL/min/1.73 m(2) compared with 3% of those who did not. Using Kaplan-Meier methods, at 6 years from baseline, 0.83% (95% CI 0.59-1.07%) were estimated to have experienced the endpoint overall and 11.26% (95% CI 6.75-15.78%) among those with baseline eGFR ≤ 60 mL/min/1.73 m(2) . Independent predictors of the endpoint included any cardiovascular event [incidence rate ratio (IRR) 2.16; 95% CI 1.24-3.77], lower eGFR (IRR 0.64 per 5 mL/min/1.73 m(2) ; 95% CI 0.59-0.70) and lower CD4 count (IRR 0.77 per doubling; 95% CI 0.62-0.95). One year after experiencing advanced CKD or ESRD, an estimated 19.21% (95% CI 7.84-30.58%) of patients had died, mostly from extra-renal causes.

CONCLUSIONS

The incidence of advanced CKD/ESRD/renal death was low and predictors included traditional renal risk factors, HIV-related factors and pre-existing renal impairment. The prognosis following advanced CKD/ESRD was poor. Larger studies should address possible contributions of specific antiretrovirals.

Genome-wide association study identified the human leukocyte antigen region as a novel locus for plasma beta-2 microglobulin

Beta-2 microglobulin (B2M) is a component of the major histocompatibility complex (MHC) class I molecule and has been studied as a biomarker of kidney function, cardiovascular diseases and mortality. Little is known about the genes influencing its levels directly or through glomerular filtration rate (GFR). We conducted a genome-wide association study of plasma B2M levels in 6738 European Americans from the Atherosclerosis Risk in Communities study to identify novel loci for B2M and assessed its association with known estimated GFR (eGFR) loci. We identified 2 genome-wide significant loci. One was in the human leukocyte antigen (HLA) region on chromosome 6 (lowest p value = 1.8 × 10(-23) for rs9264638). At this locus, 6 index SNPs accounted for 3.2 % of log(B2M) variance, and their association with B2M could largely be explained by imputed classical alleles of the MHC class I genes: HLA-A, HLA-B, or HLA-C. The index SNPs at this locus were not associated with eGFR based on serum creatinine (eGFRcr). The other locus of B2M was on chromosome 12 (rs3184504 at SH2B3, beta = 0.02, p value = 3.1 × 10(-8)), which was previously implicated as an eGFR locus. In conclusion, although B2M is known to be a component of MHC class I molecule, the association between HLA class I alleles and plasma B2M levels in a community-based population is novel. The identification of the two novel loci for B2M extends our understanding of its metabolism and informs its use as a kidney filtration biomarker.

Genome-wide association study identified the human leukocyte antigen region as a novel locus for plasma beta-2 microglobulin

Beta-2 microglobulin (B2M) is a component of the major histocompatibility complex (MHC) class I molecule and has been studied as a biomarker of kidney function, cardiovascular diseases and mortality. Little is known about the genes influencing its levels directly or through glomerular filtration rate (GFR). We conducted a genome-wide association study of plasma B2M levels in 6738 European Americans from the Atherosclerosis Risk in Communities study to identify novel loci for B2M and assessed its association with known estimated GFR (eGFR) loci. We identified 2 genome-wide significant loci. One was in the human leukocyte antigen (HLA) region on chromosome 6 (lowest p value = 1.8 × 10(-23) for rs9264638). At this locus, 6 index SNPs accounted for 3.2 % of log(B2M) variance, and their association with B2M could largely be explained by imputed classical alleles of the MHC class I genes: HLA-A, HLA-B, or HLA-C. The index SNPs at this locus were not associated with eGFR based on serum creatinine (eGFRcr). The other locus of B2M was on chromosome 12 (rs3184504 at SH2B3, beta = 0.02, p value = 3.1 × 10(-8)), which was previously implicated as an eGFR locus. In conclusion, although B2M is known to be a component of MHC class I molecule, the association between HLA class I alleles and plasma B2M levels in a community-based population is novel. The identification of the two novel loci for B2M extends our understanding of its metabolism and informs its use as a kidney filtration biomarker.

Study design of DIACORE (DIAbetes COhoRtE) - a cohort study of patients with diabetes mellitus type 2

Background

Diabetes mellitus type 2 (DM2) is highly associated with increased risk for chronic kidney disease (CKD), end stage renal disease (ESRD) and cardiovascular morbidity. Epidemiological and genetic studies generate hypotheses for innovative strategies in DM2 management by unravelling novel mechanisms of diabetes complications, which is essential for future intervention trials. We have thus initiated the DIAbetes COhoRtE study (DIACORE).

