Cystatin C- and Creatinine-based Estimated GFR Differences: Prevalence and Predictors in the UK Biobank

Rationale & Objective

Large differences between estimated glomerular filtration rate (eGFR) based on cystatin C (eGFRcys) and creatinine (eGFRcr) occur commonly. A comprehensive evaluation of factors that contribute to these differences is needed to guide the interpretation of discrepant eGFR values.

Study Design

Cohort study.

Setting & Participants

468,969 participants in the UK Biobank.

Exposures

Candidate sociodemographic, lifestyle factors, comorbidities, medication usage, and physical and laboratory predictors.

Outcomes

eGFRdiff, defined as eGFRcys minus eGFRcr, categorized into 3 levels: lower eGFRcys (eGFRdiff, less than -15 mL/min/1.73 m2), concordant eGFRcys and eGFRcr (eGFRdiff, -15 to < 15 mL/min/1.73 m2), and lower eGFRcr (eGFRdiff, ≥15 mL/min/1.73 m2).

Analytical Approach

Multinomial logistic regression models were constructed to identify predictors of lower eGFRcys or lower eGFRcr. We developed 2 prediction models comprising 375,175 participants: (1) a clinical model using clinically available variables and (2) an enriched model additionally including lifestyle variables. The models were internally validated in an additional 93,794 participants.

Results

Mean ± standard deviation of eGFRcys was 88 ± 16 mL/min/1.73 m2, and eGFRcr was 95 ± 13 mL/min/1.73 m2; 25% and 5% of participants were in the lower eGFRcys and lower eGFRcr groups, respectively. In the multivariable enriched model, strong predictors of lower eGFRcys were older age, male sex, South Asian ethnicity, current smoker (vs never smoker), history of thyroid dysfunction, chronic inflammatory disease, steroid use, higher waist circumference and body fat, and urinary albumin-creatinine ratio >300 mg/g. Odds ratio estimates for these predictors were largely inverse of those in the lower eGFRcr group. The model's area under the curve was 0.75 in the validation set, with good calibration (1.00).

Limitations

Limited generalizability.

Conclusions

This study highlights the multitude of demographic, lifestyle, and health characteristics that are associated with large eGFRdiff. The clinical model may identify individuals who are likely to have discrepant eGFR values and thus should be prioritized for cystatin C testing.

Decision-Making Engagement Preferences among Older Adults with CKD

Key Points

Background

Older adults with kidney failure face preference-sensitive decisions regarding dialysis initiation. Despite recommendations, few older patients with kidney failure experience shared decision making. Clinician uncertainty about the degree to which older patients prefer to engage in decision making remains a key barrier.

Methods

This study follows a mixed-methods explanatory, longitudinal, sequential design at four diverse US centers with patients (English-fluent, aged ≥70 years, CKD stages 4–5, nondialysis) from 2018 to 2020. Patient preferences for engagement in decision making were assessed using the Control Preferences Scale, reflecting the degree to which patients want to be involved in their decision making: active (the patient prefers to make the final decision), collaborative (the patient wants to share decision making with the clinician), or passive (the patient wants the clinician to make the final decision) roles. Semistructured interviews about engagement and decision making were conducted in two waves (2019, 2020) with purposively sampled patients and clinicians. Descriptive statistics and ANOVA were used for quantitative analyses; thematic and narrative analyses were used for qualitative data.

Results

Among 363 patient participants, mean age was 78±6 years, 42% were female, and 21% had a high school education or less. Control Preferences Scale responses reflected that patients preferred to engage actively (48%) or collaboratively (43%) versus passively (8%). Preferred roles remained stable at 3-month follow-up. Seventy-six participants completed interviews (45 patients, 31 clinicians). Four themes emerged: control preference roles reflect levels of decisional engagement; clinicians control information flow, especially about prognosis; adapting a clinical approach to patient preferred roles; and clinicians' responsiveness to patient preferred roles supports patients' satisfaction with shared decision making.

Conclusions

Most older adults with advanced CKD preferred a collaborative or active role in decision making. Appropriately matched information flow with patient preferences was critical for satisfaction with shared decision making.

Clinical Trial registry name and registration number:

Decision Aid for Renal Therapy (DART), NCT03522740.

Tubule dysfunction and injury and future risk of sepsis-associated acute kidney injury

BACKGROUND

Novel biomarkers can quantify both kidney tubule function, including proximal tubule reabsorptive (urine α-1 microglobulin (uα1m)) and tubule protein synthesis capacities (urine uromodulin (uUMOD)), and tubular injury (urine neutrophil gelatinase-associated lipocalin (uNGAL)). In a blood pressure trial, we reported that lower reabsorptive and synthetic protein capacity at times of health predicted future risk of acute kidney injury (AKI), but most AKI was related to hemodynamic causes in this trial. Associations between tubular function and injury and future AKI related to other causes is unknown.

MATERIALS AND METHODS

We performed a case-control study in REGARDS, a population-based cohort study, among participants who provided urine at the baseline visit. We matched each septic AKI case by age, sex, race, and time from baseline to hospital admission 1 : 1 to a participant with sepsis who did not develop AKI (controls). Using conditional logistic regression, we evaluated the associations of uα1m, uUMOD, urine ammonium, and uNGAL with septic AKI.

RESULTS

Mean age was 69 ± 8 years, 44% were female, and 39% were Black participants. Median baseline eGFR among cases and controls was 73 (55, 90) and 82 (65, 92) mL/min/1.73m2, and median albuminuria was 19 (8, 87) vs. 9 (5, 22) mg/g, respectively. No independent associations were observed between the tubule function or injury markers and subsequent risk of septic AKI once models were adjusted for baseline albuminuria, estimated glomerular filtration rate, and other risk factors.

CONCLUSION

Among community participants, tubule function and injury markers at times of health were not independently associated with future risk of septic AKI.

Plasma proenkephalin A and incident chronic kidney disease and albuminuria in the REasons for Geographic And Racial Differences in Stroke (REGARDS) cohort

BACKGROUND

Plasma proenkephalin A (PENK-A) is a precursor of active enkephalins. Higher blood concentrations have been associated with estimated glomerular filtration rate (eGFR) decline in European populations. Due to the significant disparity in incident chronic kidney disease (CKD) between White and Black people, we evaluated the association of PENK-A with incident CKD and other kidney outcomes among a biracial cohort in the U.S.

METHODS

In a nested cohort of 4,400 participants among the REasons for Geographic And Racial Differences in Stroke, we determined the association between baseline PENK-A concentration and incident CKD using the creatinine-cystatin C CKD-EPI 2021 equation without race coefficient, significant eGFR decline, and incident albuminuria between baseline and a follow-up visit 9.4 years later. We tested for race and sex interactions. We used inverse probability sampling weights to account for the sampling design.

RESULTS

At baseline, mean (SD) age was 64 (8) years, 49% were women, and 52% were Black participants. 8.5% developed CKD, 21% experienced ≥ 30% decline in eGFR and 18% developed albuminuria. There was no association between PENK-A and incident CKD and no difference by race or sex. However, higher PENK-A was associated with increased odds of progressive eGFR decline (OR: 1.12; 95% CI 1.00, 1.25). Higher PENK-A concentration was strongly associated with incident albuminuria among patients without diabetes mellitus (OR: 1.29; 95% CI 1.09, 1.53).

CONCLUSION

While PENK-A was not associated with incident CKD, its associations with progression of CKD and incident albuminuria, among patients without diabetes, suggest that it might be a useful tool in the evaluation of kidney disease among White and Black patients.

Lost in Translation: Why Are Rates of Hypertension Control Getting Worse Over Time?

Treatment of hypertension to decrease rates of cardiovascular disease is the most well studied and most broadly applicable treatment in cardiovascular prevention. Blood pressure can be measured anywhere, not just in a physician's office; medications are readily available, inexpensive, and have highly favorable benefit/harm ratios with relatively minimal side effects; and stepped medication regimens can be prescribed in algorithmic fashion by a variety of practitioners. Yet overall hypertension control rates in the United States have never exceeded 60%, and the last 5-10 years have seen decreased, rather than increased, rates of control. Here, I describe the scale of this massive failure to deliver on the promise of preventive hypertension care; outline the populations most affected and the contemporaneous events that have impacted hypertension control; discuss the disparate paths of hypertension science and health care delivery; and highlight novel interventions, approaches, and future opportunities to bend the curve back toward improvements in hypertension control.

Urine Uromodulin, Kidney Tubulointerstitial Fibrosis, and Furosemide Response

BACKGROUND

Interstitial fibrosis and tubular atrophy (IFTA) are common findings on biopsy in chronic kidney disease (CKD) and strongly predictive of kidney failure. IFTA is poorly correlated with estimated glomerular filtration rate (eGFR) and albuminuria, the most common metrics of kidney disease. Thus, IFTA is prognostically important, yet its presence and severity are invisible to the clinician except when kidney biopsies are obtained.

OBJECTIVES

To investigate 1) the cross-sectional association between urine uromodulin (uUMOD) and IFTA, and 2) to determine whether uUMOD levels were associated with diuretic response after a furosemide stress test.

