Changes in Natriuretic Peptide Levels and Subsequent Kidney Function Decline in SPRINT.

RATIONALE & OBJECTIVE: Novel approaches to the assessment of kidney disease risk during hypertension treatment are needed because of the uncertainty of how intensive blood pressure (BP) lowering impacts kidney outcomes. We determined whether longitudinal N-terminal pro-B-type natriuretic peptide (NT-proBNP) measurements during hypertension treatment are associated with kidney function decline. STUDY DESIGN: Prospective observational study. SETTING & PARTICIPANTS: 8,005 SPRINT (Systolic Blood Pressure Intervention Trial) participants with NT-proBNP measurements at baseline and 1 year. EXPOSURE: 1-year change in NT-proBNP categorized as a ≥25% decrease, ≥25% increase, or <25% change (stable). OUTCOME: Annualized change in estimated glomerular filtration rate (eGFR) and ≥30% decrease in eGFR. ANALYTICAL APPROACH: Linear mixed-effect and logistic regression models were used to evaluate the association of changes in NT-proBNP with subsequent annualized change in eGFR and ≥30% decrease in eGFR, respectively. Analyses were stratified by baseline chronic kidney disease (CKD) status. RESULTS: Compared with stable 1-year NT-proBNP levels, a ≥25% decrease in NT-proBNP was associated with a slower decrease in eGFR in participants with CKD (adjusted difference, 1.09%/y; 95% CI, 0.35-1.83) and without CKD (adjusted difference, 0.51%/y; 95% CI, 0.21-0.81; P = 0.4 for interaction). Meanwhile, a ≥25% increase in NT-proBNP in participants with CKD was associated with a faster decrease in eGFR (adjusted difference, -1.04%/y; 95% CI, -1.72 to -0.36) and risk of a ≥30% decrease in eGFR (adjusted odds ratio, 1.44; 95% CI, 1.06-1.96); associations were stronger in participants with CKD than in participants without CKD (P = 0.01 and P < 0.001 for interaction, respectively). Relationships were similar irrespective of the randomized BP arm in SPRINT (P > 0.2 for interactions). LIMITATIONS: Persons with diabetes and proteinuria >1 g/d were excluded. CONCLUSIONS: Changes in NT-proBNP during BP treatment are independently associated with subsequent kidney function decline, particularly in people with CKD. Future studies should assess whether routine NT-proBNP measurements may be useful in monitoring kidney risk during hypertension treatment. PLAIN-LANGUAGE SUMMARY: N-terminal pro-B-type natriuretic peptide (NT-proBNP) is a biomarker in the blood that reflects mechanical stress on the heart. Measuring NT-proBNP may be helpful in assessing the risk of long-term losses of kidney function. In this study, we investigated the association of changes in NT-proBNP with subsequent kidney function among individuals with and without chronic kidney disease. We found that increases in NT-proBNP are associated with a faster rate of decline of kidney function, independent of baseline kidney measures. The associations were more pronounced in individuals with chronic kidney disease. Our results advance the notion of considering NT-proBNP as a dynamic tool for assessing kidney disease risk.

Markers of Kidney Tubular Secretion and Risk of Adverse Events in SPRINT Participants with CKD.

BACKGROUND: Kidney tubular secretion is an essential mechanism for clearing many common antihypertensive drugs and other metabolites and toxins. It is unknown whether novel measures of tubular secretion are associated with adverse events (AEs) during hypertension treatment. METHODS: Among 2089 SPRINT (Systolic Blood Pressure Intervention Trial) participants with baseline eGFR <60 ml/min per 1.73 m2, we created a summary secretion score by averaging across the standardized spot urine-to-plasma ratios of ten novel endogenous tubular secretion measures, with lower urine-to-plasma ratios reflecting worse tubular secretion. Multivariable Cox proportional hazards models were used to evaluate associations between the secretion score and risk of a composite of prespecified serious AEs (hypotension, syncope, bradycardia, AKI, electrolyte abnormalities, and injurious falls). The follow-up protocol for SPRINT routinely assessed two laboratory monitoring AEs (hyperkalemia and hypokalemia). RESULTS: Overall, 30% of participants experienced at least one AE during a median follow-up of 3.0 years. In multivariable models adjusted for eGFR and albuminuria, lower (worse) secretion scores at baseline were associated with greater risk of the composite AE outcome (hazard ratio per 1-SD lower secretion score, 1.16; 95% confidence interval, 1.04 to 1.27). In analyses of the individual AEs, lower secretion score was associated with significantly greater risk of AKI, serious electrolyte abnormalities, and ambulatory hyperkalemia. Associations were similar across randomized treatment assignment groups. CONCLUSION: Among SPRINT participants with CKD, worse tubular secretion was associated with greater risk of AEs, independent of eGFR and albuminuria.

