Kidney Week

Abstract: FR-PO201

Urine Citrate Excretion Non-Invasively Identifies Changes in Acid Retention over Time in CKD 2 Patients Without Metabolic Acidosis

Session Information

• CKD: Epidemiology, Risk Factors, Prevention - II
  October 26, 2018 | Location: Exhibit Hall, San Diego Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: CKD (Non-Dialysis)

• 1901 CKD (Non-Dialysis): Epidemiology, Risk Factors, and Prevention

Authors

• Goraya, Nimrit, Baylor Scott and White Health, Temple, Texas, United States

Nimrit Goraya,

• Simoni, Jan, Texas Tech University Health Sciences Center, Lubbock, Texas, United States

Jan Simoni,

• Sager, Lauren N., Baylor Scott & White, Temple, Texas, United States

Lauren N. Sager,

• Madias, Nicolaos E., Tufts University School of Medicine, Boston, Massachusetts, United States

Nicolaos E. Madias,

• Wesson, Donald E., Baylor Scott and White Health and Wellness Center, Dallas, Texas, United States

Donald E. Wesson,

Background

Some CKD stage 2 (eGFR=60-89 ml/min/1.73 m², CKD 2) patients without metabolic acidosis (conventionally defined as plasma total CO₂ <22 mM) nevertheless have acid (H⁺) retention that appears to exacerbate nephropathy progression, increases as eGFR decreases over time (Goraya et al, AJP, 2018), and this increase in H⁺ retention might be ameliorated with chronic oral NaHCO₃. Current methods to measure H⁺ retention are cumbersome and invasive so we explored the utility of urine citrate excretion to non-invasively identify changes in H⁺ retention over time.

Methods

We measured H⁺ retention and 8-hour urine citrate excretion (U_citrateV) in macroalbuminuric, non-diabetic CKD 2 patients with hypertension-associated nephropathy without metabolic acidosis (plasma total CO₂ >24 mM) given 0.5 meq/kg bw/day NaHCO₃ (HCO₃, n=40), 0.5 meq/kg bw/day NaCl (NaCl, n=40), or usual care (UC, n=40) and assessed them yearly for 10 years. H⁺ retention was measured at baseline and 10 years by comparing observed to expected increase in plasma total CO₂ in response to retained HCO₃ (dose minus U_HCO3V) 2 hours after oral NaHCO₃ bolus (0.5 mmol/kg bw), assuming 50% body weight HCO₃ apparent space of distribution.

Results

Baseline H⁺ retention and U_citrateV were not different among groups. The 10-year vs. respective baseline value in HCO₃ was not different for H⁺ retention (15.7±12.6 vs. 18.1±14.9 mmol, p=0.90) or U_citrateV (204±43 vs. 195±49 mg, respectively, p=0.30). By contrast, the 10-year vs. respective baseline value in NaCl was higher for H⁺ retention (27.5±15.2 vs. 19.2±16.7 mmol, respectively, p<0.01) and lower for U_citrateV (158±47 vs. 193±52 mg, respectively, p<0.01). Similar to NaCl, 10-year vs. respective baseline value in UC was higher for H⁺ retention (22.1±11.2 vs. 17.4±9.9 mmol, respectively, p<0.01) and lower for U_citrateV (164±42 vs. 187±40 mg, respectively, p<0.01). A generalized linear model for repeated measures, adjusted for time, showed that U_citrateV was a predictor of H⁺ retention overall (p<0.01) and within each of the 3 groups (p<0.05).

Conclusion

U_citrateV non-invasively identifies changes in H⁺ retention over time in CKD 2 patients without metabolic acidosis. It should be further explored to follow clinical effectiveness of dietary H⁺ reduction in CKD patients without metabolic acidosis.