METHODS

We performed logistic regression to evaluate the association between uUMOD and fibrosis. We used linear regression models to assess the association of uUMOD with urine output.

RESULTS

Among 52 participants, the mean age was 42 ± 16 years, 48% were women, 23% had diabetes, and the median eGFR was 56 ml/min/1.73m2. The mean uUMOD concentration was 5.1 (8.4) mcg/mL. Each halving of uUMOD was associated with 1.74 higher odds (95% CI 1.10, 2.75) of grade 2 or 3 fibrosis. However, this association was no longer significant after adjusting for baseline eGFR and albuminuria. Each halving of urine uromodulin was associated with a decreased response to furosemide. This association was also no longer significant after adjusting for baseline eGFR and albuminuria.

CONCLUSION

In a population of individuals with a wide range of kidney function undergoing clinically indicated kidney biopsies, we did not find an association between uUMOD and interstitial fibrosis or response to loop diuretics after adjusting for eGFR and albuminuria.

Markers of Kidney Tubule Dysfunction and Major Adverse Kidney Events

BACKGROUND

Serum creatinine and albuminuria are primary markers of glomerular function and injury, respectively. Tubular secretion, acid-base homeostasis, protein reabsorption, among other tubular functions, are largely ignored. This mini-review aimed to discuss how two tubular functions, secretion, and acid-base homeostasis are associated with major adverse kidney events (MAKEs).

SUMMARY

Proximal tubular secretion is an essential function that allows the elimination of endogenous substances and drugs. Recently discovered endogenous markers in urine and plasma allow a noninvasive way of assessing tubular secretion markers. Several studies have found an association between these markers and a higher risk of chronic kidney disease (CKD) progression and mortality. In a study we recently performed among patients with CKD and at risk of cardiovascular events, lower tubular secretion was associated with an increased risk of acute kidney injury and metabolic acidosis, independent of baseline eGFR and albuminuria. The kidney tubules also play a crucial role in acid-base homeostasis. Although the standard clinical assessment of acidosis consists of measuring serum bicarbonate, urinary ammonium excretion decreases before over metabolic acidosis. Urinary ammonium excretion is associated with CKD progression, a higher risk of kidney failure, and an increased mortality risk, independent of baseline eGFR and albuminuria.

KEY MESSAGES

Novel biomarkers of kidney tubular health consistently associate with MAKEs, above and beyond baseline eGFR, albuminuria, and other CKD risk factors. Tubular markers may provide new opportunities to improve kidney prognosis, drug dosing, and monitoring for adverse events.

Association of Intra-individual Differences in Estimated GFR by Creatinine Versus Cystatin C With Incident Heart Failure

RATIONALE & OBJECTIVE

Lower estimated glomerular filtration rate (eGFR) is associated with heart failure (HF) risk. However, eGFR based on cystatin C (eGFRcys) and creatinine (eGFRcr) may differ substantially within an individual. The clinical implications of these differences for risk of HF among persons with chronic kidney disease (CKD) are unknown.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

4,512 adults with CKD and without prevalent HF who enrolled in the Chronic Renal Insufficiency Cohort (CRIC) Study.

EXPOSURE

Difference in GFR estimates (eGFRdiff; ie, eGFRcys minus eGFRcr).

OUTCOME

Incident HF hospitalization.

ANALYTICAL APPROACH

Fine-Gray proportional subhazards regression was used to investigate the associations of baseline, time-updated, and slope of eGFRdiff with incident HF.

RESULTS

Of 4,512 participants, one-third had eGFRcys and eGFRcr values that differed by over 15 mL/min/1.73 m2. In multivariable-adjusted models, each 15 mL/min/1.73 m2 lower baseline eGFRdiff was associated with higher risk of incident HF hospitalization (hazard ratio [HR], 1.20 [95% CI, 1.07-1.34]). In time-updated analyses, those with eGFRdiff less than -15 mL/min/1.73 m2 had higher risk of incident HF hospitalization (HR, 1.99 [95% CI, 1.39-2.86]), and those with eGFRdiff ≥15 mL/min/1.73 m2 had lower risk of incident HF hospitalization (HR, 0.67 [95% CI, 0.49-0.91]) compared with participants with similar eGFRcys and eGFRcr. Participants with faster declines in eGFRcys relative to eGFRcr had higher risk of incident HF (HR, 1.49 [95% CI, 1.19-1.85]) compared with those in whom eGFRcys and eGFRcr declined in parallel.

LIMITATIONS

Entry into the CRIC Study was determined by eGFRcr, which constrained the range of baseline eGFRcr-but not eGFRcys-values.

CONCLUSIONS

Among persons with CKD who have large differences between eGFRcys and eGFRcr, risk for incident HF is more strongly associated with eGFRcys. Diverging slopes between eGFRcys and eGFRcr over time are also independently associated with risk of incident HF.

Relationship of Kidney Tubule Biomarkers with Cognition among Community-Living Elders in the Health ABC Study

Higher baseline urinary neutrophil gelatinase-associated lipocalin was associated with worse cognitive scores at baseline.Lower concentrations of baseline serum bicarbonate (higher is better) were associated with lower cognitive scores at baseline.We found no associations with urine markers with longitudinal changes in cognition.

Marathon Runners' Knowledge and Strategies for Hydration

OBJECTIVE

To study hydration plans and understanding of exercise-associated hyponatremia (EAH) among current marathon runners.

DESIGN

Cross-sectional study.

SETTING

Southern California 2018 summer marathon.

PARTICIPANTS

Two hundred ten marathon runners.

INTERVENTIONS

Survey administered 1 to 2 days before the race. Race times were obtained from public race website.

MAIN OUTCOME MEASURES

Planned frequency of hydration; awareness of, understanding of, and preventative strategies for dehydration and EAH; resources used to create hydration plans; drink preferences.

RESULTS

When the participants were split into 3 equal groups by racing speed, the slower tertile intended to drink at every mile/station (60%), whereas the faster tertile preferred to drink every other mile or less often (60%), although not statistically significant. Most runners (84%) claimed awareness of EAH, but only 32% could list a symptom of the condition. Both experienced marathoners and the faster tertile significantly had greater understanding of hyponatremia compared with first-time marathoners and the slower tertile, respectively. Less than 5% of marathoners offered "drink to thirst" as a prevention strategy for dehydration or EAH.

CONCLUSION

Slower runners plan to drink larger volumes compared with their faster counterparts. Both slower and first-time marathoners significantly lacked understanding of EAH. These groups have plans and knowledge that may put them at higher risk for developing EAH. Most marathon runners did not know of the guidelines to "drink to thirst," suggesting the 2015 EAH Consensus statement may not have had the desired impact.

Treatment Decision Making for Older Kidney Patients during COVID-19

BACKGROUND AND OBJECTIVES

Coronavirus disease 2019 (COVID-19) disrupted medical care across health care settings for older patients with advanced CKD. Understanding how shared decision making for kidney treatment decisions was influenced by the uncertainty of an evolving pandemic can provide insights for supporting shared decision making through the current and future public health crises.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed thematic and narrative analyses of semistructured interviews with patients (CKD stages 4 and 5, age 70+), care partners, and clinicians from Boston, Portland (Maine), San Diego, and Chicago from August to December 2020.

RESULTS

We interviewed 76 participants (39 patients, 17 care partners, and 20 clinicians). Among patient participants, 13 (33%) patients identified as Black, and seven (18%) had initiated dialysis. Four themes with corresponding subthemes emerged related to treatment decision making and the COVID-19 pandemic: (1) adapting to changed educational and patient engagement practices (patient barriers to care and new opportunities for telemedicine); (2) reconceptualizing vulnerability (clinician awareness of illness severity increased and limited discussions of patient COVID-19 vulnerability); (3) embracing home-based dialysis but not conservative management (openness to home-based modalities and limited discussion of conservative management and advanced care planning); and (4) satisfaction and safety with treatment decisions despite conditions of uncertainty.

CONCLUSIONS

Although clinicians perceived greater vulnerability among older patients CKD and more readily encouraged home-based modalities during the COVID-19 pandemic, their discussions of vulnerability, advance care planning, and conservative management remained limited, suggesting areas for improvement. Clinicians reported burnout caused by the pandemic, increased time demands, and workforce limitations, whereas patients remained satisfied with their treatment choices despite uncertainty.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Decision Aid for Renal Therapy (DART), NCT03522740.

Association of Intraindividual Difference in Estimated Glomerular Filtration Rate by Creatinine vs Cystatin C and End-stage Kidney Disease and Mortality

Importance

As cystatin C is increasingly adopted to estimate glomerular filtration rate (eGFR), clinicians will encounter patients in whom cystatin C-based eGFR (eGFRcys) and creatinine-based eGFR (eGFRcr) differ widely. The clinical implications of these differences, eGFRdiffcys-cr, are unknown.

Objective

To evaluate the associations of eGFRdiffcys-cr with end-stage kidney disease (ESKD) and mortality among individuals with chronic kidney disease (CKD).