Methods

DIACORE is a prospective cohort study aiming to recruit 6000 patients of self-reported Caucasian ethnicity with prevalent DM2 for at least 10 years of follow-up. Study visits are performed in University-based recruiting clinics in Germany using standard operating procedures. All prevalent DM2 patients in outpatient clinics surrounding the recruiting centers are invited to participate. At baseline and at each 2-year follow-up examination, patients are subjected to a core phenotyping protocol. This includes a standardized online questionnaire and physical examination to determine incident micro- and macrovascular DM2 complications, malignancy and hospitalization, with a primary focus on renal events. Confirmatory outcome information is requested from patient records. Blood samples are obtained for a centrally analyzed standard laboratory panel and for biobanking of aliquots of serum, plasma, urine, mRNA and DNA for future scientific use. A subset of the cohort is subjected to extended phenotyping, e.g. sleep apnea screening, skin autofluorescence measurement, non-mydriatic retinal photography and non-invasive determination of arterial stiffness.

Discussion

DIACORE will enable the prospective evaluation of factors involved in DM2 complication pathogenesis using high-throughput technologies in biosamples and genetic epidemiological studies.

Association of Obesity and Kidney Function Decline among Non-Diabetic Adults with eGFR > 60 ml/min/1.73m2: Results from the Multi-Ethnic Study of Atherosclerosis (MESA)

Background

Obesity is associated with higher end-stage renal disease incidence, but associations with earlier forms of kidney disease remain incompletely characterized.

Methods

We studied the association of body mass index (BMI), waist circumference (WC), and waist-to-hip ratio (WHR) with rapid kidney function decline and incident chronic kidney disease in 4573 non-diabetic adults with eGFR ≥ 60 ml/min/1.73m² at baseline from longitudinal Multi-Ethnic Study of Atherosclerosis cohort. Kidney function was estimated by creatinine and cystatin C. Multivariate analysis was adjusted for age, race, baseline eGFR, and hypertension.

Results

Mean age was 60 years old, BMI 28 kg/m², baseline eGFR_Cr 82 and eGFR_Cys 95 ml/min/1.73m². Over 5 years of follow up, 25% experienced rapid decline in renal function by eGFR_Cr and 22% by eGFR_Cys. Incident chronic kidney disease (CKD) developed in 3.3% by eGFR_Cys, 11% by eGFR_Cr, and 2.4% by both makers. Compared to persons with BMI < 25, overweight (BMI 25 – 30) persons had the lowest risk of rapid decline by eGFR_Cr (0.84, 0.71 – 0.99). In contrast, higher BMI categories were associated with stepwise higher odds of rapid decline by eGFR_Cys, but remained significant only when BMI ≥ 35 kg/m² (1.87, 1.41 – 2.48). Associations of BMI with incident CKD were insignificant after adjustment. Large WC and WHR were associated with increased risk of rapid decline only by eGFR_Cys, and of incident CKD only when defined by both filtration markers.

Conclusions

Obesity may be a risk factor for kidney function decline, but associations vary by filtration marker used.

Cardiovascular disease in chronic kidney disease: untying the Gordian knot

Chronic kidney disease (CKD) affects around 10-13% of the general population, with only a small proportion in end stage renal disease (ESRD), either on dialysis or awaiting renal transplantation. It is well documented that CKD patients have an extremely high risk of developing cardiovascular disease (CVD) compared with the general population, so much so that in the early stages of CKD patients are more likely to develop CVD than they are to progress to ESRD. Various pathophysiological pathways and explanations have been advanced and suggested to account for this, including endothelial dysfunction, dyslipidaemia, inflammation, left ventricular hypertrophy and cardiac autonomic dysfunction. In this review, we try to understand and further explore the link between CKD and CVD, as well as offering interventional advice where available, while exposing the current lack of RCT-based research and trial evidence in this area. We also suggest pragmatic Interim measures we could take while we wait for definitive RCTs.

Identification of a multistate continuous-time nonhomogeneous Markov chain model for patients with decreased renal function

OBJECTIVES

Markov chain models are frequently used to study the clinical course of chronic diseases. The aim of this article is to adopt statistical methods to describe the time dynamics of chronically ill patients when 2 kinds of data sets--fully and partially observable data are available.

MODEL

We propose a 6-state continuous-time Markov chain model for the progression of chronic kidney disease (CKD), where little is known about the transitions between the disease stages. States 1 to 3 of the model correspond to stages III to V of chronic kidney disease in the Kidney Disease Outcomes Quality Initiative (KDOQI) CKD classification. States 4 and 5 relate to dialysis and transplantation (renal replacement therapy), respectively. Death is the (absorbing) state 6.

METHODS AND DATA

The model can be investigated and identified using Kolmogorov's forward equations and the methods of survival analysis. Age dependency, covariates in the form of the Cox regression, and unobservable risks of transition (frailties) can be included in the model. We applied our model to a data set consisting of all 2097 patients from all renal centers in a region in North Rhine-Westphalia (Germany) in 2005-2010.

RESULTS

We compared transitions and relative risks to the few data published and found them to be reasonable. For example, patients with diabetes had a significantly higher risk for disease progression compared with patients without diabetes.

CONCLUSIONS

In summary, modeling may help to quantify disease progression and its predictors when only partially observable prospective data are available.

Association of race and body mass index with ESRD and mortality in CKD stages 3-4: results from the Kidney Early Evaluation Program (KEEP)

BACKGROUND

A recent cross-sectional analysis of Kidney Early Evaluation Program (KEEP) participants suggested that obesity is a heterogeneous disease state in African Americans and whites with chronic kidney disease (CKD).

