Metabolic Acidosis and Adverse Outcomes and Costs in CKD: An Observational Cohort Study

RATIONALE & OBJECTIVE: Metabolic acidosis is a risk factor for progression of chronic kidney disease (CKD), but little is known about its effect on health care costs and resource utilization. We describe the associations between metabolic acidosis, adverse kidney outcomes, and health care costs in patients with CKD stages G3-G5 and not receiving dialysis. STUDY DESIGN: Retrospective cohort study. SETTING & PARTICIPANTS: An integrated claims-clinical data set of US patients with CKD stages G3-G5, with serum bicarbonate values of 12 to <22 mEq/L (metabolic acidosis group) or 22 to 29 mEq/L (normal serum bicarbonate level group). PREDICTOR: The primary exposure variable was the baseline serum bicarbonate level. OUTCOMES: The primary clinical outcome was the composite of all-cause mortality, maintenance dialysis, kidney transplant, or a decline in the estimated glomerular filtration rate of ≥40% (DD40). The primary cost outcome was all-cause predicted per-patient per-year cost, assessed over a 2-year outcome period. ANALYTICAL APPROACH: Logistic and generalized linear regression models, adjusted for key covariates such as age, sex, race, kidney function, comorbidities, and pharmacy insurance coverage, were used to assess serum bicarbonate levels as a predictor of DD40 and health care costs, respectively. RESULTS: 51,558 patients qualified. The metabolic acidosis group experienced higher rates of DD40 (48.3% vs. 16.7%, P < 0.001) and higher all-cause yearly costs ($65,172 vs. $24,681, P < 0.001). Two-year adjusted odds ratio of DD40 per 1-mEq/L increase in serum bicarbonate levels was 0.873 (95% CI, 0.866-0.879); the parameter estimate (±SE) for costs was −0.070 ± 0.0075 (P < 0.001). LIMITATIONS: Possible residual confounding. CONCLUSIONS: Patients with CKD and metabolic acidosis had higher costs and rates of adverse kidney outcomes compared with patients with normal serum bicarbonate levels. Each 1-mEq/L increase in serum bicarbonate levels was associated with a 13% decrease in 2-year DD40 events and a 7% decrease in per-patient per-year cost.