Performance of Predictive Equations and Biochemical Measures Quantifying Net Endogenous Acid Production and the Potential Renal Acid Load

Introduction: A limited number of studies have assessed the accuracy and precision of methods for determining the net endogenous acid production (NEAP) and its components. We aimed to investigate the performance of methods quantifying the diet dependent acid-base load. Methods: Data from metabolic balance studies enabled calculations of NEAP according to the biochemical measures (of net acid excretion [NAE], urinary net endogenous acid production [UNEAP], and urinary potential renal acid load [UPRAL]) as well as estimative diet equations (by Frassetto et al., Remer and Manz, Sebastian et al., and Lemann) that were compared among themselves in healthy participants fed both acid and base forming diets for 6 days each. Results: Seventeen participants (mean +/- SD age, 60 +/- 8 years; bodymass index, 23 +/- 2 kg/m(2)) provided 102 twenty-four-hour urine samples for analysis (NAE, 39 +/- 38 mEq/d [range, -9 to 95 mEq/d]). Bland-Altman analysis comparing UNEAP to NAE showed good accuracy (bias, -2 mEq/d [95% confidence interval {CI}, -8 to 3]) and modest precision (limits of agreement, -32 to 28 mEq/d). Accurate diet equations included potential renal acid load (PRAL) by Sebastian et al. (bias, -4 mEq/d [95% CI, -8 to 0]) as well as NEAP by Lemann et al. (bias, 4 mEq/d [95% CI, -1 to 9]) and Remer and Manz (bias, -1 mEq/d [95% CI, -6 to 3]). Conclusions: Researchers are encouraged to collect measures of UPRAL and UNEAP; however, investigators drawing conclusions between the diet-dependent acid-base load and human health should consider the limitations within all methods.