Design, Setting, and Participants

This is a prospective cohort study of 4956 individuals with mild to moderate CKD from 7 clinical centers in the United States who enrolled in the Chronic Renal Insufficiency Cohort (CRIC) Study between 2003 to 2018. Statistical analyses were completed in December 2021.

Exposures

eGFRdiffcys-cr (eGFRcys - eGFRcr) was calculated at baseline and annually thereafter for 3 years. Because 15 mL/min/1.73 m2 represents a clinically meaningful difference in eGFR that also distinguishes CKD stages, eGFRdiffcys-cr was categorized as: less than -15 mL/min/1.73 m2, -15 to 15 mL/min/1.73 m2, and 15 mL/min/1.73 m2 or greater.

Main Outcomes and Measures

The outcomes of ESKD, defined as initiation of maintenance dialysis or receipt of a kidney transplant, and all-cause mortality were adjudicated from study entry until administrative censoring in 2018.

Results

Among 4956 participants with mean (SD) age of 59.5 (10.5) years, 2152 (43.4%) were Black, 515 (10.4%) were Hispanic, and 2113 (42.6%) were White. There were 2156 (43.5%) women and 2800 (56.5%) men. At baseline, eGFRcys and eGFRcr values differed by more than 15 mL/min/1.73 m2 in one-third of participants (1638 participants [33.1%]). Compared with participants with similar baseline eGFRcys and eGFRcr (eGFRdiffcys-cr -15 to 15 mL/min/1.73 m2), those in whom eGFRcys was substantially lower than eGFRcr (eGFRdiffcys-cr < -15 mL/min/1.73 m2) had a higher risk of mortality (hazard ratio [HR], 1.86; 95% CI, 1.40-2.48) while those with eGFRdiffcys-cr of 15 mL/min/1.73 m2 or greater had lower risks of ESKD (subHR [SHR], 0.73; 95% CI, 0.59-0.89) and mortality (HR, 0.68; 95% CI, CI 0.58-0.81). In time-updated analyses, participants with eGFRdiffcys-cr less than -15 mL/min/1.73 m2 had higher risks of ESKD (SHR, 1.83; 95% CI, 1.10-3.04) and mortality (HR, 3.03; 95% CI, 2.19-4.19) compared with participants with similar eGFRcys and eGFRcr. Conversely, participants with eGFRdiffcys-cr of 15 mL/min/1.73 m2 or greater had lower risks of ESKD (SHR, 0.50; 95% CI, 0.35-0.71) and mortality (HR, 0.58; 95% CI, 0.45-0.75). Longitudinal changes in eGFRdiffcys-cr were associated with mortality risk. Compared with participants who had similar slopes by eGFRcys and eGFRcr, those with smaller eGFRcr declines had an 8-fold increased mortality risk (HR, 8.20; 95% CI, 6.37-10.56), and those with larger apparent declines by eGFRcr had a lower mortality risk (HR, 0.14; 95% CI, 0.08-0.24).

Conclusions and Relevance

These findings suggest that large differences between eGFRcys and eGFRcr were common in persons with CKD. These differences and their changes over time may be informative of ESKD and mortality risks, warranting monitoring of both eGFRcys and eGFRcr in this high-risk population.

Cystatin C and Creatinine-Based Glomerular Filtration Rate Estimation Differences and Muscle Quantity and Functional Status in Older Adults

Rationale & Objective

The difference in the estimated glomerular filtration rate based on cystatin C and that based on creatinine (eGFRDiff) is known to be associated with frailty and mortality. Creatinine is influenced by muscle mass, more so than cystatin C; we aimed to determine whether eGFRDiff is associated with muscle quantity and to what extent muscle quantity explains the relationship between eGFRDiff and poor functional status.

Study Design

A cohort analysis of the health, aging, and body composition study (HABC).

Setting & Participants

Overall, 2,970 HABC participants had their baseline serum creatinine level, cystatin C level, and body composition measured using imaging.

Exposure

Estimated glomerular filtration rates (eGFRs) were calculated using Chronic Kidney Disease Epidemiology Collaboration equations (estimated glomerular filtration rate based on cystatin C [eGFR_Cys] and estimated glomerular filtration rate based on creatinine [eGFR_Cr]), and eGFRDiff was calculated as eGFR_Cys − eGFR_Cr.

Outcomes

The total thigh muscle area was evaluated using computed tomography. The health, aging, and body composition study physical performance battery was scored on a continuous scale (standing and walking tasks); poor functional status was characterized by the lowest quartile.

Analytical Approach

We used linear regression to model the cross-sectional association of eGFRDiff and muscle measures. We used logistic regression to evaluate the association of eGFRDiff with poor functional status.

Results

The mean age was 74 ± 3 years; the eGFR_Cys, eGFR_Cr, and eGFRDiff was 72 ± 18, 68 ± 15, and 4 ± 14 mL/min/1.73 m², respectively. Compared with participants in the reference group (−10 < eGFRDiff ≤ 10 mL/min/1.73 m²), those in the negative eGFRDiff group (≤−10 mL/min/1.73 m²) were more likely to have comorbidities, a slower gait, and worse functional status. They had an approximately 14-cm² smaller thigh muscle area in a fully adjusted model. Compared with the reference group, those in the negative group had 1.89-fold higher odds of poor functional status (unadjusted). This relationship was minimally attenuated after adjustment for thigh muscle, thigh fat area, appendicular lean mass, and limb fat mass, both individually and in combination.

Limitations

The functional status outcome was specific to HABC. The muscle measures did not capture dynamic turnover.

Conclusions

The difference of eGFR_Cys − eGFR_Cr provides information on older adults’ functional status, which is only partially explained by muscle quantity and quality.

Patient Education for Kidney Failure Treatment: A Mixed-Methods Study

RATIONALE & OBJECTIVE

Education programs are needed for people with advanced chronic kidney disease to understand kidney failure treatment options and participate in shared decision-making (SDM). Little is known about the content and accessibility of current education programs or whether they support SDM.

STUDY DESIGN

Stakeholder-engaged, mixed-methods design incorporating qualitative observations and interviews, and a quantitative content analysis of slide presentations.

SETTING & PARTICIPANTS

Four sites located in Boston, Chicago, Portland (Maine), and San Diego.

ANALYTICAL APPROACH

Thematic analysis based on the Ottawa Framework (observations and interviews) and descriptive statistical analysis (slide presentations).

RESULTS

Data were collected from observations of 9 education sessions, 5 semistructured interviews with educators, and 133 educational slide presentations. Sites offered group classes or one-on-one sessions. Development, quality, and accuracy of educational materials varied widely. Educators emphasized dialysis (often in-center hemodialysis), with little mention of conservative management. Educators reported patients were often referred too late to education sessions and that some patients become overwhelmed if they learn of the implications of kidney failure in a group setting. Commonly, sessions were general and did not provide opportunities for tailored information most supportive of SDM. Few nephrologists were involved in education sessions or aware of the educational content. Content gaps included prognosis, decision support, mental health and cognition, advance care planning, cost, and diet. Slide presentations used did not consistently reflect best practices related to health literacy.

LIMITATIONS

Findings may not be broadly generalizable.

CONCLUSIONS

Education sessions focused on kidney failure treatment options do not consistently follow best practices related to health literacy or for supporting SDM. To facilitate SDM, the establishment of expectations for kidney failure treatment options should be clearly defined and integrated into the clinical workflow. Addressing content gaps, health literacy, and communication with nephrologists is necessary to improve patient education in the setting of advanced chronic kidney disease.

The Relationship Between Urine Uromodulin and Blood Pressure Changes: The DASH-Sodium Trial

BACKGROUND

Uromodulin modulates the sodium-potassium-two-chloride transporter in the thick ascending limb of the loop of Henle, and its overexpression in murine models leads to salt-induced hypertension. We hypothesized that individuals with higher baseline levels of urine uromodulin would have a greater increase in systolic blood pressure (SBP) for the same increase in sodium compared with those with lower uromodulin levels.

METHODS

We used data from 157 subjects randomized to the control diet of the Dietary Approaches to Stop Hypertension (DASH)-Sodium trial who were assigned to 30 days of low (1,500 mg/d), medium (2,400 mg/d), and high salt (3,300 mg/d) diets in random order. Blood pressure was measured prerandomization and then weekly during each feeding period. We evaluated the association of prerandomization urine uromodulin with change in SBP between diets, as measured at the end of each feeding period, using multivariable linear regression.

RESULTS

Baseline urine uromodulin stratified by tertiles was ≤17.64, 17.65-31.97, and ≥31.98 µg/ml. Across the tertiles, there were no significant differences in SBP at baseline, nor was there a differential effect of sodium diet on SBP across tertiles (low to high, P = 0.81). After adjusting for age, sex, body mass index, and race, uromodulin levels were not significantly associated with SBP change from low to high sodium diet (P = 0.42).

CONCLUSIONS

In a randomized trial of different levels of salt intake, higher urine uromodulin levels were not associated with a greater increase in blood pressure in response to high salt intake.