STUDY DESIGN

In longitudinal analyses spanning 8 years of follow-up, we examined whether race and body mass index (BMI) influence end-stage renal disease (ESRD) and mortality rates in participants with CKD stages 3-4.

SETTING & PARTICIPANTS

KEEP participants were included in this analysis if they met the following criteria: (1) estimated glomerular filtration rate (eGFR) of 15-59 mL/min/1.73 m(2), (2) white or African American race, and (3) no previous dialysis or transplantation.

OUTCOMES & MEASUREMENTS

Survival analyses were performed for the outcomes of ESRD, death, and combined outcome of ESRD or death.

RESULTS

Of 14,631 participants with CKD stages 3-4, 28% were African American and 72% were white. African American participants had higher rates of obesity and hypertension, with a higher baseline mean eGFR, higher prevalence of albuminuria, and greater degree of anemia compared with whites. In multivariable models, African American race increased the risk of ESRD (HR, 1.66; 95% CI, 1.26-2.07), but not death (HR, 0.89; 95% CI, 0.76-1.03). In these models, male sex, hypertension, diabetes, lower baseline eGFR, and albuminuria were predictive of higher rates of ESRD; age, male sex, diabetes, lower baseline eGFR, and albuminuria were predictive of overall mortality. There was no significant interaction between race and BMI in the adjusted model for outcomes of ESRD (P = 0.7) or death (P = 0.3).

LIMITATIONS

Baseline values used in the analysis are from a cross-sectional data set. Dyslipidemia and secondary hyperparathyroidism were not accounted for in the analysis.

CONCLUSIONS

African American race was associated with a higher incidence of ESRD, but not mortality. Although obesity may be a heterogeneous disease state in African Americans and whites with CKD, there does not appear to be a significant interaction between race and BMI in progression to ESRD or death.

Incidence and predictors of end stage renal disease among low-income blacks and whites

We evaluated whether black race is associated with higher incidence of End Stage Renal Disease (ESRD) among a cohort of blacks and whites of similar, generally low socioeconomic status, and whether risk factor patterns differ among blacks and whites and explain the poorly understood racial disparity in ESRD. Incident diagnoses of ESRD among 79,943 black and white participants in the Southern Community Cohort Study (SCCS) were ascertained by linkage with the United States Renal Data System (USRDS) from 2002 through 2009. Person-years of follow up were calculated from date of entry into the SCCS until date of ESRD diagnosis, date of death, or September 1, 2009, whichever occurred first. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CI) for incident ESRD among black and white participants in relation to baseline characteristics. After 329,003 person-years of follow-up, 687 incident cases of ESRD were identified in the cohort. The age-adjusted ESRD incidence rate was 273 (per 100,000) among blacks, 3.5-fold higher than the rate of 78 among whites. Risk factors for ESRD included male sex (HR = 1.6; 95% CI 1.4–1.9), low income (HR = 1.5; 95% CI 1.2–1.8 for income below vs. above $15,000), smoking (HR = 1.2; 95% CI 1.02–1.4) and histories of diabetes (HRs increasing to 9.4 (95% CI 7.4–11.9) among those with ≥20 years diabetes duration) and hypertension (HR = 2.9; 95% CI 2.3–3.7). Patterns and magnitudes of association were virtually identical among blacks and whites. After adjustment for these risk factors, blacks continued to have a higher risk for ESRD (HR = 2.4; 95% CI = 1.9–3.0) relative to whites. The black-white disparity in risk of ESRD was attenuated but not eliminated after control for known risk factors in a closely socioeconomically matched cohort. Further research characterizing biomedical factors, including CKD progression, in ESRD occurrence in these two racial groups is needed.

Factors associated with chronic kidney disease progression in Australian nephrology practices

BACKGROUND/AIMS

Chronic kidney disease (CKD) is a major health issue worldwide. The aim of this study was to explore factors associated with CKD progression in Australian nephrology practices.

METHODS

This was a retrospective study utilising an electronic medical record (EMR), Audit4 (Software for Specialists, Australia). The baseline visit was defined as the first entry into the EMR. The primary outcome was the rate of change in estimated glomerular filtration rate (eGFR).

RESULTS

1,328 patients were included with a mean eGFR at baseline of 37.4 ± 0.7 ml/min/1.73 m(2), a mean follow-up of 17.7 months and a mean annual rate of change in eGFR of -0.84 ± 0.26 ml/min/1.73 m(2). Univariate analysis demonstrated that women, smokers, and patients prescribed erythropoiesis-stimulating agents (ESA) had a significantly more rapid decline in eGFR (p = 0.007, 0.033, and 0.003, respectively). On multivariate analysis: gender, age, prescription of ESA and phosphate binders, and baseline eGFR were significantly associated with CKD progression (p = 0.003, 0.004, <0.001, 0.029, and <0.001, respectively).

CONCLUSIONS

This study identifies potential factors associated with CKD progression in a population referred to nephrologists, but current data quality may result in bias. Implementation of changes in the format of data collection is required so that busy clinicians record essential information to enable this to become a more accurate and reliable research tool.

