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Abstract: SA-PO981

Urine Excretion of Citrate and Ammonium to Non-Invasively Identify Eubicarbonatemic Acidosis in Patients With CKD

Session Information

  • CKD: Pathobiology - II
    November 05, 2022 | Location: Exhibit Hall, Orange County Convention Center‚ West Building
    Abstract Time: 10:00 AM - 12:00 PM

Category: CKD (Non-Dialysis)

  • 2203 CKD (Non-Dialysis): Mechanisms

Authors

  • Goraya, Nimrit, Baylor Scott and White Central Texas, Temple, Texas, United States
  • Madias, Nicolaos E., Tufts University School of Medicine, Boston, Massachusetts, United States
  • Mamun, Abdullah A., Baylor Scott and White North Texas, Dallas, Texas, United States
  • Simoni, Jan, Texas Tech University System, Lubbock, Texas, United States
  • Wesson, Donald E., The University of Texas at Austin Dell Medical School, Austin, Texas, United States
Background

Increasing acid (H+) retention while plasma total CO2 (PTCO2) remained normal (eubicarbonatemic acidosis) during chronic kidney disease (CKD) progression was associated with decreasing urine citrate excretion (UcitV) . Increasing positive H+ balance while PTCO2 remained normal in patients with CKD progression was associated with decreased urine ammonium excretion (UNH4+V). We explored if the combination of UcitV and UNH4+V, than either alone, better identified H+ retention, in patients with CKD and eubicarbonatemic acidosis.

Methods

We recruited 313 macroalbuminuric, non-diabetic participants with eGFR [mean (SD), ml/min/1.73 m2] for CKD 1 [n=62, 99.2 (7.3)], CKD 2 (n=167, 73.8 (6.3), and CKD 3 (n=84, 39.9 (6.7)] without metabolic acidosis (PTCO2 ≥ 22 mM). We assessed H+ retention by comparing observed to expected increase in PTCO2 in response to retained HCO3 (dose-urine excretion) 2 hours after an oral NaHCO3 bolus (0.5 mEq/Kg bw), assuming 50% body weight HCO3 space of distribution. We compared 8-hour UcitV (8h UcitV) and UNH4+V (8h UNH4+V) across groups and performed linear regressions (LR) with H+ retention within groups.

Results

With advancing CKD, H+ retention [mean (SD), mmol)] progressively increased [CKD 1= 3.8 (12.5), CKD 2=18.2 (12.4), CKD 3=25.6 (9.0), p<0.01)]. With advancing CKD, 8h UcitV (mmol/8h) progressively decreased [CKD 1=1.14 (0.03), CKD 2=1.00 (0.22), CKD 3=0.87 (0.9), p<0.01)]. By contrast, 8h UNH4+V (mEq/8h) was not different between CKD 2 vs. CKD 1 [14.1 (2.6) vs.14.7 (2.5), respectively, p=0.24)] but was lower in CKD 3 [13.0 (2.3] than either CKD 2 or CKD 1 (p<0.01). LR for UcitV vs. H+ retention was negative for both CKD 2 (p<0.01, r2=0.61) and CKD 3 (p<0.01, r2=0.75) but was not significant for CKD 1 (p=0.50, r2=0.04). LR for UNH4+V vs. H+ retention was positive for CKD 2 (p<0.04, r2=0.05) and negative for CKD 3 (p<0.01, r2=0.80) but not significant for CKD 1 (p=0.14, r2=0.05). Adding UNH4+V to UcitV in the regression increased r2 marginally for CKD 2 (0.61 to 0.63) and CKD 3 (0.75 to 0.79).

Conclusion

The data show that lower UcitV identified higher H+ retention in eubicarbonatemic patients with CKD 2 or CKD 3 but the UNH4+V vs. H+ retention relationship diverged between CKD 2 and CKD 3. Adding UNH4+V to UcitV marginally enhanced its predictive power.