The Difference Between Cystatin C- and Creatinine-Based Estimated GFR and Associations With Frailty and Adverse Outcomes: A Cohort Analysis of the Systolic Blood Pressure Intervention Trial (SPRINT)

RATIONALE & OBJECTIVE

In prior research and in practice, the difference between estimated glomerular filtration rate (eGFR) calculated from cystatin C level and eGFR calculated from creatinine level has not been assessed for clinical significance and relevance. We evaluated whether these differences contain important information about frailty.

STUDY DESIGN

A cohort analysis of the Systolic Blood Pressure Intervention Trial (SPRINT).

SETTING & PARTICIPANTS

9,092 hypertensive SPRINT participants who had baseline measurements of serum creatinine, cystatin C, and frailty.

EXPOSURE

eGFRs calculated using CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equations (eGFR_cys and eGFR_cr), and eGFR_Diff, calculated as eGFR_cys-eGFR_cr.

OUTCOMES

A validated 35-item frailty index that included questionnaire data for general and physical health, limitations of activities, pain, depression, sleep, energy level, self-care, and smoking status, as well as medical history, cognitive assessment, and laboratory data. We defined frailty as frailty index score>0.21 (range, 0-1). The incidence of injurious falls, hospitalizations, cardiovascular events, and mortality was also recorded.

ANALYTICAL APPROACH

We used logistic regression to model the cross-sectional association of baseline eGFR_Diff with frailty among all SPRINT participants. Adjusted proportional hazards regression was used to evaluate the association of eGFR_Diff with adverse outcomes and mortality.

RESULTS

Mean age was 68±9 (SD) years, mean eGFR_cys and eGFR_cr were 73±23 and 72±20mL/min/1.73m², and mean eGFR_Diff was 0.5±15mL/min/1.73m². In adjusted models, each 1-SD higher eGFR_Diff was associated with 24% lower odds of prevalent frailty (OR, 0.76; 95% CI, 0.71-0.81), as well as with lower incidence rate of injurious falls (HR, 0.84; 95% CI, 0.77-0.92), hospitalization (HR, 0.91; 95% CI, 0.88-0.95), cardiovascular events (HR, 0.89; 95% CI, 0.81-0.97), and all-cause mortality (HR, 0.71; 95% CI, 0.63-0.82); P<0.01.

LIMITATIONS

Gold-standard measure of kidney function and assessment of muscle mass were not available.

CONCLUSIONS

The difference between eGFR_cys and eGFR_cr is associated with frailty and health status. Positive eGFR_Diff is strongly associated with lower risks for longitudinal adverse outcomes and mortality, even after adjusting for chronic kidney disease stage and baseline frailty.

Kidney Disease, Intensive Hypertension Treatment, and Risk for Dementia and Mild Cognitive Impairment: The Systolic Blood Pressure Intervention Trial

BACKGROUND

Intensively treating hypertension may benefit cardiovascular disease and cognitive function, but at the short-term expense of reduced kidney function.

METHODS

We investigated markers of kidney function and the effect of intensive hypertension treatment on incidence of dementia and mild cognitive impairment (MCI) in 9361 participants in the randomized Systolic Blood Pressure Intervention Trial, which compared intensive versus standard systolic BP lowering (targeting <120 mm Hg versus <140 mm Hg, respectively). We categorized participants according to baseline and longitudinal changes in eGFR and urinary albumin-to-creatinine ratio. Primary outcomes were occurrence of adjudicated probable dementia and MCI.

RESULTS

Among 8563 participants who completed at least one cognitive assessment during follow-up (median 5.1 years), probable dementia occurred in 325 (3.8%) and MCI in 640 (7.6%) participants. In multivariable adjusted analyses, there was no significant association between baseline eGFR <60 ml/min per 1.73 m² and risk for dementia or MCI. In time-varying analyses, eGFR decline ≥30% was associated with a higher risk for probable dementia. Incident eGFR <60 ml/min per 1.73 m² was associated with a higher risk for MCI and a composite of dementia or MCI. Although these kidney events occurred more frequently in the intensive treatment group, there was no evidence that they modified or attenuated the effect of intensive treatment on dementia and MCI incidence. Baseline and incident urinary ACR ≥30 mg/g were not associated with probable dementia or MCI, nor did the urinary ACR modify the effect of intensive treatment on cognitive outcomes.

CONCLUSIONS

Among hypertensive adults, declining kidney function measured by eGFR is associated with increased risk for probable dementia and MCI, independent of the intensity of hypertension treatment.

Relation of Plasma Renin Activity to Subclinical Peripheral and Coronary Artery Disease (from the Multiethnic Study of Atherosclerosis)

Experimental studies support a link between activation of the renin-angiotensin-aldosterone system and cardiovascular disease (CVD). The relationship with subclinical atherosclerosis is uncertain. Among 1,699 individuals without prevalent CVD from the Multiethnic Study of Atherosclerosis, we measured plasma renin activity (PRA) and aldosterone. Using multivariable logistic regression with restricted cubic splines, we assessed continuous log-transformed PRA and aldosterone associations with the ankle-brachial index (ABI) and coronary artery calcium (CAC) scores (Agatston) with adjustment for cardiovascular disease (CVD) risk factors, kidney function, and inflammatory biomarkers. In fully adjusted models mutually adjusting for PRA and aldosterone, higher PRA was associated with an ABI <1.0 (p overall <0.001, p nonlinear = 0.02) and CAC Agatston score >300 (p overall = 0.02, p nonlinear = 0.22), while aldosterone was not associated with either outcome. For example, compared to the 10th percentile (0.16 ng/ml/hr) of PRA, the 90th percentile (2.68 ng/ml/hr) had 3.6 times (OR 3.62; 95% CI: 2.13 to 6.13) and 1.7 times higher odds (odds ratio 1.67; 95% confidence interval: 1.13 to 2.48) of ABI <1.0 and CAC >300, respectively. These associations persisted after adjustment for levels of C-reactive protein, Interleukin-6, and Tumor Necrosis Factor-alpha. There were no significant differences in these associations by race/ethnicity or antihypertensive medication status. In conclusion, in a multiethnic cohort of community-living adults without prevalent clinical CVD, PRA was associated with greater burden of subclinical peripheral artery and coronary artery disease. These findings provide additional evidence that PRA may have deleterious effects on cardiovascular health through an atherosclerotic pathway.

Serum Bicarbonate as a Surrogate for pH in Hemodialysis: A Pilot Study

Rationale & Objective

Excess morbidity and mortality are associated with both high and low serum bicarbonate levels in epidemiologic studies of patients with end-stage kidney disease (ESKD) receiving hemodialysis. The Kidney Disease Outcomes Quality Initiative (KDOQI) recommends modifying dialysate bicarbonate concentration to achieve a predialysis serum bicarbonate level ≥ 22 mmol/L, measured as total carbon dioxide (CO₂). This practice assumes that total CO₂ is an adequate surrogate for acid-base status, yet its surrogacy performance is unknown in ESKD. We determined acid-base status at the beginning and end of hemodialysis using total CO₂ and pH and tested whether total CO₂ is an appropriate surrogate for acid-base status.

Study Design

Pilot study.

Setting & Participants

25 veterans with ESKD receiving outpatient hemodialysis.

Tests Compared

pH, calculated bicarbonate level, and total CO₂.

Outcomes

The proportion of paired samples for which total CO₂ misclassified acid-base status according to pH was determined. Bias of total CO₂ was evaluated using Bland-Altman plots, comparing it to calculated bicarbonate.

Results

Among 71 samples, mean pH was 7.41 ± 0.03 predialysis and 7.48 ± 0.05 postdialysis. Compared with interpretation of full blood gas profiles, 9 of 25 (36%) participants were misclassified as acidemic using predialysis total CO₂ measures alone (total CO₂ < 22 mmol/L but pH ≥ 7.38); 1 (4%) participant was misclassified as alkalemic (total CO₂ > 26 mmol/L but pH ≤ 7.42). Among paired samples in which predialysis total CO₂ was < 22 mmol/L, the corresponding pH was acidemic (< 7.38) in just 3 of 13 (23%) instances.

Limitations

Small, single-center, entirely male cohort.

Conclusions

A majority of participants became alkalemic during routine hemodialysis despite arriving with normal pH. 10 of 25 (40%) participants' acid-base status was misclassified using total CO₂ measurements alone; the majority of predialysis total CO₂ values that would trigger therapeutic modification according to practice guidelines did not have acidemia when assessed using pH. Efforts to improve dialysis prescription require recognition that total CO₂ may not be reliable for interpreting acid-base status in hemodialysis patients.