Implementing the European Renal Best Practice Guidelines suggests that prediction equations work well to differentiate risk of end-stage renal disease vs. death in older patients with low estimated glomerular filtration rate.

Recent European guidelines suggest using the kidney failure risk equation (KFRE) and mortality risk equation for kidney disease (MREK) to guide decisions on whether elderly patients with chronic kidney disease should be referred early for dialysis preparation. However, the concurrent use of the two risk equations has not been validated. To do so we evaluated 1,188 individuals over five years with estimated glomerular filtration rate (eGFR) under 45ml/min/1.73m2 and age over 65 years from the Norwegian population based HUNT study. Forty-two patients started renal replacement therapy and 462 died as their first clinical event. The KFRE was well calibrated (mean risk estimate 4.9% vs observed 3.5%) with high diagnostic accuracy (C-statistics 0.93). The MREK underestimated death risk in those with lower risk (mean risk estimate 30.1% vs observed 38.9%) and had moderate diagnostic accuracy (C-statistics 0.71). Only 31 individuals had estimated end stage kidney disease (ESRD) risk greater than death risk, and most experienced ESRD before death. Only two of 598 patients over 80 years old, and ten of 1,063 with eGFR 25-45ml/min/1.73m2 at baseline experienced ESRD. Decision curve analysis demonstrated that for risk adverse patients, deferring ESRD preparation may be appropriate until predicted ESRD risk exceeds predicted death risk. For those preferring a more aggressive approach, referral when eGFR is under 25 ml/min/1.73m2 may be beneficial if age remains under 80 years. Thus, the risk of ESRD is low compared to the risk of death in many older patients with chronic kidney disease stage 3b or worse, and combination of predicted ESRD and death risks, eGFR levels, age, and the patient`s valuations of harm and benefit can be helpful for deciding when to start dialysis preparations.

Relationship of Estimated GFR and Albuminuria to Concurrent Laboratory Abnormalities: An Individual Participant Data Meta-analysis in a Global Consortium.

RATIONALE & OBJECTIVE: Chronic kidney disease (CKD) is complicated by abnormalities that reflect disruption in filtration, tubular, and endocrine functions of the kidney. Our aim was to explore the relationship of specific laboratory result abnormalities and hypertension with the estimated glomerular filtration rate (eGFR) and albuminuria CKD staging framework. STUDY DESIGN: Cross-sectional individual participant-level analyses in a global consortium. SETTING & STUDY POPULATIONS: 17 CKD and 38 general population and high-risk cohorts. SELECTION CRITERIA FOR STUDIES: Cohorts in the CKD Prognosis Consortium with data for eGFR and albuminuria, as well as a measurement of hemoglobin, bicarbonate, phosphorus, parathyroid hormone, potassium, or calcium, or hypertension. DATA EXTRACTION: Data were obtained and analyzed between July 2015 and January 2018. ANALYTICAL APPROACH: We modeled the association of eGFR and albuminuria with hemoglobin, bicarbonate, phosphorus, parathyroid hormone, potassium, and calcium values using linear regression and with hypertension and categorical definitions of each abnormality using logistic regression. Results were pooled using random-effects meta-analyses. RESULTS: The CKD cohorts (n=254,666 participants) were 27% women and 10% black, with a mean age of 69 (SD, 12) years. The general population/high-risk cohorts (n=1,758,334) were 50% women and 2% black, with a mean age of 50 (16) years. There was a strong graded association between lower eGFR and all laboratory result abnormalities (ORs ranging from 3.27 [95% CI, 2.68-3.97] to 8.91 [95% CI, 7.22-10.99] comparing eGFRs of 15 to 29 with eGFRs of 45 to 59mL/min/1.73m2), whereas albuminuria had equivocal or weak associations with abnormalities (ORs ranging from 0.77 [95% CI, 0.60-0.99] to 1.92 [95% CI, 1.65-2.24] comparing urinary albumin-creatinine ratio > 300 vs < 30mg/g). LIMITATIONS: Variations in study era, health care delivery system, typical diet, and laboratory assays. CONCLUSIONS: Lower eGFR was strongly associated with higher odds of multiple laboratory result abnormalities. Knowledge of risk associations might help guide management in the heterogeneous group of patients with CKD.