Diabetes and kidney transplantation: past, present, and future

Diabetes mellitus is the most common etiology for end stage renal disease (ESRD) worldwide and in the United States. The incidence of morbidity and mortality is higher in diabetic patients with ESRD due to increased cardiovascular events. Patients with type 2 diabetes who receive a renal allograft have a higher survival rate compared with patients who are maintained on chronic hemodialysis therapy, but there is scarcity of data on long-term graft outcomes. Most recently the development of new onset diabetes after transplantation (NODAT) poses a serious threat to patient and allograft survival. Pre-emptive transplantation and the use of living donors have improved overall survival. In addition, critical management of glucose, blood pressure, and cholesterol are some of the factors that can help minimize adverse outcomes in both patients with pre-existing diabetes and patients who develop NODAT. Future clinical trials are warranted to improve therapeutic medical management of these patients thus influencing graft attrition.

Novel markers of kidney function as predictors of ESRD, cardiovascular disease, and mortality in the general population

BACKGROUND

Cystatin C level predicts mortality more strongly than serum creatinine level. It is unknown whether this advantage extends to other outcomes, such as kidney failure, or whether other novel renal filtration markers share this advantage in predicting outcomes.

STUDY DESIGN

Observational cohort study.

SETTING & PARTICIPANTS

9,988 participants in the Atherosclerosis Risk in Communities (ARIC) Study, a population-based study in 4 US communities, followed for approximately 10 years.

PREDICTORS

Serum creatinine-based estimated glomerular filtration rate calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation (eGFR(CKD-EPI)) and cystatin C, β-trace protein (BTP), and β(2)-microglobulin (B2M) levels.

OUTCOMES

Mortality, coronary heart disease, heart failure, and kidney failure.

RESULTS

Higher cystatin C and B2M concentrations were associated more strongly with mortality (n = 1,425) than BTP level and all were associated more strongly than eGFR(CKD-EPI) (adjusted HR for the upper 6.7 percentile compared with the lowest quintile: 1.6 [95% CI, 1.3-1.9] for eGFR(CKD-EPI), 2.9 [95% CI, 2.3-3.6] for cystatin C level, 1.9 [95% CI, 1.5-2.4] for BTP level, and 3.0 [95% CI, 2.4-3.8] for B2M level). Similar patterns were observed for coronary heart disease (n = 1,279), heart failure (n = 803), and kidney failure (n = 130). The addition of cystatin C, BTP, and B2M levels to models including eGFR(CKD-EPI) and all covariates, including urinary albumin-creatinine ratio, significantly improved risk prediction for all outcomes (P < 0.001).

LIMITATIONS

No direct measurement of GFR.

CONCLUSIONS

B2M and, to a lesser extent, BTP levels share cystatin C's advantage over eGFR(CKD-EPI) in predicting outcomes, including kidney failure. These additional markers may be helpful in improving estimation of risk associated with decreased kidney function beyond current estimates based on eGFR(CKD-EPI).

Estimating individual glomerular volume in the human kidney: clinical perspectives

BACKGROUND

Measurement of individual glomerular volumes (IGV) has allowed the identification of drivers of glomerular hypertrophy in subjects without overt renal pathology. This study aims to highlight the relevance of IGV measurements with possible clinical implications and determine how many profiles must be measured in order to achieve stable size distribution estimates.

METHODS

We re-analysed 2250 IGV estimates obtained using the disector/Cavalieri method in 41 African and 34 Caucasian Americans. Pooled IGV analysis of mean and variance was conducted. Monte-Carlo (Jackknife) simulations determined the effect of the number of sampled glomeruli on mean IGV. Lin's concordance coefficient (R(C)), coefficient of variation (CV) and coefficient of error (CE) measured reliability.

RESULTS

IGV mean and variance increased with overweight and hypertensive status. Superficial glomeruli were significantly smaller than juxtamedullary glomeruli in all subjects (P < 0.01), by race (P < 0.05) and in obese individuals (P < 0.01). Subjects with multiple chronic kidney disease (CKD) comorbidities showed significant increases in IGV mean and variability. Overall, mean IGV was particularly reliable with nine or more sampled glomeruli (R(C) > 0.95, <5% difference in CV and CE). These observations were not affected by a reduced sample size and did not disrupt the inverse linear correlation between mean IGV and estimated total glomerular number.

CONCLUSIONS

Multiple comorbidities for CKD are associated with increased IGV mean and variance within subjects, including overweight, obesity and hypertension. Zonal selection and the number of sampled glomeruli do not represent drawbacks for future longitudinal biopsy-based studies of glomerular size and distribution.

