Original Investigation
Pathogenesis and Treatment of Kidney Disease
Serum Bicarbonate Concentrations and Kidney Disease Progression in Community-Living Elders: The Health, Aging, and Body Composition (Health ABC) Study

https://doi.org/10.1053/j.ajkd.2014.05.009Get rights and content

Background

In populations with prevalent chronic kidney disease (CKD), lower serum bicarbonate levels are associated with more rapid CKD progression, but whether lower bicarbonate levels also are associated with risk of incident estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2 and CKD progression among community-living persons with predominantly preserved kidney function is unknown.

Study Design

Longitudinal observational cohort study.

Setting & Participants

Well-functioning community-living elders aged 70-79 years at inception.

Predictor

Serum bicarbonate level measured at the time of collection by arterialized venous blood sample using an arterial blood gas analyzer.

Outcomes

Change in eGFR over 7 years, and new eGFR < 60 mL/min/1.73 m2 with a rate of loss of at least 1 mL/min/1.73 m2 per year.

Measurements

Linear and logistic regressions were used to evaluate associations of baseline serum bicarbonate level with change in eGFR and incident eGFR < 60 mL/min/1.73 m2.

Results

At baseline, mean eGFR was 84 ± 16 (SD) mL/min/1.73 m2, and serum bicarbonate level was 25.2 ± 1.9 mmol/L. Compared with participants with higher bicarbonate concentrations (23.0-28.0 mmol/L), those with bicarbonate concentrations < 23 mmol/L (n = 85 [8%]) lost eGFR 0.55 (95% CI, 0.13-0.97) mL/min/1.73 m2 per year faster in models adjusted for demographics, CKD risk factors, baseline eGFR, and urine albumin-creatinine ratio. Among the 989 (92%) participants with baseline eGFRs > 60 mL/min/1.73 m2, 252 (25%) developed incident eGFRs < 60 mL/min/1.73 m2 at follow-up. Adjusting for the same covariates, participants with bicarbonate concentrations < 23 mmol/L had nearly 2-fold greater odds of incident eGFRs < 60 mL/min/1.73 m2 (OR, 1.72; 95% CI, 0.97-3.07) compared with those with higher bicarbonate concentrations.

Limitations

Only 2 measurements of kidney function separated by 7 years and loss to follow-up due to intervening mortality in this elderly population.

Conclusions

Lower serum bicarbonate concentrations are associated independently with decline in eGFR and incident eGFR < 60 mL/min/1.73 m2 in community-living older persons. If confirmed, serum bicarbonate levels may give insight into kidney tubule health in persons with preserved eGFRs and suggest a possible new target for intervention to prevent CKD development.

Section snippets

Study Population

The Health ABC cohort enrolled 3,075 well-functioning men and women aged 70-79 years from 2 clinical sites in Memphis, TN, and Pittsburgh, PA, from April 1997 through June 1998. Participant eligibility required self-reported ability to walk a quarter mile, climb 10 steps, perform basic activities of daily living without difficulty, the absence of life-threatening illness, and plans to remain in the geographic area for at least 3 years. Participants underwent a baseline evaluation that included

Results

By necessity, we excluded individuals who presented to the baseline examination but ultimately did not have sufficient data for analysis due to death or missing follow-up kidney function data. Compared to those with available data, those without were older, were more frequently black, were more likely to be current smokers, had higher ACRs, had more diabetes and obstructive lung disease, and had higher systolic blood pressures. Other variables including baseline eGFR were similar (Table S1,

Discussion

Among well-functioning community-living elders predominantly with preserved kidney function at baseline, we found that lower serum bicarbonate concentrations were associated with more rapid loss of kidney function over time. Within the subset of persons with eGFRs > 60 mL/min/1.73 m2 at baseline, lower serum bicarbonate concentrations were associated with the development of incident eGFRs < 60 mL/min/1.73 m2 during follow-up. These associations became apparent in individuals with serum bicarbonate

Acknowledgements

The Health ABC Study Principal Investigators and Coordinators are as follows: Anne B. Newman, MD, MPH, Piera Kost, Diane Ives, University of Pittsburgh, PA; Suzanne Satterfield, MD, DrPH, Frances A. Tylavsky, DrPH, Jan Elam, University of Tennessee, Memphis; Stephen B. Kritchevsky, PhD, Wake Forest University, Winston-Salem, NC; Steven R. Cummings, MD, Michael C. Nevitt, PhD, Susan M. Rubin, MPH, University of California, San Francisco; and Tamara B. Harris, MD, Melissa E. Garcia, MPH, National

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Because the Editor-in-Chief and Deputy Editor recused themselves from consideration of this manuscript, the peer-review and decision-making processes were handled entirely by a Co-Editor (James S. Kaufman, MD) who served as Acting Editor-in-Chief. Details of the journal’s procedures for potential editor conflicts are given in the Information for Authors & Editorial Policies.

A list of the Health ABC Study principal investigators and coordinators appears in the Acknowledgements.

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