Serum potassium and adverse outcomes across the range of kidney function: a CKD Prognosis Consortium meta-analysis.

Aims: Both hypo- and hyperkalaemia can have immediate deleterious physiological effects, and less is known about long-term risks. The objective was to determine the risks of all-cause mortality, cardiovascular mortality, and end-stage renal disease associated with potassium levels across the range of kidney function and evaluate for consistency across cohorts in a global consortium. Methods and results: We performed an individual-level data meta-analysis of 27 international cohorts [10 general population, 7 high cardiovascular risk, and 10 chronic kidney disease (CKD)] in the CKD Prognosis Consortium. We used Cox regression followed by random-effects meta-analysis to assess the relationship between baseline potassium and adverse outcomes, adjusted for demographic and clinical characteristics, overall and across strata of estimated glomerular filtration rate (eGFR) and albuminuria. We included 1 217 986 participants followed up for a mean of 6.9 years. The average age was 55 ± 16 years, average eGFR was 83 ± 23 mL/min/1.73 m2, and 17% had moderate- to-severe increased albuminuria levels. The mean baseline potassium was 4.2 ± 0.4 mmol/L. The risk of serum potassium of >5.5 mmol/L was related to lower eGFR and higher albuminuria. The risk relationship between potassium levels and adverse outcomes was U-shaped, with the lowest risk at serum potassium of 4-4.5 mmol/L. Compared with a reference of 4.2 mmol/L, the adjusted hazard ratio for all-cause mortality was 1.22 [95% confidence interval (CI) 1.15-1.29] at 5.5 mmol/L and 1.49 (95% CI 1.26-1.76) at 3.0 mmol/L. Risks were similar by eGFR, albuminuria, renin-angiotensin-aldosterone system inhibitor use, and across cohorts. Conclusions: Outpatient potassium levels both above and below the normal range are consistently associated with adverse outcomes, with similar risk relationships across eGFR and albuminuria.

Long-term trends in the prevalence of chronic kidney disease and the influence of cardiovascular risk factors in Norway.

Surveillance of chronic kidney disease (CKD) prevalence over time and information on how changing risk factors influence this trend are needed to evaluate the effects of general practice and public health interventions. Because very few studies addressed this, we studied the total adult population of a demographically stable county representative of Norway using cross-sectional studies 10 years apart (Nord-Trøndelag Health Study (HUNT)2 and Nord-Trøndelag Health Study (HUNT)3, 65,237 and 50,586 participants, respectively). Thorough quality-control procedures and comparisons of methods over time excluded analytical drift, and multiple imputations of missing data combined with nonattendance weights contributed to unbiased estimates. CKD prevalence remained stable in Norway from 1995 through 1997 (11.3%) to 2006 through 2008 (11.1%). The association of survey period with CKD prevalence was modified by a strong decrease in blood pressure, more physical activity, and lower cholesterol levels. Without these improvements, a 2.8, 0.7, and 0.6 percentage points higher CKD prevalence could have been expected, respectively. In contrast, the prevalence of diabetes and obesity increased moderately, but the proportion of diabetic patients with CKD decreased significantly (from 33.4% to 28.6%). A CKD prevalence of 1 percentage point lower would have been expected without these changes. Thus, CKD prevalence remained stable in Norway for more than a decade in association with marked improvements in blood pressure, lipid levels, and physical activity and despite modest increases in diabetes and obesity.

Multinational Assessment of Accuracy of Equations for Predicting Risk of Kidney Failure: A Meta-analysis.