Association of eGFR-Related Loci Identified by GWAS with Incident CKD and ESRD

Family studies suggest a genetic component to the etiology of chronic kidney disease (CKD) and end stage renal disease (ESRD). Previously, we identified 16 loci for eGFR in genome-wide association studies, but the associations of these single nucleotide polymorphisms (SNPs) for incident CKD or ESRD are unknown. We thus investigated the association of these loci with incident CKD in 26,308 individuals of European ancestry free of CKD at baseline drawn from eight population-based cohorts followed for a median of 7.2 years (including 2,122 incident CKD cases defined as eGFR <60ml/min/1.73m² at follow-up) and with ESRD in four case-control studies in subjects of European ancestry (3,775 cases, 4,577 controls). SNPs at 11 of the 16 loci (UMOD, PRKAG2, ANXA9, DAB2, SHROOM3, DACH1, STC1, SLC34A1, ALMS1/NAT8, UBE2Q2, and GCKR) were associated with incident CKD; p-values ranged from p = 4.1e-9 in UMOD to p = 0.03 in GCKR. After adjusting for baseline eGFR, six of these loci remained significantly associated with incident CKD (UMOD, PRKAG2, ANXA9, DAB2, DACH1, and STC1). SNPs in UMOD (OR = 0.92, p = 0.04) and GCKR (OR = 0.93, p = 0.03) were nominally associated with ESRD. In summary, the majority of eGFR-related loci are either associated or show a strong trend towards association with incident CKD, but have modest associations with ESRD in individuals of European descent. Additional work is required to characterize the association of genetic determinants of CKD and ESRD at different stages of disease progression.

Chronic kidney disease (CKD) affects about 6%–11% of the general population, and progression to end stage renal disease (ESRD) has a significant public health impact. Family studies suggest that the risk for CKD and ESRD is heritable. Unraveling the genetic underpinning of risk for these diseases may lead to the identification of novel mechanisms and thus diagnostic and therapeutic tools. We have previously identified 16 genetic markers in association with kidney function and prevalent CKD in general population studies. However, little is known about the relevance of these SNPs to the initial development of CKD or to ESRD risk. Therefore, we have now analyzed the association of these markers with the initiation of CKD in more than 26,000 individuals from the general population using serial estimations of kidney function, and with ESRD in four case-control studies in subjects of European ancestry (3,775 cases, 4,577 controls). We show that many of the 16 markers are also associated or show a strong trend towards association with initiation of CKD, while only 2 markers are nominally associated with ESRD. Further work is required to characterize the association of genetic determinants of different stages of CKD progression.

Trefoil factor 3 predicts incident chronic kidney disease: a case-control study nested within the Atherosclerosis Risk in Communities (ARIC) study

BACKGROUND

Early detection of individuals at high risk for chronic kidney disease (CKD) may aid prevention. Urinary levels of trefoil factor 3 (TFF3) are associated with acute kidney injury in animal models, but the association of TFF3 levels with incident CKD in humans is unknown.

METHODS

We conducted a case-control study nested within the Atherosclerosis Risk in Communities (ARIC) Study and the ARIC Carotid MRI Study to determine whether urinary TFF3 levels predict incident CKD over 8.6 years of follow-up. A total of 143 participants with incident CKD (eGFR decreasing by ≥25% to <60 ml/min/1.73 m(2)) were matched on age, sex and race to 143 non-cases.

RESULTS

Higher TFF3 levels at baseline were strongly associated with Black race, diabetes (both p = 0.002), and antihypertensive medication use (p = 0.02). Compared to participants with TFF3 levels in the lowest quartile, the odds ratio (OR) of incident CKD was 1.84 (95% confidence interval (CI): 0.80, 4.22) for individuals with TFF3 levels in the second quartile, 2.43 (95% CI: 1.06, 5.53) for the third quartile, and 2.77 (95% CI: 1.22, 6.28) for the fourth quartile (p trend = 0.02). Adjustment for covariates, including urinary albumin: creatinine ratio, did not markedly change the associations. Twofold higher TFF3 levels were strongly associated with incident CKD after adjustment for CKD risk factors (adjusted OR = 1.35; 95% CI: 1.11, 1.64).

CONCLUSIONS

Higher urinary TFF3 levels may indicate ongoing repair of damage in the kidney. Additional studies are needed to confirm whether TFF3 can be useful as a marker of increased risk for CKD.

Chronic kidney disease: novel insights from genome-wide association studies

Chronic kidney disease (CKD) is common, affecting about 10% of the general population, and causing significant morbidity and mortality. Apart from the risk conferred by traditional cardiovascular risk factors, there is a strong genetic component. The method of a genome-wide association study (GWAS) is a powerful hypothesis-free approach to unravel this component by association analyses of CKD with several million genetic variants distributed across the genome. Since the publication of the first GWAS in 2005, this method has led to the discovery of novel loci for numerous human common diseases and phenotypes. Here, we review the recent successes of meta-analyses of GWAS on renal phenotypes. UMOD, SHROOM3, STC1, LASS2, GCKR, ALMS1, TFDP2, DAB2, SLC34A1, VEGFA, PRKAG2, PIP5K1B, ATXN2/SH2B3, DACH1, UBE2Q2, and SLC7A9 were uncovered as loci associated with estimated glomerular filtration rate (eGFR) and CKD, and CUBN as a locus for albuminuria in cross-sectional data of general population studies. However, less than 1.5% of the total variance of eGFR and albuminuria is explained by the identified variants, and the relative risk for CKD is modified by at most 20% per locus. In African Americans, much of the risk for end-stage nondiabetic kidney disease is explained by common variants in the MYH9/APOL1 locus, and in individuals of European descent, variants in HLA-DQA1 and PLA(2)R1 implicate most of the risk for idiopathic membranous nephropathy. In contrast, genetic findings in the analysis of diabetic nephropathy are inconsistent. Uncovering variants explaining more of the genetically determined variability of kidney function is hampered by the multifactorial nature of CKD and different mechanisms involved in progressive CKD stages, and by the challenges in elucidating the role of low-frequency variants. Meta-analyses with larger sample sizes and analyses of longitudinal renal phenotypes using higher-resolution genotyping data are required to uncover novel loci associated with severe renal phenotypes.