Effect of Intensive and Standard Clinic-Based Hypertension Management on the Concordance Between Clinic and Ambulatory Blood Pressure and Blood Pressure Variability in SPRINT

Background Blood pressure ( BP ) varies over time within individual patients and across different BP measurement techniques. The effect of different BP targets on concordance between BP measurements is unknown. The goals of this analysis are to evaluate concordance between (1) clinic and ambulatory BP , (2) clinic visit-to-visit variability and ambulatory BP variability, and (3) first and second ambulatory BP and to evaluate whether different clinic targets affect these relationships. Methods and Results The SPRINT (Systolic Blood Pressure Intervention Trial) ambulatory BP monitoring ancillary study obtained ambulatory BP readings in 897 participants at the 27-month follow-up visit and obtained a second reading in 203 participants 293±84 days afterward. There was considerable lack of agreement between clinic and daytime ambulatory systolic BP with wide limits of agreement in Bland-Altman plots of -21 to 34 mm Hg in the intensive-treatment group and -26 to 32 mm Hg in the standard-treatment group. Overall, there was poor agreement between clinic visit-to-visit variability and ambulatory BP variability with correlation coefficients for systolic and diastolic BP all <0.16. We observed a high correlation between first and second ambulatory BP ; however, the limits of agreement were wide in both the intensive group (-27 to 21 mm Hg) and the standard group (-23 to 20 mm Hg). Conclusions We found low concordance in BP and BP variability between clinic and ambulatory BP and second ambulatory BP . Results did not differ by treatment arm. These results reinforce the need for multiple BP measurements before clinical decision making.

Urinary Biomarkers of Tubular Damage Are Associated with Mortality but Not Cardiovascular Risk among Systolic Blood Pressure Intervention Trial Participants with Chronic Kidney Disease

BACKGROUND

Kidney tubulointerstitial fibrosis on biopsy is a strong predictor of chronic kidney disease (CKD) progression, and CKD is associated with elevated risk of cardiovascular disease (CVD). Tubular health is poorly quantified by traditional kidney function measures, including estimated glomerular filtration rate (eGFR) and albuminuria. We hypothesized that urinary biomarkers of tubular injury, inflammation, and repair would be associated with higher risk of CVD and mortality in persons with CKD.

METHODS

We measured urinary concentrations of interleukin-18 (IL-18), kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and chitinase-3-like protein-1 (YKL-40) at baseline among 2,377 participants of the Systolic Blood Pressure Intervention Trial who had an eGFR < 60 mL/min/1.73 m2. We used Cox proportional hazards models to evaluate biomarker associations with CVD events and all-cause mortality.

RESULTS

At baseline, the mean age of participants was 72 ± 9 years, and eGFR was 48 ± 11 mL/min/1.73 m2. Over a median follow-up of 3.8 years, 305 CVD events (3.6% per year) and 233 all-cause deaths (2.6% per year) occurred. After multivariable adjustment including eGFR, albuminuria, and urinary creatinine, none of the biomarkers showed statistically significant associations with CVD risk. Urinary IL-18 (hazard ratio [HR] per 2-fold higher value, 1.14; 95% CI 1.01-1.29) and YKL-40 (HR per 2-fold higher value, 1.08; 95% CI 1.02-1.14) concentrations were each incrementally associated with higher mortality risk. Associations were similar when stratified by randomized blood pressure arm.

CONCLUSIONS

Among hypertensive trial participants with CKD, higher urinary IL-18 and YKL-40 were associated with higher risk of mortality, but not CVD.

The association of the ankle-brachial index, the toe-brachial index, and their difference, with mortality and limb outcomes in dialysis patients

INTRODUCTION

The ankle-brachial index (ABI) is the most common test to diagnose peripheral artery disease (PAD). In dialysis patients, the ABI may under-diagnose PAD, due to a high prevalence of concomitant medial arterial calcification (MAC). The toe-brachial index (TBI) is not as susceptible to misclassification by MAC. Taking the ABI and TBI together in the form of their difference, the ABI-TBI, may provide a single measure for assessing both atherosclerosis and calcification. The relationship of these variables in dialysis patients has not been well studied.

METHODS

We identified 37 dialysis patients referred for vascular studies between 2009 and 2017 in the San Diego Veterans Administration Medical Center (SDVAMC). The ABI and TBI were performed systematically for each patient, and TBI was performed regardless of ABI or waveform. We examined associations between ABI, TBI, and the difference between them (ABI-TBI) with all-cause mortality and major adverse limb events (MALE), which includes revascularizations and amputations.

FINDINGS

The mean age was 65 years and 30% were African American. All patients were men, reflecting the Veterans Administration population. There were 26 deaths during follow-up and mortality was highest in patients who had low ABI and low TBI and least in those with high ABI and high TBI. Persons with TBI < 0.7 had an increased risk of all-cause mortality. The ABI-TBI, and the ABI itself, were not significantly associated with all-cause mortality although the patterns were similar.

DISCUSSION

Although ABI may be an important initial risk stratification tool, the TBI may be a more informative predictor of mortality in dialysis patients. Strengths of this study include a high rate of MALE and deaths. The TBI, and the difference between ABI and TBI, should be studied further in a larger cohort of persons with advanced kidney disease.

Patients,' Nephrologists,' and Predicted Estimations of ESKD Risk Compared with 2-Year Incidence of ESKD

BACKGROUND AND OBJECTIVES

The rate of progression to ESKD is variable, and prognostic information helps patients and physicians plan for future ESKD. We assessed the estimations of ESKD risk of patients with CKD and physicians and compared them with risk calculators and outcomes at 2 years.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This prospective observational study assessed 257 adult patients with CKD stages 3-5 and their nephrologists at University of California, San Diego and Veterans Affairs San Diego CKD clinics. Patients' and nephrologists' estimations of 2-year ESKD risk were evaluated, and objective estimation of 2-year risk was determined using kidney failure risk equations; actual incidence rates of ESKD and death were ascertained by chart review. Participants' baseline characteristics were compared across kidney failure risk equation risk levels and according to whether patients' estimations were more optimistic or pessimistic than physicians' estimations. We examined correlations between estimations and compared estimations with outcomes using c statistics and calibration plots.

RESULTS

Average age was 65 (±13) years old, and eGFR was 34 (±13) ml/min per 1.73 m². Overall, 13% reached ESKD, and 9% died. About one quarter of patients gave estimates that were >20% more optimistic than physicians, and more than one in ten gave estimates that were >20% more pessimistic. Physicians' and kidney failure risk equation estimations had the strongest correlation (r=0.72; P<0.001) compared with 0.50 (P<0.001) between physicians and patients and 0.47 (P<0.001) between patients and kidney failure risk equation. Although all three estimations provided reasonable risk rankings (c statistics >0.8), physicians and patients overestimated risk compared with actual outcomes; no patient whose physician estimated a risk of ESKD <15% reached ESKD at 2 years. The kidney failure risk equation was best calibrated to actual ESKD risk.

CONCLUSIONS

Compared with actual ESKD incidence, the kidney failure risk equation outperformed patients' and physicians' estimations of ESKD incidence. Patients and physicians overestimated risk compared with the kidney failure risk equation.

Relationship of acid-base status with arterial stiffness in community-living elders: the Health ABC Study

Background

Animal studies suggest that acidosis protects against arterial calcification, which contributes to arterial stiffness. The goal of this study was to investigate the associations of serum bicarbonate and pH with arterial stiffness in community-living older adults.

Methods

We performed cross-sectional analyses among 1698 well-functioning participants 70-79 years of age. Bicarbonate and pH were measured by arterialized venous blood gas at the point of care. Bicarbonate was categorized into low (<23 mEq/L), normal (23-27.9) and high (≥28). Arterialized venous pH (AVpH) was categorized into tertiles: ≤7.40, >7.40-7.42 and >7.42. Arterial stiffness was evaluated by pulse wave velocity (PWV) and high ankle-brachial index (ABI; >1.3/incompressible). We used linear and logistic regression to evaluate the association of bicarbonate and AVpH with PWV and high ABI, respectively.

Results

The mean age was 76 years and 15% had an estimated glomerular filtration rate (eGFR)  <60 mL/min/1.73 m2. The mean bicarbonate was 25.2 ± 2.1 mEq/L and the mean AVpH was 7.41 ± 0.03. Compared with participants in the normal bicarbonate category, those in the low bicarbonate group had 8.8% higher PWV (P = 0.006) and 1.87 greater odds of high ABI (P = 0.04). However, the associations were not significant after adjusting for eGFR (P = 0.24 and 0.43, respectively). There was no difference in PWV or high ABI across AVpH tertiles. Results were similar in those with and without chronic kidney disease and after excluding participants on diuretics.

Conclusions

We did not observe an independent association of bicarbonate or AVpH with arterial stiffness measured by high PWV or ABI in community-living older individuals. Future studies evaluating patients with a greater severity of chronic kidney disease and with more extreme alterations in acid-base status are warranted.

Serum Calcitriol Concentrations and Kidney Function Decline, Heart Failure, and Mortality in Elderly Community-Living Adults: The Health, Aging, and Body Composition Study

RATIONALE & OBJECTIVES

Lower 25-hydroxyvitamin D concentrations have been associated with risk for kidney function decline, heart failure, and mortality. However, 25-hydroxyvitamin D requires conversion to its active metabolite, calcitriol, for most biological effects. The associations of calcitriol concentrations with clinical events have not been well explored.