IMPORTANCE: Identifying patients at risk of chronic kidney disease (CKD) progression may facilitate more optimal nephrology care. Kidney failure risk equations, including such factors as age, sex, estimated glomerular filtration rate, and calcium and phosphate concentrations, were previously developed and validated in 2 Canadian cohorts. Validation in other regions and in CKD populations not under the care of a nephrologist is needed. OBJECTIVE: To evaluate the accuracy of the risk equations across different geographic regions and patient populations through individual participant data meta-analysis. DATA SOURCES: Thirty-one cohorts, including 721,357 participants with CKD stages 3 to 5 in more than 30 countries spanning 4 continents, were studied. These cohorts collected data from 1982 through 2014. STUDY SELECTION: Cohorts participating in the CKD Prognosis Consortium with data on end-stage renal disease. DATA EXTRACTION AND SYNTHESIS: Data were obtained and statistical analyses were performed between July 2012 and June 2015. Using the risk factors from the original risk equations, cohort-specific hazard ratios were estimated and combined using random-effects meta-analysis to form new pooled kidney failure risk equations. Original and pooled kidney failure risk equation performance was compared, and the need for regional calibration factors was assessed. MAIN OUTCOMES AND MEASURES: Kidney failure (treatment by dialysis or kidney transplant). RESULTS: During a median follow-up of 4 years of 721,357 participants with CKD, 23,829 cases kidney failure were observed. The original risk equations achieved excellent discrimination (ability to differentiate those who developed kidney failure from those who did not) across all cohorts (overall C statistic, 0.90; 95% CI, 0.89-0.92 at 2 years; C statistic at 5 years, 0.88; 95% CI, 0.86-0.90); discrimination in subgroups by age, race, and diabetes status was similar. There was no improvement with the pooled equations. Calibration (the difference between observed and predicted risk) was adequate in North American cohorts, but the original risk equations overestimated risk in some non-North American cohorts. Addition of a calibration factor that lowered the baseline risk by 32.9% at 2 years and 16.5% at 5 years improved the calibration in 12 of 15 and 10 of 13 non-North American cohorts at 2 and 5 years, respectively (P = .04 and P = .02). CONCLUSIONS AND RELEVANCE: Kidney failure risk equations developed in a Canadian population showed high discrimination and adequate calibration when validated in 31 multinational cohorts. However, in some regions the addition of a calibration factor may be necessary.

Urinary proteomics in chronic kidney disease: diagnosis and risk of progression beyond albuminuria.

BACKGROUND: The contrast between a high prevalence of chronic kidney disease (CKD) and the low incidence of end-stage renal disease highlights the need for new biomarkers of progression beyond albuminuria testing. Urinary proteomics is a promising method, but more studies focusing on progression rate and patients with hypertensive nephropathy are needed. RESULTS: We analyzed urine samples with capillary electrophoresis coupled to a mass-spectrometer from 18 well characterized patients with CKD stage 4-5 (of whom six with hypertensive nephropathy) and 17 healthy controls. Classification scores based on a previously developed panel of 273 urinary peptides were calculated and compared to urine albumin dipstick results. Urinary proteomics classified CKD with a sensitivity of 0.95 and specificity of 1.00. Overall diagnostic accuracy (area under ROC curve) was 0.98, which was better than for albuminuria (0.85, p = 0.02). Results for hypertensive nephropathy were similar to other CKD diagnoses. Adding the proteomic score to an albuminuria model improved detection of rapid kidney function decline (>4 ml/min/1.73 m(2) per year) substantially: area under ROC curve increased from 0.762 to 0.909 (p = 0.042), and 38% of rapid progressors were correctly reclassified to a higher risk and 55% of slow progressors were correctly reclassified to a lower risk category. Reduced excretion of collagen types I-III, uromodulin, and other indicators of interstitial inflammation, fibrosis and tubular dysfunction were associated with CKD diagnosis and rapid progression. Patients with hypertensive nephropathy displayed the same findings as other types of CKD. CONCLUSIONS: Urinary proteomic analyses had a high diagnostic accuracy for CKD, including hypertensive nephropathy, and strongly improved identification of patients with rapid kidney function decline beyond albuminuria testing.

The accuracy of predicting cardiovascular death based on one compared to several albuminuria values.

Albuminuria is a well-documented predictor of cardiovascular (CV) mortality. However, day-to-day variability is substantial, and there is no consensus on the number of urine samples required for risk prediction. To resolve this we followed 9158 adults from the population-based Nord-Trøndelag Health Study for 13 years (Second HUNT Study). The predictive performance of models for CV death based on Framingham variables plus 1 versus 3 albumin-creatinine ratio (ACR) was assessed in participants who provided 3 urine samples. There was no improvement in discrimination, calibration, or reclassification when using ACR as a continuous variable. Difference in Akaike information criterion indicated an uncertain improvement in overall fit for the model with the mean of 3 urine samples. Criterion analyses on dichotomized albuminuria information sustained 1 sample as sufficient for ACR levels down to 1.7 mg/mmol. At lower levels, models with 3 samples had a better overall fit. Likewise, in survival analyses, 1 sample was enough to show a significant association to CV mortality for ACR levels above 1.7 mg/mmol (adjusted hazard ratio 1.37; 95% CI 1.15-1.63). For lower ACR levels, 2 or 3 positive urine samples were needed for significance. Thus, multiple urine sampling did not improve CV death prediction when using ACR as a continuous variable. For cutoff ACR levels of 1.0 mg/mmol or less, additional urine samples were required, and associations were stronger with increasing number of samples.

Association of mild to moderate chronic kidney disease with venous thromboembolism: pooled analysis of five prospective general population cohorts.