Time-dependent impact of diabetes on the mortality of patients on renal replacement therapy: a population-based study in Germany (2002-2009)

AIMS

To estimate the impact of diabetes on the mortality of patients with incident renal replacement therapy (RRT).

METHODS

We assessed the mortality of 544 incident RRT patients aged ≥ 30 years between 2002 and 2009 (57.9% men, mean age 70.3 years, 49.6% patients with diabetes) by analyzing the data of all dialysis centers covering a German region. We compared the estimated time-dependent hazard ratios of patients with and without diabetes by using the Cox proportional-hazards regression model.

RESULTS

Overall, 319 patients had died (158 diabetic), approximately 50% after 3 years. Up to about 3 years, the mortality rate was lower in diabetic than in nondiabetic patients. Thereafter, the survival curves crossed (interaction diabetes × time, p = 0.002; adjusted hazard ratios for diabetes: baseline, 0.66; year 1, 0.84; year 2, 1.05; year 3, 1.33; year 4, 1.68). The results were similar in men and women; however, the interaction of diabetes and time was significant only in men (p = 0.004). Further significant risk factors of mortality were age, sex, initial central venous catheter, cardiovascular disease, and malignancy.

CONCLUSIONS

In this population-based study, the influence of diabetes was time-dependent, with a lower mortality in diabetic versus non-diabetic patients in the first three years but a higher mortality in these patients after 3 years. Results were similar in men and women.

Combined aliskiren-amlodipine treatment for hypertension in African Americans: clinical science and management issues

While it may seem at first that antihypertensive drug combinations run counter to the desire to 'personalize' the management of hypertension, the best combinations have predictable efficacy in different individuals and subpopulations. Race is probably not a valid surrogate for clinically meaningful genetic variation or guide to therapy. Most guidelines suggest similar blood pressure goals for different races but drug treatment recommendations have diverged. In the United States, race is not considered to be a major factor in drug choice, but in England and other countries, initial therapy with renin-angiotensin system blocking drugs is not recommended in Blacks. In this review we: (1) examine new trends in race-based research; (2) emphasize the weaknesses of race-based treatment recommendations; and (3) explore the effects of a new combination, renin inhibition (aliskiren) and amlodipine, in African Americans.

The implications of using adjusted versus unadjusted methods to measure health care disparities at the practice level

Reducing disparities in care requires that health care providers identify populations at risk for suboptimal quality of care. Stratified analyses are often used to examine disparities (eg, by race or sex). However, stratified analyses can be misleading if the variables are confounded. The authors examined disparities in quality within a large ambulatory care practice using both unadjusted and adjusted methods for 18 measures. In unadjusted analyses, differences in quality were identified for 9 measures by race. However, in analyses adjusted simultaneously for race, sex, age, socioeconomic status, and chronic medical conditions, racial differences were apparent for only 4 measures. Women received lower quality care for 4 measures in both unadjusted and adjusted analyses. The pattern of observed disparities can differ significantly based on whether unadjusted or adjusted methods are applied. Health care organizations should consider the routine use of adjusted methods to measure disparities in order to better inform disparity reduction initiatives.

Glycated hemoglobin and the risk of kidney disease and retinopathy in adults with and without diabetes

OBJECTIVE

Glycated hemoglobin was recently recommended for use as a diagnostic test for diabetes. We examined the association between 2010 American Diabetes Association diagnostic cut points for glycated hemoglobin and microvascular outcomes (chronic kidney disease, end-stage renal disease [ESRD], and retinopathy) and formally tested for the presence of risk thresholds in the relationships of glycated hemoglobin with these outcomes.

RESEARCH DESIGN AND METHODS

Prospective cohort and cross-sectional analyses of 11,357 participants (773 with a history of diagnosed diabetes) from the Atherosclerosis Risk in Communities (ARIC) Study.