STUDY DESIGN

Case-cohort study.

SETTING & PARTICIPANTS

Well-functioning community-living older adults aged 70 to 79 years at inception who participated in the Health, Aging, and Body Composition (Health ABC) Study.

PREDICTOR

Serum calcitriol measured using positive ion electrospray ionization-tandem mass spectrometry.

OUTCOMES

Major kidney function decline (≥30% decline in estimated glomerular filtration rate from baseline), incident heart failure (HF), and all-cause mortality during 10 years of follow-up.

ANALYTIC APPROACH

Baseline calcitriol concentrations were measured in a random subcohort of 479 participants and also in cases with major kidney function decline [n=397]) and incident HF (n=207) during 10 years of follow-up. Associations of serum calcitriol concentrations with these end points were evaluated using weighted Cox regression to account for the case-cohort design, while associations with mortality were assessed in the subcohort alone using unweighted Cox regression.

RESULTS

During 8.6 years of mean follow-up, 212 (44%) subcohort participants died. In fully adjusted models, each 1-standard deviation lower calcitriol concentration was associated with 30% higher risk for major kidney function decline (95% CI, 1.03-1.65; P=0.03). Calcitriol was not significantly associated with incident HF (HR, 1.16; 95% CI, 0.94-1.47) or mortality (HR, 1.01; 95% CI, 0.81-1.26). We observed no significant interactions between calcitriol concentrations and chronic kidney disease status, baseline intact parathyroid or fibroblast factor 23 concentrations.

LIMITATIONS

Observational study design, calcitriol measurements at a single time point, selective study population of older adults only of white or black race.

CONCLUSIONS

Lower calcitriol concentrations are independently associated with kidney function decline in community-living older adults. Future studies will be needed to clarify whether these associations reflect lower calcitriol concentrations resulting from abnormal kidney tubule dysfunction or direct mechanisms relating lower calcitriol concentrations to more rapid loss of kidney function.

Relationship of femoral artery ultrasound measures of atherosclerosis with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is strongly associated with peripheral artery disease (PAD). Detection of subclinical PAD may allow early interventions for or prevention of PAD in persons with CKD. Whether the presence of atherosclerotic plaque and femoral intima-media thickness (IMT) are associated with kidney function is unknown.

METHODS

We performed a cross-sectional observational study of 1029 community-living adults. We measured superficial and common femoral artery IMT and atherosclerotic plaque presence by ultrasound. Estimated glomerular filtration rate (eGFR; continuous) and eGFR <60 mL/min/1.73 m2 (binary) were evaluated as outcomes.

RESULTS

Mean age was 70 ± 10 years, mean eGFR was 78 ± 17 mL/min/1.73 m2, and 156 (15%) individuals had eGFR <60 mL/min/1.73 m2; 260 (25%) had femoral artery plaque. In models adjusted for demographics and cardiovascular risk factors, individuals with femoral artery plaque had mean eGFR approximately 3.0 (95% confidence interval, -5.3 to -0.8) mL/min/1.73 m2 lower than those without plaque (P < .01). The presence of plaque was also associated with a 1.7-fold higher odds of eGFR <60 mL/min/1.73 m2 (95% confidence interval, 1.1-2.8; P < .02). Associations were similar in persons with normal ankle-brachial index. The directions of associations were similar for femoral IMT measures with eGFR and CKD but were rendered no longer statistically significant with adjustment for demographic variables and cardiovascular disease risk factors.

CONCLUSIONS

Femoral artery plaque is significantly associated with CKD prevalence in community-living individuals, even among those with normal ankle-brachial index. Femoral artery ultrasound may allow evaluation of relationships and risk factors linking PAD and kidney disease earlier in its course.

The 24,25 to 25-hydroxyvitamin D ratio and fracture risk in older adults: The cardiovascular health study

25-hydroxyvitamin D [25(OH)D] may not optimally indicate vitamin D receptor activity. Higher concentrations of its catabolic product 24,25-dihydroxyvitmin D [24,25(OH)₂D] and a higher ratio of 24,25(OH)₂D to 25(OH)D (the vitamin D metabolite ratio [VMR]) may provide additional information on receptor activity. We compared the strength of associations of these markers with serum PTH concentrations, hip bone mineral density (BMD), and risk of incident hip fracture in community-living older participants in the Cardiovascular Health Study. Among 890 participants, the mean age was 78years, 60% were women, and the mean 25(OH)D was 28±11ng/ml. In cross-sectional analysis, the strength of association of each vitamin D measure with PTH was similar; a 1% higher 25(OH)D, 24,25(OH)₂D, and VMR were associated with 0.32%, 0.25%, and 0.26% lower PTH, respectively (p<0.05 for all). Among 358 participants with available BMD data, we found no associations of 25(OH)D or VMR with BMD, whereas higher 24,25(OH)₂D was modestly associated with greater hip BMD (1% higher 24,25(OH)₂D associated with 0.04% [95% CI 0.01-0.08%] higher BMD). Risk of incident hip fracture risk was evaluated using a case-cohort design. There were 289 hip fractures during a mean follow up time of 8.4years. Both higher 24,25(OH)₂D and VMR were associated with lower risk of hip fracture (HR per SD higher, 0.73 [0.61, 0.87] and 0.74 [0.61, 0.88], respectively) whereas 25(OH)D was not associated with hip fracture (HR 0.93 [0.79, 1.10]). We conclude that evaluating vitamin D status by incorporating assessment of 24,25(OH)D and the VMR provides information on bone health above and beyond 25(OH)D alone.

Biomarkers of Key Biological Pathways in CVD

This review provides background on the laboratory design for MESA (Multi-Ethnic Study of Atherosclerosis) as well as the approach used in MESA to select biomarkers for measurement. The research related to the multitude of circulating and urinary biomarkers of inflammation and other novel and emerging biological pathways in MESA is summarized by domain, or pathway, represented by the biomarker. The contributions of MESA biomarkers to our knowledge of these key pathways in the development and progression of atherosclerosis, cardiovascular disease, diabetes, kidney disease, and pulmonary disease are highlighted, as are the contributions of MESA to recommendations for clinical use of several of these biomarkers. In addition, contributions of MESA to multicohort genomics consortia and current collaborations in transomics and metabolomics are noted.

The Effect of Extended Release Niacin on Markers of Mineral Metabolism in CKD

BACKGROUND AND OBJECTIVES

Niacin downregulates intestinal sodium-dependent phosphate transporter 2b expression and reduces intestinal phosphate transport. Short-term studies have suggested that niacin lowers serum phosphate concentrations in patients with CKD and ESRD. However, the long-term effects of niacin on serum phosphate and other mineral markers are unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglycerides: Impact on Global Health Trial was a randomized, double-blind, placebo-controlled trial testing extended release niacin in persons with prevalent cardiovascular disease. We examined the effect of randomized treatment with niacin (1500 or 2000 mg) or placebo on temporal changes in markers of mineral metabolism in 352 participants with eGFR<60 ml/min per 1.73 m2 over 3 years. Changes in each marker were compared over time between the niacin and placebo arms using linear mixed effects models.

RESULTS

Randomization to niacin led to 0.08 mg/dl lower plasma phosphate concentrations per year of treatment compared with placebo (P<0.01) and 0.25 mg/dl lower mean phosphate 3 years after baseline (3.32 versus 3.57 mg/dl; P=0.03). In contrast, randomization to niacin was not associated with statistically significant changes in plasma intact fibroblast growth factor 23, parathyroid hormone, calcium, or vitamin D metabolites over 3 years.

CONCLUSIONS

The use of niacin over 3 years lowered serum phosphorous concentrations but did not affect other markers of mineral metabolism in participants with CKD.

Relation Between Calcified Atherosclerosis in the Renal Arteries and Kidney Function (from the Multi-Ethnic Study of Atherosclerosis)

Renal artery calcium (RAC) has been shown to be associated with higher odds of hypertension (HTN). The purpose of this study was to determine if the presence and extent of RAC is associated with renal function. We analyzed cross-sectional data from the Multi-Ethnic Study of Atherosclerosis (MESA). A subsample of 1,226 participants underwent computed tomography of the abdomen and also had venous blood samples measured for kidney function. RAC was the primary predictor variable and the following measures of kidney function were the outcome variables: estimated glomerular filtration rate (eGFR), urinary albumin-to-creatinine ratio (UACR), and chronic kidney disease (CKD) stage. The analyses were adjusted for age, gender, race, height, visceral fat, dyslipidemia, diabetes, cigarette smoking, hypertension, interleukin-6 and abdominal aortic calcium (AAC). The average age of this cohort was 66.1 years (SD 9.7), 44.8% (549 of 1,226) were men, and nearly 30% had RAC >0. Compared with those with no RAC, those with RAC >0 were significantly older but not different by gender or race. After adjustment for age, gender, and race, those with RAC >0 had significantly higher visceral fat, were more likely to have dyslipidemia, diabetes, and hypertension, had a higher interleukin-6, and a higher prevalence of AAC >0. The mean eGFR and UACR among those without RAC were 80 ml/min/1.73 m² and 21 mg/g, whereas these values were 78 ml/min/1.73 m² and 55 mg/g among those with RAC. In fully adjusted multivariable linear regression models, the presence of RAC was associated with a lower eGFR (β = -2.21, p = 0.06) but not with UACR (β = 0.02, p = 0.79). In fully adjusted ordinal logistic regression, RAC as a continuous variable was associated with increased odds of being in a worse CKD category (odds ratio 1.14, p = 0.05). When measured by eGFR and CKD stage, there is a modest relation between RAC and kidney function. Further studies might involve clinical trials to assess the role of intensive cardiovascular disease risk factor management in patients with subclinical RAC to determine if this may prevent or delay the development and progression of CKD.

