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

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 m 2 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 m 2 with a rate of loss of at least 1 mL/min/1.73 m 2 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 m 2 . Results: At baseline, mean eGFR was 84 6 16 (SD) mL/min/1.73 m 2 , and serum bicarbonate level was 25.2 6 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 5 85 [8%]) lost eGFR 0.55 (95% CI, 0.13-0.97) mL/min/1.73 m 2 peryearfasterinmodelsadjustedfordemographics,CKDriskfactors,baselineeGFR,andurinealbumin-creatinine ratio.Amongthe989(92%)participantswithbaselineeGFRs . 60 mL/min/1.73 m 2 ,252(25%)developedincident eGFRs , 60 mL/min/1.73 m 2 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 m 2 (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 m 2 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.