RESULTS

During a median of 14 years of follow-up of individuals without diagnosed diabetes at baseline, clinical categories of glycated hemoglobin were associated with risk of chronic kidney disease, with adjusted hazard ratios (HRs) of 1.12 (0.94-1.34) and 1.39 (1.04-1.85) for glycated hemoglobin 5.7-6.4% and ≥6.5%, respectively, as compared with <5.7% (P trend = 0.002). The corresponding HRs for ESRD were 1.51 (0.82-2.76) and 1.98 (0.83-4.73), respectively (P trend = 0.047). In the absence of diagnosed diabetes, glycated hemoglobin was cross sectionally associated with the presence of moderate/severe retinopathy, with adjusted odds ratios of 1.42 (0.69-2.92) and 2.91 (1.19-7.11) for glycated hemoglobin 5.7-<6.5% and ≥6.5%, respectively, compared with <5.7% (P trend = 0.011). Risk associations were stronger among individuals with a history of diabetes. We did not observe significant thresholds in the associations of glycated hemoglobin with kidney disease risk or retinopathy.

CONCLUSIONS

These data from a community-based, biracial population support the use of new 2010 American Diabetes Association glycated hemoglobin cut points for the diagnosis of diabetes.

Prediction of ESRD and death among people with CKD: the Chronic Renal Impairment in Birmingham (CRIB) prospective cohort study

Background

Validated prediction scores are required to assess the risks of end-stage renal disease (ESRD) and death in individuals with chronic kidney disease (CKD).

Study Design

Prospective cohort study with validation in a separate cohort.

Setting & Participants

Cox regression was used to assess the relevance of baseline characteristics to risk of ESRD (mean follow-up, 4.1 years) and death (mean follow-up, 6.0 years) in 382 patients with stages 3-5 CKD not initially on dialysis therapy in the Chronic Renal Impairment in Birmingham (CRIB) Study. Resultant risk prediction equations were tested in a separate cohort of 213 patients with CKD (the East Kent cohort).

Factors

44 baseline characteristics (including 30 blood and urine assays).

Outcomes

ESRD and all-cause mortality.

Results

In the CRIB cohort, 190 patients reached ESRD (12.1%/y) and 150 died (6.5%/y). Each 30% lower baseline estimated glomerular filtration rate was associated with a 3-fold higher ESRD rate and a 1.3-fold higher death rate. After adjustment for each other, only baseline creatinine level, serum phosphate level, urinary albumin-creatinine ratio, and female sex remained strongly (P < 0.01) predictive of ESRD. For death, age, N-terminal pro-brain natriuretic peptide, troponin T level, and cigarette smoking remained strongly predictive of risk. Using these factors to predict outcomes in the East Kent cohort yielded an area under the receiver operating characteristic curve (ie, C statistic) of 0.91 (95% CI, 0.87-0.96) for ESRD and 0.82 (95% CI, 0.75-0.89) for death.

Limitations

Other important factors may have been missed because of limited study power.

Conclusions

Simple laboratory measures of kidney and cardiac function plus age, sex, and smoking history can be used to help identify patients with CKD at highest risk of ESRD and death. Larger cohort studies are required to further validate these results.

Genome-wide association studies in nephrology research

Kidney diseases constitute a serious public health burden worldwide, with substantial associated morbidity and mortality. The role of a genetic contribution to kidney disease is supported by heritability studies of kidney function measures, the presence of monogenic diseases with renal manifestations, and familial aggregation studies of complex kidney diseases, such as chronic kidney disease. Because complex diseases arise from the combination of multiple genetic and environmental risk factors, the identification of underlying genetic susceptibility variants has been challenging. Recently, genome-wide association studies have emerged as a method to conduct searches for such susceptibility variants. They have successfully identified genomic loci that contain variants associated with kidney diseases and measures of kidney function. For example, common variants in the UMOD and PRKAG2 genes are associated with risk of chronic kidney disease; variants in CLDN14 with risk of kidney stone disease; and variants in or near SHROOM3, STC1, LASS2, GCKR, NAT8/ALMS1, TFDP2, DAB2, SLC34A1, VEGFA, FAM122A/PIP5K1B, ATXN2, DACH1, UBE2Q2/FBXO22, and SLC7A9, with differences in glomerular filtration rate. The purpose of this review is to provide an overview of the genome-wide association study method as it relates to nephrology research and summarize recent findings in the field. Results from genome-wide association studies of renal phenotypes represent a first step toward improving our knowledge about underlying mechanisms of kidney function and disease and ultimately may aid in the improved treatment and prevention of kidney diseases.

Albuminuria and estimated glomerular filtration rate independently associate with acute kidney injury

Acute kidney injury (AKI) is increasingly common and a significant contributor to excess death in hospitalized patients. CKD is an established risk factor for AKI; however, the independent graded association of urine albumin excretion with AKI is unknown. We analyzed a prospective cohort of 11,200 participants in the Atherosclerosis Risk in Communities (ARIC) study for the association between baseline urine albumin-to-creatinine ratio and estimated GFR (eGFR) with hospitalizations or death with AKI. The incidence of AKI events was 4.0 per 1000 person-years of follow-up. Using participants with urine albumin-to-creatinine ratios <10 mg/g as a reference, the relative hazards of AKI, adjusted for age, gender, race, cardiovascular risk factors, and categories of eGFR were 1.9 (95% CI, 1.4 to 2.6), 2.2 (95% CI, 1.6 to 3.0), and 4.8 (95% CI, 3.2 to 7.2) for urine albumin-to-creatinine ratio groups of 11 to 29 mg/g, 30 to 299 mg/g, and ≥300 mg/g, respectively. Similarly, the overall adjusted relative hazard of AKI increased with decreasing eGFR. Patterns persisted within subgroups of age, race, and gender. In summary, albuminuria and eGFR have strong, independent associations with incident AKI.