Variation in Sodium Intake and Intra-individual Change in Blood Pressure in Chronic Kidney Disease

OBJECTIVE

In the kidney disease clinic setting, higher-than-usual blood pressure is often ascribed to recent dietary sodium indiscretion. While clinical trials demonstrate a clear relationship between salt intake and blood pressure on the population level, it is uncertain whether real-world variation in sodium intake within individual chronic kidney disease (CKD) patients is associated with fluctuations in blood pressure.

METHODS

We analyzed data from the Phosphorus Normalization Trial, in which participants with CKD eating their usual diets completed at least three 24-hour urine collections over 9 months, from which we measured sodium. Blood pressure was measured at the time of 24-hour urine collections. For each individual participant, we assessed the slope of the relationship between sodium intake and mean arterial blood pressure (MAP).

RESULTS

Among 119 participants (mean age 67 years and mean estimated glomerular filtration rate 31 mL/minute/1.73 m²), there was substantial variation in sodium intake as measured by 24-hour urine collections (mean intake 3,903 mg/day, standard deviation 1037 mg/day). Individual participants had highly variable associations between their sodium intake and their MAP; 47% (n = 56) had inverse associations between sodium and MAP, whereas the remainder had positive (salt-sensitive) associations.

CONCLUSIONS

Among CKD patients, there is substantial variation in sodium intake but no predictable relationship between dietary sodium and blood pressure in individuals. The frequent dismissal of elevated blood pressure readings as related to recent sodium intake in clinic may be a misapplication of large-scale population data to explain individual variability and may contribute to clinical inertia regarding high blood pressure treatment.

Association of cardiovascular disease risk factors with coronary artery calcium volume versus density

OBJECTIVES

Recently, the density score of coronary artery calcium (CAC) has been shown to be associated with a lower risk of cardiovascular disease (CVD) events at any level of CAC volume. Whether risk factors for CAC volume and CAC density are similar or distinct is unknown. We sought to evaluate the associations of CVD risk factors with CAC volume and CAC density scores.

METHODS

Baseline measurements from 6814 participants free of clinical CVD were collected for the Multi-Ethnic Study of Atherosclerosis. Participants with detectable CAC (n=3398) were evaluated for this study. Multivariable linear regression models were used to evaluate independent associations of CVD risk factors with CAC volume and CAC density scores.

RESULTS

Whereas most CVD risk factors were associated with higher CAC volume scores, many risk factors were associated with lower CAC density scores. For example, diabetes was associated with a higher natural logarithm (ln) transformed CAC volume score (standardised β=0.44 (95% CI 0.31 to 0.58) ln-units) but a lower CAC density score (β=-0.07 (-0.12 to -0.02) density units). Chinese, African-American and Hispanic race/ethnicity were each associated with lower ln CAC volume scores (β=-0.62 (-0.83to -0.41), -0.52 (-0.64 to -0.39) and -0.40 (-0.55 to -0.26) ln-units, respectively) and higher CAC density scores (β= 0.41 (0.34 to 0.47), 0.18 (0.12 to 0.23) and 0.21 (0.15 to 0.26) density units, respectively) relative to non-Hispanic White.

CONCLUSIONS

In a cohort free of clinical CVD, CVD risk factors are differentially associated with CAC volume and density scores, with many CVD risk factors inversely associated with the CAC density score after controlling for the CAC volume score. These findings suggest complex associations between CVD risk factors and these components of CAC.

Femoral Artery Atherosclerosis Is Associated With Physical Function Across the Spectrum of the Ankle-Brachial Index: The San Diego Population Study

Background

The ankle‐brachial index (ABI) is inadequate to detect early‐stage atherosclerotic disease, when interventions to prevent functional decline may be the most effective. We determined associations of femoral artery atherosclerosis with physical functioning, across the spectrum of the ABI, and within the normal ABI range.

Methods and Results

In 2007–2011, 1103 multiethnic men and women participated in the San Diego Population Study, and completed all components of the summary performance score. Using Doppler ultrasound, superficial and common femoral intima media thickness and plaques were ascertained. Logistic regression was used to assess associations of femoral atherosclerosis with the summary performance score and its individual components. Models were adjusted for demographics, lifestyle factors, comorbidities, lipids, and kidney function. In adjusted models, among participants with a normal‐range ABI (1.00–1.30), the highest tertile of superficial intima media thickness was associated with lower odds of a perfect summary performance score of 12 (odds ratio=0.56 [0.36, 0.87], P=0.009), and lower odds of a 4‐m walk score of 4 (0.34 [0.16, 0.73], P=0.006) and chair rise score of 4 (0.56 [0.34, 0.94], P=0.03). Plaque presence (0.53 [0.29, 0.99], P=0.04) and greater total plaque burden (0.61 [0.43, 0.87], P=0.006) were associated with worse 4‐m walk performance in the normal‐range ABI group. Higher superficial intima media thickness was associated with lower summary performance score in all individuals (P=0.02).

Conclusions

Findings suggest that use of femoral artery atherosclerosis measures may be effective in individuals with a normal‐range ABI, especially, for example, those with diabetes mellitus or a family history of peripheral artery disease, when detection can lead to earlier intervention to prevent functional declines and improve quality of life.

Greater Volume but not Higher Density of Abdominal Aortic Calcium Is Associated With Increased Cardiovascular Disease Risk: MESA (Multi-Ethnic Study of Atherosclerosis)

BACKGROUND

Abdominal aortic calcium (AAC) and coronary artery calcium (CAC) independently and similarly predict cardiovascular disease (CVD) events. The standard AAC and CAC score, the Agatston method, upweights for greater calcium density, thereby modeling higher calcium density as a CVD hazard.

METHODS AND RESULTS

Computed tomography scans were used to measure AAC and CAC volume and density in a multiethnic cohort of community-dwelling individuals, and Cox proportional hazard was used to determine their independent association with incident coronary heart disease (CHD, defined as myocardial infarction, resuscitated cardiac arrest, or CHD death), cardiovascular disease (CVD, defined as CHD plus stroke and stroke death), and all-cause mortality. In 997 participants with Agatston AAC and CAC scores >0, the mean age was 66±9 years, and 58% were men. During an average follow-up of 9 years, there were 77 CHD, 118 CVD, and 169 all-cause mortality events. In mutually adjusted models, additionally adjusted for CVD risk factors, an increase in ln(AAC volume) per standard deviation was significantly associated with increased all-cause mortality (hazard ratio=1.20; 95% confidence interval, 1.08-1.33; P<0.01) and an increased ln(CAC volume) per standard deviation was significantly associated with CHD (hazard ratio=1.17; 95% confidence interval, 1.04-1.59; P=0.02) and CVD (hazard ratio=1.20; 95% confidence interval, 1.05-1.36; P<0.01). In contrast, both AAC and CAC density were not significantly associated with CVD events.

CONCLUSIONS

The Agatston method of upweighting calcium scores for greater density may be inappropriate for CVD risk prediction in both the abdominal aorta and coronary arteries.

The Relation of Serum Potassium Concentration with Cardiovascular Events and Mortality in Community-Living Individuals

BACKGROUND AND OBJECTIVES

Hyperkalemia is associated with adverse outcomes in patients with CKD and in hospitalized patients with acute medical conditions. Little is known regarding hyperkalemia, cardiovascular disease (CVD), and mortality in community-living populations. In a pooled analysis of two large observational cohorts, we investigated associations between serum potassium concentrations and CVD events and mortality, and whether potassium-altering medications and eGFR<60 ml/min per 1.73 m2 modified these associations.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Among 9651 individuals from the Multi-Ethnic Study of Atherosclerosis (MESA) and the Cardiovascular Health Study (CHS), who were free of CVD at baseline (2000-2002 in the MESA and 1989-1993 in the CHS), we investigated associations between serum potassium categories (<3.5, 3.5-3.9, 4.0-4.4, 4.5-4.9, and ≥5.0 mEq/L) and CVD events, mortality, and mortality subtypes (CVD versus non-CVD) using Cox proportional hazards models, adjusting for demographics, time-varying eGFR, traditional CVD risk factors, and use of potassium-altering medications.

