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Am J Physiol Renal Physiol. 2019 Jun 19. doi: 10.1152/ajprenal.00044.2019. [Epub ahead of print]

Urine citrate excretion identifies changes in acid retention as eGFR declines in patients with chronic kidney disease.

Author information

1
Internal Medicine, Baylor Scott and White Health.
2
Surgery, Texas Tech University HSC, United States.
3
Biostatistics, Baylor Scott and White Health.
4
Biostatistics, Baylor Scott and White Health and Wellness Center, United States.
5
St. Elizabeth's.
6
Internal Medicine, Baylor Scott and White Health, United States.

Abstract

We examined as secondary analysis if increased acid (H+) retention occurring as eGFR decreases in patients with chronic kidney disease (CKD) stage 2 eGFR (60-89 ml.min-1.73m-2) (CKD 2) without metabolic acidosis and followed over ten years is predicted by changes in 8 hour urine citrate excretion (UcitrateV). We randomized 120 CKD 2 non-diabetic, hypertension-associated nephropathy patients with plasma total CO2 (PTCO2) > 24 mM to receive 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). We assessed eGFR (CKD-EPI) and H+ retention by comparing observed to expected PTCO2 increase 2 hours after oral NaHCO3 bolus (0.5 mEq/kg bw). Although 10-year vs. baseline eGFR was lower for each group, 10-year eGFR was higher (p<0.01) in HCO3- (59.6±4.8 ml.min-1.73m-2) than NaCl and UC (52.1±5.9 and 52.3±4.1 ml.min-1.73m-2, respectively). Less eGFR preservation was associated with higher 10-year vs. baseline H+ retention in NaCl (26.5±13.1 vs. 18.2±15.3 mmol, p<0.01) and UC (24.8±11.3 vs. 17.7±10.9 mmol, p<0.01) and with lower 10-year vs. baseline UcitrateV for NaCl (162±47 vs. 196±52 mg, respectively, p<0.01) and UC (153±41 vs. 186±42 mg, respectively, p<0.01). Conversely, better eGFR preservation in HCO3- was associated with no differences in 10-year vs. baseline H+ retention (14.2±13.5 vs. 16.1±15.1 mmol, p=1.00) or UcitrateV (212±45 vs. 203±49 mg, respectively, p=0.74). An overall generalized linear model for repeated measures showed that UcitrateV predicted H+ retention (p<0.01). Less eGFR preservation in CKD 2 patients without metabolic acidosis was associated with increased H+ retention that was predicted by decreased UcitrateV.

KEYWORDS:

acid retention; acidosis; bicarbonate; chronic kidney disease; glomerular filtration rate

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