Obesity, Anion Accumulation, and Anion Gap Metabolic Acidosis: A Cohort Study

Background: Obesity is associated with low serum bicarbonate, an indicator of metabolic acidosis and a CKD risk factor. To further characterize acid-base disturbance and subclinical metabolic acidosis in this population, we examined prospective associations of body mass index (BMI) with elevated anion gap, and whether anion gap values in obesity associate with low bicarbonate. Methods: Data from adult outpatients (n = 94,448) in the Bronx, NY were collected from 2010-2018. Mixed effects models and Cox proportional hazards models were used to examine associations of BMI with elevated anion gap and anion gap metabolic acidosis, and of baseline anion gap with incident low bicarbonate and anion gap metabolic acidosis. Anion gap was defined using traditional and albumin-corrected calculations. Results: Greater BMI was associated with higher anion gap over time, and with progressively greater risk of developing an elevated anion gap (HRs for BMI ≥ 40 vs. 18-<25 kg/m2: 1.32 [95% CI: 1.23 - 1.42] for traditional and 1.74 [95% CI: 1.63 - 1.85] for corrected). Higher BMI was also associated with increased risk of developing anion gap metabolic acidosis (HR for BMI ≥ 40: 1.53 [95% CI: 1.39 - 1.69]). Among patients with obesity, higher anion gap was associated with increased risk of incident low bicarbonate (HRs for 4th vs 1st quartile: 1.29 [95% CI: 1.23 - 1.44] for traditional and 1.36 [95% CI: 1.26 - 1.48] for corrected); and higher risk of anion gap metabolic acidosis (HR for 4th vs 1st quartile 1.78 [1.59 - 1.99]). Conclusions: Obesity is characterized by unmeasured anion accumulation and acid retention or overproduction. Modest elevations in anion gap among patients with obesity are associated with previously unrecognized anion gap metabolic acidosis.

Effects of glucocorticoid steroids on renal and systemic acid-base metabolism

Clinical states of hyperglucocorticoidism are associated with renal metabolic alkalosis, yet the systemic and renal acid-base response to chronic administration of glucocorticoid steroids (dexamethasone, triamcinolone) possessing little or no mineralocorticoid activity has not been investigated. In balance studies studies in dogs administration of triamcinolone (Tcn), 1.0 mg. kg-1. day-1 for 6–9 days (group I, n = 5), resulted in a persistent reduction in urine pH and increase in net acid excretion (NAE), and in the excretion of urinary unmeasured anions (C+NH4,Na;K minus A-Cl,HCO3,Pi), which were identified as organic anions and sulfate. A significant degree of metabolic acidosis occurred initially (delta [HCO3-]p, -3.4 meq/liter, P less than 0.05, day 1). As Tcn administration was continued, the cumulative increment in net acid excreted exceeded the cumulative increment in urinary unmeasured anion excreted and [HCO-3]p returned to pre-Tcn control values and remained stable thereafter. In the steady state of Tcn administration plasma potassium concentration and renal potassium clearance were not significantly different from pre-Tcn control, in contrast to the findings of hypokalemia and increased renal potassium clearance during chronic administration of deoxycorticosterone (DOC). Triamcinolone did not result in antinatriuresis or antichloruresis. Chronic administration of a 10–fold smaller dose of Tcn (0.1 mg . kg-1 . day-1) in an additional group (group III) also resulted in a persisting reduction in urine pH and an increase in net acid excretion that exceeded unmeasured anion excretion and resulted in a small increase in steady-state plasma bicarbonate concentration. These results suggest that chronic administration of potent glucocorticoid steroids results in 1) a persisting increase in endogenous acid production, and 2) stimulation of renal hydrogen ion secretion that was of greater degree than accounted for by the increment in endogenous acid production and that was not accompanied by renal mineralocorticoid effects on sodium and potassium transport.