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) 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 2 with a rate of loss of at least 1mL/min/1.73m 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 2 . Results At baseline, mean eGFR was 84±16 (SD)mL/min/1.73m 2 , and serum bicarbonate level was 25.2±1.9mmol/L. Compared with participants with higher bicarbonate concentrations (23.0-28.0mmol/L), those with bicarbonate concentrations 2 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>60mL/min/1.73m 2 , 252 (25%) developed incident eGFRs 2 at follow-up. Adjusting for the same covariates, participants with bicarbonate concentrations 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 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.