BACKGROUND: Recent findings suggest that chronic kidney disease (CKD) may be associated with an increased risk of venous thromboembolism (VTE). Given the high prevalence of mild-to-moderate CKD in the general population, in depth analysis of this association is warranted. METHODS AND RESULTS: We pooled individual participant data from 5 community-based cohorts from Europe (second Nord-Trøndelag Health Study [HUNT2], Prevention of Renal and Vascular End-stage Disease [PREVEND], and the Tromsø study) and the United States (Atherosclerosis Risks in Communities [ARIC] and Cardiovascular Health Study [CHS]) to assess the association of estimated glomerular filtration rate (eGFR), albuminuria, and CKD with objectively verified VTE. To estimate adjusted hazard ratios for VTE, categorical and continuous spline models were fit by using Cox regression with shared-frailty or random-effect meta-analysis. A total of 1178 VTE events occurred over 599 453 person-years follow-up. Relative to eGFR 100 mL/min per 1.73 m(2), hazard ratios for VTE were 1.29 (95% confidence interval, 1.04-1.59) for eGFR 75, 1.31 (1.00-1.71) for eGFR 60, 1.82 (1.27-2.60) for eGFR 45, and 1.95 (1.26-3.01) for eGFR 30 mL/min per 1.73 m(2). In comparison with an albumin-to-creatinine ratio (ACR) of 5.0 mg/g, the hazard ratios for VTE were 1.34 (1.04-1.72) for ACR 30 mg/g, 1.60 (1.08-2.36) for ACR 300 mg/g, and 1.92 (1.19-3.09) for ACR 1000 mg/g. There was no interaction between clinical categories of eGFR and ACR (P=0.20). The adjusted hazard ratio for CKD, defined as eGFR <60 mL/min per 1.73 m(2) or albuminuria ≥30 mg/g, (versus no CKD) was 1.54 (95% confidence interval, 1.15-2.06). Associations were consistent in subgroups according to age, sex, and comorbidities, and for unprovoked versus provoked VTE, as well. CONCLUSIONS: Both eGFR and ACR are independently associated with increased risk of VTE in the general population, even across the normal eGFR and ACR ranges.

Age and association of kidney measures with mortality and end-stage renal disease.

CONTEXT: Chronic kidney disease (CKD) is prevalent in older individuals, but the risk implications of low estimated glomerular filtration rate (eGFR) and high albuminuria across the full age range are controversial. OBJECTIVE: To evaluate possible effect modification (interaction) by age of the association of eGFR and albuminuria with clinical risk, examining both relative and absolute risks. DESIGN, SETTING, AND PARTICIPANTS: Individual-level meta-analysis including 2,051,244 participants from 33 general population or high-risk (of vascular disease) cohorts and 13 CKD cohorts from Asia, Australasia, Europe, and North/South America, conducted in 1972-2011 with a mean follow-up time of 5.8 years (range, 0-31 years). MAIN OUTCOME MEASURES: Hazard ratios (HRs) of mortality and end-stage renal disease (ESRD) according to eGFR and albuminuria were meta-analyzed across age categories after adjusting for sex, race, cardiovascular disease, diabetes, systolic blood pressure, cholesterol, body mass index, and smoking. Absolute risks were estimated using HRs and average incidence rates. RESULTS: Mortality (112,325 deaths) and ESRD (8411 events) risks were higher at lower eGFR and higher albuminuria in every age category. In general and high-risk cohorts, relative mortality risk for reduced eGFR decreased with increasing age; eg, adjusted HRs at an eGFR of 45 mL/min/1.73 m2 vs 80 mL/min/1.73 m2 were 3.50 (95% CI, 2.55-4.81), 2.21 (95% CI, 2.02-2.41), 1.59 (95% CI, 1.42-1.77), and 1.35 (95% CI, 1.23-1.48) in age categories 18-54, 55-64, 65-74, and ≥75 years, respectively (P <.05 for age interaction). Absolute risk differences for the same comparisons were higher at older age (9.0 [95% CI, 6.0-12.8], 12.2 [95% CI, 10.3-14.3], 13.3 [95% CI, 9.0-18.6], and 27.2 [95% CI, 13.5-45.5] excess deaths per 1000 person-years, respectively). For increased albuminuria, reduction of relative risk with increasing age was less evident, while differences in absolute risk were higher in older age categories (7.5 [95% CI, 4.3-11.9], 12.2 [95% CI, 7.9-17.6], 22.7 [95% CI, 15.3-31.6], and 34.3 [95% CI, 19.5-52.4] excess deaths per 1000 person-years, respectively by age category, at an albumin-creatinine ratio of 300 mg/g vs 10 mg/g). In CKD cohorts, adjusted relative hazards of mortality did not decrease with age. In all cohorts, ESRD relative risks and absolute risk differences at lower eGFR or higher albuminuria were comparable across age categories. CONCLUSIONS: Both low eGFR and high albuminuria were independently associated with mortality and ESRD regardless of age across a wide range of populations. Mortality showed lower relative risk but higher absolute risk differences at older age.

