Metabolic acidosis in advanced renal failure: Differences between diabeticand nondiabetic patients

Metabolic acidosis is almost invariably a consequence of advanced renal fai lure, although its severity can vary widely. To evaluate the determinants o f the severity of metabolic acidosis, with special interest in determining if there is any difference in the prevalence and severity of metabolic acid osis between patients with and without diabetes, 113 predialysis patients w ith renal failure were studied, Criteria for inclusion onto the study were: creatinine clearance (Ccr)/1.73 m(2) less than 30 mL/min, no alkali therap y within the previous 30 days, and the absence of respiratory diseases. For ty-eight patients had diabetes (33 patients with diabetic nephropathy). The following data were analyzed: demographics; cause of renal failure; hemato crit; serum urea, creatinine, uric acid, albumin, glucose, hemoglobin Al,, bicarbonate, sodium, potassium, chloride, calcium, phosphorus, and alkaline phosphatase levels; anion gap; urinary protein excretion; Ccr/1.73 m(2); h alf of the sum of creatinine and urea clearances (Ccr-Cu); protein-equivale nt nitrogen appearance (PNA); and whether the patients received diuretics ( 75 patients), angiotensin-converting enzyme inhibitors (54 patients), and/o r calcium channel blockers (55 patients), After the exclusion of eight pati ents because of hypochloremia (three patients with and five patients withou t diabetes), mean serum bicarbonate levels were significantly greater in pa tients with diabetes than in the rest of the patients (20.7 +/- 2.3 v 18.2 +/- 2.3 mmol/L; P = 0.0001), The mean anion gap (mmol/L) was also significa ntly less in patients with than without diabetes (19.70 +/- 3.65 v 22.35 +/ - 3.64; P = 0.003). Eleven of 105 patients had serum bicarbonate levels of 23 mmol/L or greater (9 patients with and 2 patients without diabetes), Pur e elevated anion gap followed by mixed (high anion gap and hyperchloremia) were the most common types of metabolic acidosis observed in both groups. T here were no differences in PNA, diuretic treatment, or vomiting history be tween patients with and without diabetes. By multiple logistic regression a nalysis, the best determinants for a serum bicarbonate level greater than 1 9 mmol/L were: the diagnosis of diabetic nephropathy (odds ratio, 0.107; P = 0.0002), Ccr Cu (odds ratio, 0.824; P = 0.014), and age (odds ratio, 0.96 6; P = 0.046), In conclusion, patients with diabetes with advanced renal fa ilure showed a less severe metabolic acidosis, which cannot be explained by gastrointestinal hydrogen ion losses, drugs, or reduced protein catabolic rate. Patients with diabetes may have a more efficient extrarenal generatio n of bicarbonate than end-stage renal failure patients without diabetes. (C ) 1999 by the National Kidney Foundation, Inc.