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Abstract: FR-PO627

Urinary Net Endogenous Acid Production: A Reliable Predictor of Net Acid Excretion

Session Information

Category: Fluid and Electrolytes

  • 902 Fluid and Electrolytes: Clinical


  • Banerjee, Tanushree, San Francisco General Hospital, San Francisco, California, United States
  • Frassetto, Lynda A., University of California San Francisco, San Francisco, California, United States

High acid production and positive acid balance have been associated with progression of chronic kidney disease (CKD) and degenerative aging processes. Endogenous acid production (EAP) equations that most accurately represent net acid excretion (NAE) require analyses of diet and stool unmeasured anions and a research lab to measure titratable acids and bicarbonate, a somewhat complicated research protocol. Being able to evaluate only urinary analytes might be easier. Here, we evaluate the predictive value of urinary measured (EAP) and unmeasured anions (UNEAP) to the measured value of NAE.


24 hour urine collections from metabolic balance studies from 15 patients for repeated intervals were performed at the control period (baseline), diet intervention phase, and the recovery phase. Each phase was at least 3 days. NAE was calculated from measured values (= titratable acid + ammonium – bicarbonate). UNEAP was calculated from urinary [(phosphate+chloride)-(sodium+potassium+calcium)] + sulfate (SO4) + total organic acid (OA) production. EAP = urinary SO4+ OA salts. We used mixed effects model with repeated measures to assess agreement between the estimated and measured value of NAE.


Assessment between these measures showed a high correlation between UNEAP and NAE (r=0.85, p<0.001). EAP underestimated the measured value of NAE by 9.7 mEq/d and the difference in the means was statistically significant (p=0.003) with the 95% limits of agreement between the differences being -32.5 mEq/d to 12.9 mEq/d. On the other hand, there was a non-significant difference in the means (3.24 mEq/d) between UNEAP and NAE with the 95% limits of agreement being -25.5 mEq/d to 32.0 mEq/d.


Using only urine measures, UNEAP was a more reliable estimate of NAE compared to EAP. Measures for estimating UNEAP may be less cumbersome than measuring NAE and help promote research into treatments that affect acid balance, such as alkali treatment for CKD.


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