Direction- and Angle-Assisted Buttonhole Cannulation of Arteriovenous Fistula in Hemodialysis Patients: A Multicenter Randomized Controlled Trial.

RATIONALE & OBJECTIVE: Arteriovenous fistula cannulation with the buttonhole technique is often preferred by patients but has been associated with an increased infection risk. Guidelines disagree on whether it should be abandoned, thus we assessed a technologically simple method to facilitate gentler arteriovenous fistula cannulation with potentially less discomfort and damage to the epithelial lining of the buttonhole tract. STUDY DESIGN: 8-week, prospective, open-label, randomized controlled trial. SETTING & PARTICIPANTS: Patients with buttonhole tracts receiving hemodialysis at 7 dialysis centers in Norway were randomized to the intervention group (43 patients, 658 cannulations) or control group (40 patients, 611 cannulations). INTERVENTION: Direction and angle of the established buttonhole tract were marked on the forearm skin in the intervention group, whereas the control group had no structured cannulation information system. OUTCOMES: The primary outcome was successful cannulation, defined as correct placement of both blunt needles at the first attempt without needing to change needles, perform extra perforations, or reposition the needle. The secondary outcomes were patient-reported difficulty of cannulation (verbal rating scale: 1 = very easy, 6 = impossible) and intensity of pain (numeric rating scale: 0 = no pain, 10 = unbearable pain). RESULTS: After a 2-week run-in period, successful cannulation was achieved in 73.9% and 74.8% of the patients in the intervention and control groups, respectively (relative risk [RR], 0.99; 95% CI, 0.87-1.12; P = 0.85). However, the probability of a difficult arterial cannulation (verbal rating scale, 3-6) was significantly lower in the intervention group (RR, 0.69; 95% CI, 0.55-0.85; P = 0.001). There were no improvements for venous cannulations. Furthermore, the probability of a painful cannulation (numeric rating scale, 3-10) was lower in the intervention group (RR, 0.72; 95% CI, 0.51-1.02; P = 0.06). LIMITATIONS: Unable to evaluate hard end points such as infections and thrombosis owing to the small sample size. CONCLUSIONS: Marking direction and angle of cannulation did not improve cannulation success rates; however, patients more often reported an unproblematic procedure and less pain. FUNDING: None. TRIAL REGISTRATION: ClinicalTrials.gov (NCT01536548).

Clinical Risk Factors For Kidney Tubule Biomarker Abnormalities Among Hypertensive Adults With Reduced eGFR in the SPRINT Trial.

BACKGROUND: Urine biomarkers of kidney tubule health may distinguish aspects of kidney damage that cannot be captured by current glomerular measures. Associations of clinical risk factors with specific kidney tubule biomarkers have not been evaluated in detail. METHODS: We performed a cross-sectional study in the Systolic Blood Pressure Intervention Trial among 2,436 participants with a baseline estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m2. Associations between demographic and clinical characteristics with urine biomarkers of kidney tubule health were evaluated using simultaneous multivariable linear regression of selected variables. RESULTS: Each standard deviation higher age (9 years) was associated with 13% higher levels of chitinase-3-like protein-1 (YKL-40), indicating higher levels of tubulointerstitial inflammation and repair. Men had 31% higher levels of alpha-1 microglobulin and 16% higher levels of beta-2 microglobulin, reflecting worse tubule resorptive function. Black race was associated with significantly higher levels of neutrophil gelatinase-associated lipocalin (12%) and lower kidney injury molecule-1 (26%) and uromodulin (22%). Each standard deviation (SD) higher systolic blood pressure (SBP) (16 mmHg) was associated with 10% higher beta-2 microglobulin and 10% higher alpha-1 microglobulin, reflecting lower tubule resorptive function. CONCLUSIONS: Clinical and demographic characteristics, such as race, sex, and elevated SBP, are associated with unique profiles of tubular damage, which could reflect under-recognized patterns of kidney tubule disease among persons with decreased eGFR.