RESULTS

Compared with serum potassium concentrations between 4.0 and 4.4 mEq/L, those with concentrations ≥5.0 mEq/L were at higher risk for all-cause mortality (hazard ratio, 1.41; 95% confidence interval, 1.12 to 1.76), CVD death (hazard ratio, 1.50; 95% confidence interval, 1.00 to 2.26), and non-CVD death (hazard ratio, 1.40; 95% confidence interval, 1.07 to 1.83) in fully adjusted models. Associations of serum potassium with these end points differed among diuretic users (Pinteraction<0.02 for all), such that participants who had serum potassium ≥5.0 mEq/L and were concurrently using diuretics were at higher risk of each end point compared with those not using diuretics.

CONCLUSIONS

Serum potassium concentration ≥5.0 mEq/L was associated with all-cause mortality, CVD death, and non-CVD death in community-living individuals; associations were stronger in diuretic users. Whether maintenance of potassium within the normal range may improve clinical outcomes requires future study.

Kidney Function and Disability-Free Survival in Older Women

OBJECTIVES

To examine the prospective association between kidney function and three outcomes: survival to age 85 with functional independence, survival to age 85 with disability, and death before age 85.

DESIGN

Prospective study.

SETTING

Women's Health Initiative, conducted at 40 U.S. clinical centers.

PARTICIPANTS

Postmenopausal women enrolled between 1993 and 1998 with baseline biomarker assessments who had the potential to reach age 85 before September 2013 (N = 7,178).

MEASUREMENTS

Kidney function was measured according to estimated glomerular filtration rate (eGFR) calculated from serum creatinine collected at baseline. Outcomes were survival to age 85 with functional independence, survival with disability, or death before age 85. Disability was defined as mobility or activity of daily living limitations measured by questionnaire.

RESULTS

eGFR was greater than 90 mL/min per 1.73 m2 in 22.7% of women, 60 to 89 mL/min per 1.73 m2 in 66.5%, 45 to 59 mL/min per 1.73 m2 in 8.7%, and less than 45 mL/min per 1.73 m2 in 2.0%. Median follow-up was 15 years. Of 4,953 survivors, 3,155 reported no physical disability at age 85. Two thousand two hundred twenty-five participants died before age 85. Women with an eGFR of 90 mL/min per 1.73 m2 or greater had 2.71 times greater odds of survival to age 85 with functional independence than of dying before 85 (95% confidence interval (CI) = 1.62-4.51) than those with an eGFR less than 45 mL/min per 1.73 m2 , women with an eGFR of 60 to 89 mL/min per 1.73 m2 had 3.04 times (95% CI = 1.85-5.00) greater odds, and women with an eGFR of 45 to 59 mL/min per 1.73 m2 had 2.22 times (95% CI = 1.31-3.76) greater odds. Similar, but slightly weaker odds were seen for survival to age 85 with disability. Better kidney function was not significantly associated with greater likelihood of survival to age 85 with independent function than of surviving with disability.

CONCLUSION

Better kidney function was associated with greater likelihood of survival to age 85 with and without disability.

Associations between cystatin C-based eGFR, ambulatory blood pressure parameters, and in-clinic versus ambulatory blood pressure agreement in older community-living adults

OBJECTIVES

The objective of this study was to determine the relationship between chronic kidney disease [CKD; measured using cystatin C-based estimated glomerular filtration rate (eGFR)] and abnormal ambulatory blood pressure (including nocturnal dipping) in healthy older adults. Further, this study aimed to assess the agreement between clinic and ambulatory blood pressure monitoring.

METHODS

Serum cystatin C levels were measured to calculate eGFR. Participants underwent clinic and 24-h ambulatory blood pressure measurements. Multiple linear regression was performed to examine the association between reduced cystatin C-based eGFR (CKDcys) and blood pressure parameters. Bland-Altman analysis was carried out to evaluate the agreement between clinic and ambulatory measurements.

RESULTS

The average age was 72 years. There were 60 individuals with CKDcys (eGFR<60 ml/min/1.73 m). Compared with those without CKDcys, individuals with CKDcys were older, more likely to have hypertension, and less likely to have normal dipping patterns. On multivariate analysis, the presence of CKDcys was found to be significantly associated with a lower mean ambulatory diastolic blood pressure (-2 mmHg, P=0.048), but not with nocturnal dipping or other blood pressure parameters. Clinic systolic blood pressure (SBP) significantly overestimated the mean wake-time ambulatory SBP; the mean difference was 11 mmHg for those without CKDcys (95% limits of agreement -14 to 35 mmHg) and 14 mmHg for those with CKDcys (95% limits of agreement -13 to 41 mmHg); there was no statistically significant effect modification by CKD status.

CONCLUSION

In older, seemingly healthy adults, mild CKD was associated with lower ambulatory diastolic blood pressure. The presence of CKD did not affect interpretation of clinic versus ambulatory blood pressure monitoring, although the accuracy of clinic SBP was poor.

Effect of Intensive Versus Standard Clinic-Based Hypertension Management on Ambulatory Blood Pressure: Results From the SPRINT (Systolic Blood Pressure Intervention Trial) Ambulatory Blood Pressure Study

The effect of clinic-based intensive hypertension treatment on ambulatory blood pressure (BP) is unknown. The goal of the SPRINT (Systolic Blood Pressure Intervention Trial) ambulatory BP ancillary study was to evaluate the effect of intensive versus standard clinic-based BP targets on ambulatory BP. Ambulatory BP was obtained within 3 weeks of the 27-month study visit in 897 SPRINT participants. Intensive treatment resulted in lower clinic systolic BP (mean difference between groups=16.0 mm Hg; 95% confidence interval, 14.1-17.8 mm Hg), nighttime systolic BP (mean difference=9.6 mm Hg; 95% confidence interval, 7.7-11.5 mm Hg), daytime systolic BP (mean difference=12.3 mm Hg; 95% confidence interval, 10.6-13.9 mm Hg), and 24-hour systolic BP (mean difference=11.2 mm Hg; 95% confidence interval, 9.7-12.8 mm Hg). The night/day systolic BP ratio was similar between the intensive (0.92±0.09) and standard-treatment groups (0.91±0.09). There was considerable lack of agreement within participants between clinic systolic BP and daytime ambulatory systolic BP with wide limits of agreement on Bland-Altman plots. In conclusion, targeting a systolic BP of <120 mm Hg, when compared with <140 mm Hg, resulted in lower nighttime, daytime, and 24-hour systolic BP, but did not change the night/day systolic BP ratio. Ambulatory BP monitoring may be required to assess the effect of targeted hypertension therapy on out of office BP. Further studies are needed to assess whether targeting hypertension therapy based on ambulatory BP improves clinical outcomes.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01835249.

Nutrition Interventions in Chronic Kidney Disease

Dietary modification is recommended in the management of chronic kidney disease (CKD). Individuals with CKD often have multiple comorbidities, such as high blood pressure, diabetes, obesity, and cardiovascular disease, for which dietary modification is also recommended. As CKD progresses, nutrition plays an important role in mitigating risk for cardiovascular disease and decline in kidney function. The objectives of nutrition interventions in CKD include management of risk factors, ensuring optimal nutritional status throughout all stages of CKD, preventing buildup of toxic metabolic products, and avoiding complications of CKD. Recommended dietary changes should be feasible, sustainable, and suited for patients' food preferences and clinical needs.

Associations of cardiovascular disease risk factors with abdominal aortic calcium volume and density: The Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND AND AIMS

Abdominal aortic calcium (AAC) predicts future cardiovascular disease (CVD) events and all-cause mortality independent of CVD risk factors. The standard AAC score, the Agatston, up-weights for greater calcium density, and thus models higher calcium density as associated with increased CVD risk. We determined associations of CVD risk factors with AAC volume and density (separately).

METHODS

In a multi-ethnic cohort of community living adults, we used abdominal computed tomography scans to measure AAC volume and density. Multivariable linear regression was used to determine the period cross-sectional independent associations of CVD risk factors with AAC volume and AAC density in participants with prevalent AAC.

RESULTS

Among 1413 participants with non-zero AAC scores, the mean age was 65 ± 9 years, 52% were men, 44% were European-, 24% were Hispanic-, 18% were African-, and 14% were Chinese Americans (EA, HA, AA, and CA respectively). Median (interquartile range, IQR) for AAC volume was 628 mm³ (157-1939 mm³), and mean AAC density was 3.0 ± 0.6. Compared to EA, each of HA, AA, and CA had lower natural log (ln) AAC volume, but higher AAC density. After adjustments for AAC density, older age, ever smoking history, higher systolic blood pressure, elevated total cholesterol, reduced HDL cholesterol, statin and anti-hypertensive medication use, family history of myocardial infarction, and alcohol consumption were significantly associated with higher ln(AAC volume). In contrast, after adjustments for ln(AAC volume), older age, ever smoking history, higher BMI, and lower HDL cholesterol were significantly associated with lower AAC density.

CONCLUSIONS

Several CVD risk factors were associated with higher AAC volume, but lower AAC density. Future studies should investigate the impact of calcium density of aortic plaques in CVD.