A REEVALUATION OF THE URINARY PARAMETERS OF ACID PRODUCTION AND EXCRETION IN PATIENTS WITH CHRONIC RENAL ACIDOSIS

We have studied acid-base balance in 32 patients attending the renal c linic of Mount Sinai Hospital. The parameters of acid-base balance mea sured included acid production measured as urinary sulfate and organic anions, net acid excretion measured as urinary ammonia plus titratabl e acid minus bicarbonate, and net GI absorption of alkali measured by a new method utilizing urinary electrolytes. Net GI absorption of alka li by urinary electrolytes measures alkali addition to the body from t he GI tract as well as from any other sources, including bone. All pat ients had a creatinine clearance less than 80 ml/min and they were div ided into two groups: those with normal serum bicarbonate (Group 1; N = 12) and those with subnormal serum bicarbonate (Group 2; N = 20). Hy drogen ion balance was -0.6 +/- 9 mEq/day in the first group, while th ose in the second group had a hydrogen ion balance of +16 +/- 5 mEq/da y. A group of 8 normal controls had a hydrogen ion balance of -0.3 +/- 5 mEq/day. When the sum of all cations was compared with the sum of a ll anions in the urine, a cation gap of exactly the same magnitude as the positive hydrogen ion balance was found in patients with low serum bicarbonate. In conclusion, our data show that patients with decrease d GFR and low serum bicarbonate appear to have a significantly positiv e hydrogen ion balance. However, we believe that the positive hydrogen ion balance is only apparent, but not real for the following reasons. If the positive hydrogen balance shown by the previous investigators were due to bone buffering, the positive balance should have disappear ed in our study since we included the contribution of bone buffers in the calculation of acid-base balance. Moreover, the positive hydrogen ion balance in our study would indicate the presence of a cation gap, a theoretical impossibility. The most likely explanation for the appar ently positive hydrogen ion balance, shown only in the low bicarbonate group, is a systematic technical error in the current methods for mea surement of parameters of acid-base balance, either an underestimation of net acid excretion or an overestimation of acid production. Furthe r studies are needed to delineate the sources of technical errors.