Association between serum bicarbonate levels and albuminuria in stage 3 and stage 4 chronic kidney disease: a cross-sectional study

Aims: Metabolic acidosis is a common manifestation of chronic kidney disease (CKD) and appears to be associated with CKD progression and mortality. We evaluated whether serum bicarbonate level is associated with albuminuria in patients with stage 3 and 4 CKD. Methods: This was a retrospective cross-sectional study of outpatients with CKD stages 3 - 4 (estimated glomerular filtration rate 15 -59 mL/minutes/1.73 m(2)). Serum bicarbonate levels, serum creatinine levels, and random urinary albumin-to-creatinine ratios (UA/Cr) examined on the same day were required for enrollment. Significant albuminuria was defined as UA/Cr >= 300 mg/g. Serum bicarbonate was analyzed as both a continuous variable and a categorical variable after it was divided into categories of < 23, 23 - 25.9, and >= 26 mmol/L. Results: 151 patients were included in this study. Their mean age was 59.1 +/- 13.9 years, and 60.9% were men. The mean serum bicarbonate level was 23.7 +/- 3.3 mmol/L. In a multiple logistic regression analysis to determine the factors associated with significant albuminuria, the serum bicarbonate categories were independent factors associated with significant albuminuria after adjustments were made for relevant co-variates (p = 0.028). In a subgroup analysis according to CKD stage, the association between bicarbonate categories and significant albuminuria was significant only for patients with stage 3 disease, regardless of renal function or blood pressure (p = 0.014 and 0.706 in stage 3 and 4 diseases, respectively). Conclusions: Low serum bicarbonate levels were associated with significant albuminuria, even at levels in the normal range, in CKD patients, especially with stage 3 disease.