Early intervention strategies to lower cardiovascular risk in early nephropathy: focus on dyslipidemia

Patients with chronic kidney disease (CKD) are at high cardiovascular risk and we can consider them to have a risk equivalent to coronary heart disease, putting them into the high-risk category. A mixed dyslipidemia with high triglyceride levels; low high-density lipoprotein (HDL) levels; and small, dense low-density lipoprotein (LDL) particles is a common pattern in patients with CKD, contributing to their high cardiovascular disease (CVD) risk. A treatment strategy to reduce LDL cholesterol to the current high-risk category goals reduces risk similar to patients without CKD. Emerging evidence suggests that targeting non-HDL cholesterol can have the potential to bring about further CVD risk reduction. Non-HDL cholesterol should be a secondary target for all patients with CKD. Further studies are needed to determine the magnitude of the risk reduction we can expect to gain by targeting non-HDL cholesterol and the most effective way to treat this target.

Incidence of renal replacement therapy (RRT) in the diabetic compared with the non-diabetic population in a German region, 2002-08

BACKGROUND

This study was conducted to estimate incidences of renal replacement therapy (RRT) in the diabetic and non-diabetic populations in Germany, as well as relative and attributable risks of RRT due to diabetes.

METHODS

Using the data of a regional dialysis centre (region population of 310 000), we assessed all incident RRT patients aged 30 years or older in 2002-08. We estimated sex- and age-specific and -standardized incidences of RRT in the diabetic and non-diabetic populations, which were estimated by applying diabetes prevalences from a population-based study, and relative and attributable risks due to diabetes.

RESULTS

Of all subjects with incident RRT (n = 544), 49.6% had diabetes. Fifty-eight percent were male, mean age (SD) was 70.3 years (11.4 years). Incidences per 100 000 person-years (standardized to the 2004 German population) in the diabetic and the non-diabetic populations were 213.7 [95% confidence interval (95% CI), 159.5-267.8] and 26.9 (95% CI, 22.5-31.3) in men and 130.2 (95% CI, 65.6-194.9) and 16.4 (95% CI, 13.5-19.3) in women, respectively. Standardized relative risks were 7.9 (5.9-10.8) in men and 8.0 (4.7-13.5) in women. There was a significant interaction between age and diabetes, with lower relative risks in higher ages. Attributable risks among diabetic individuals were 0.87 in men and women, and population-attributable risks were 0.41 and 0.35 in men and women, respectively.

CONCLUSIONS

In this population-based study in a German region, we found the relative risk of RRT in the estimated adult diabetic population to be 8-fold increased compared with the non-diabetic population. A high proportion of the RRT risk can be attributed to diabetes in the diabetic as well as in the whole population.

Association of uric acid with change in kidney function in healthy normotensive individuals

BACKGROUND

Despite recent evidence, the role of uric acid as a causal factor in the pathogenesis and progression of kidney disease remains controversial, partly because of the inclusion in epidemiologic studies of patients with hypertension, diabetes, and/or proteinuria.

STUDY DESIGN

Prospective observational cohort.

SETTING & PARTICIPANTS

900 healthy normotensive adult blood donors (153 women, 747 men) evaluated at baseline and after 5 years.

PREDICTOR

Serum uric acid level.

OUTCOMES

Decrease in estimated glomerular filtration rate (eGFR) >10 mL/min/1.73 m(2), computed using the Modification of Diet in Renal Disease (MDRD) Study equation, with secondary analyses examining similar decreases using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Cockcroft-Gault equations.

RESULTS

During a median follow-up of 59 months, eGFR decreased from 97 +/- 16 to 88 +/- 14 mL/min/1.73 m(2). Higher serum uric acid levels were associated with a greater likelihood of eGFR decrease in both women and men (HR, 1.13 [95% CI, 1.04-1.39] per each 1-mg/dL increase in uric acid level); in multivariable analyses adjusting for age, sex, body mass index, blood glucose level, total cholesterol level, mean blood pressure, urine albumin-creatinine ratio, and serum triglyceride level, the association remained highly significant (HR, 1.28 [95% CI, 1.12-1.48]). Results were similar using different estimating equations and when the association was examined in sex-specific subgroups.

LIMITATIONS

Analyses were based on a single baseline uric acid measurement. Women are underrepresented.

CONCLUSIONS

In healthy normotensive individuals, serum uric acid level is an independent risk factor for decreased kidney function.

Renal dysfunction in chronic liver disease

This article is one of ten reviews selected from the Yearbook of Intensive Care and Emergency Medicine 2010 (Springer Verlag) and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/yearbook. Further information about the Yearbook of Intensive Care and Emergency Medicine is available from http://www.springer.com/series/2855.