Estimated Kidney Tubular Secretion and Kidney, Cardiovascular, and Mortality Outcomes in CKD: The Systolic Blood Pressure Intervention Trial.

Rational & Objective: Many drugs, metabolites, and toxins are cleared by the kidneys via tubular secretion. Whether novel endogenous measures of tubular secretion provide information about kidney, cardiovascular, and mortality risk is uncertain. Study Design: Longitudinal subgroup analysis of clinical trial participants. Setting & Participants: 2,089 Systolic Blood Pressure Intervention Trial participants with estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2 at baseline. Exposure: Summary score incorporating urine-to-plasma ratios of 10 endogenous secretion markers measured in paired urine and plasma samples at baseline. Outcome: The primary outcome was longitudinal change in eGFR. Secondary outcomes included chronic kidney disease (CKD) progression (≥50% eGFR decline or incident kidney failure requiring dialysis or kidney transplantation), a cardiovascular disease (CVD) composite (myocardial infarction, acute coronary syndrome, stroke, acute decompensated heart failure, or death from cardiovascular causes), and mortality. Analytical Approach: Linear mixed-effect models were used to evaluate the association between the secretion score and change in eGFR, and Cox proportional hazards models were used to evaluate associations with CKD progression, CVD, and mortality. Results: At baseline, mean age was 73 ± 9 years and eGFR was 46 ± 11 mL/min/1.73 m2. During a median follow-up of 3.3 years, mean change in eGFR was -1.44% per year, and 72 CKD progression events, 272 CVD events, and 144 deaths occurred. In multivariable analyses, lower secretion score was associated with faster eGFR decline and greater risk of CKD progression, CVD, and mortality. After further adjustment for baseline eGFR and albuminuria, each 1-standard deviation lower secretion score was associated with faster eGFR decline (-0.65% per year; 95% CI, -0.84% to -0.46%), but not CKD progression (HR, 1.23; 95% CI, 0.96-1.58), CVD (HR, 1.02; 95% CI, 0.89-1.18), or mortality (HR, 0.90; 95% CI, 0.74-1.09). The secretion score association with eGFR decline appeared stronger in participants with baseline eGFR <45 mL/min/1.73 m2 (P for interaction < 0.001). Limitations: Persons with diabetes and proteinuria >1 g/d were excluded. Conclusions: Among SPRINT participants with CKD, lower estimated tubular secretion was associated with faster eGFR decline, independent of baseline eGFR and albuminuria, but not with CKD progression, CVD, or mortality.

Kidney function for the non-nephrologist: an emerging tool for predicting mortality risk.

Estimated glomerular filtration rate (eGFR) and albuminuria are among the most important cardiovascular risk factors, but the optimal cutoff for predicting mortality may not yet have been agreed upon. Foley et al. analyzed data from the population-based NHANES III study with classification tree methodology. They found that an eGFR of 94 ml/min per 1.73 m(2) and an albumin-creatinine ratio of 9 mg/g were the optimal cutoff values, that is, more 'normal' values than are used to define chronic kidney disease.

Smoking is a risk factor in the progression to kidney failure.

To study the role of smoking in renal damage, we measured gender-specific effects, dose-response relationships, and whether cessation reduced the risk of smoking on future kidney failure. During a median follow-up of 10.3 years, 124 of 65,589 participants of the HUNT II study, a Norwegian population, progressed to stage 5 chronic kidney disease. Former- and current-smokers less than 70 years of age at inclusion had significant multi-adjusted hazard ratios of 3.32 and 4.01 for kidney failure compared to those who never smoked. In men, the risk increased with a significantly higher trend for cumulative smoking (pack-years); however, the risk significantly decreased with increased elapsed years since smoking cessation. Although the prevalence of current smoking did not differ between genders, females had smoked less (10.2 compared to 15.8 pack-years) and the number of kidney failure cases was lower in females than in men (46 compared to 78). The effect of smoking on the risk of kidney failure was similar (hazard ratios of 2.94 and 4.30 in current-smoking women and men, respectively), but did not reach statistical significance in women. Thus, in this large population-based sample, we found that smoking is a significant risk factor for future kidney failure. Smoking cessation decreased this risk, at least in men.

Intrauterine growth restriction: no unifying risk factor for the metabolic syndrome in young adults.

BACKGROUND: The validity and appropriateness of the metabolic syndrome as a cardiovascular risk factor are increasingly debated, partly because of the lack of a unifying underlying pathophysiological mechanism. Intrauterine growth retardation (low birth weight by sex and gestational length) has been associated with several cardiovascular problems and could be an important underlying risk factor for the metabolic syndrome. METHODS: The association between intrauterine growth retardation (from the Norwegian Medical Birth Registry) and the metabolic syndrome in 7435 men and women aged 20-30 years from the population-based HUNT 2 study was studied with logistic regression using fractional polynomial models. RESULTS: In men, there were significant associations with several of the separate components of the metabolic syndrome: central obesity (exponential, P<0.001), raised triglycerides (negative linear, P = 0.018), reduced HDL-cholesterol (U-shaped, P = 0.086), raised blood pressure (negative linear, P = 0.036), and impaired glucose tolerance (negative linear, P = 0.036). In women, there were significant associations with central obesity (positive linear, P<0.001) and raised blood pressure (negative linear, P = 0.003) but not with the other components. When combining these components into the metabolic syndrome, an exponential association was found in men (P = 0.017), that is, increased risk in patients with high birth weight only. In women, there was no association at all (P = 0.959). CONCLUSION: Low birth weight was not associated with the metabolic syndrome at young adult age. Several associations between birth weight and the separate components of the syndrome were found, however, but these associations were partly in different directions.

Screening for chronic kidney disease: which strategy?

INTRODUCTION: Screening for chronic kidney disease (CKD) has been increasingly advocated. However, several criticisms have been levied, and screening programs for CKD are not universally accepted. METHODS AND RESULTS: We discuss the problems of CKD screening and suggest improvements in the diagnostic and therapeutic strategies. Current problems with CKD screening are related to the need for both more efficient screening strategies and better screening tests. Diabetes mellitus, hypertension and age above 60 years seem to be the most important inclusion criteria for a CKD screening program, but only a small and variable proportion of CKD cases detected progress to end-stage renal disease (ESRD). Recent studies suggest that all stages of CKD should be stratified by the presence or absence of albuminuria. This applies particularly to CKD stage 3 in which a large proportion of subjects do not progress any quicker than those without kidney disease. Reduced kidney function and albuminuria are also strong and independent predictors for cardiovascular events. Screening for CKD using existing laboratory databases combined with automated management and referral recommendations based on the available evidence base seems to be a promising strategy for efficient and more adequate handling of the large number of CKD patients. CONCLUSION: Screening for CKD in the general population is still not recommended. However, high-risk groups like patients with diabetes mellitus or hypertension and subjects above age 60 should have their glomerular filtration rate estimated and be tested for albuminuria. Better interplay between primary and secondary care is needed for successful implementation of CKD clinical guidelines in general practice.

The primary care physician: nephrology interface for the identification and treatment of chronic kidney disease.

This article explores ways in which early identification of chronic kidney disease (CKD) and promotion of the concept of CKD as a modifiable risk can be achieved through transcending traditional primary and secondary care boundaries. National and regional strategies aimed at early identification of CKD in the community are reviewed, together with those aimed at implementation of management to reduce the risk both of progression of CKD and of complications.

Combining GFR and albuminuria to classify CKD improves prediction of ESRD.

Despite the high prevalence of chronic kidney disease (CKD), relatively few individuals with CKD progress to ESRD. A better understanding of the risk factors for progression could improve the classification system of CKD and strategies for screening. We analyzed data from 65,589 adults who participated in the Nord-Trøndelag Health (HUNT 2) Study (1995 to 1997) and found 124 patients who progressed to ESRD after 10.3 yr of follow-up. In multivariable survival analysis, estimated GFR (eGFR) and albuminuria were independently and strongly associated with progression to ESRD: Hazard ratios for eGFR 45 to 59, 30 to 44, and 15 to 29 ml/min per 1.73 m(2) were 6.7, 18.8, and 65.7, respectively (P < 0.001 for all), and for micro- and macroalbuminuria were 13.0 and 47.2 (P < 0.001 for both). Hypertension, diabetes, male gender, smoking, depression, obesity, cardiovascular disease, dyslipidemia, physical activity and education did not add predictive information. Time-dependent receiver operating characteristic analyses showed that considering both the urinary albumin/creatinine ratio and eGFR substantially improved diagnostic accuracy. Referral based on current stages 3 to 4 CKD (eGFR 15 to 59 ml/min per 1.73 m(2)) would include 4.7% of the general population and identify 69.4% of all individuals progressing to ESRD. Referral based on our classification system would include 1.4% of the general population without losing predictive power (i.e., it would detect 65.6% of all individuals progressing to ESRD). In conclusion, all levels of reduced eGFR should be complemented by quantification of urinary albumin to predict optimally progression to ESRD.