ESTIMATES OF INTERDIALYTIC SODIUM AND WATER-INTAKE BASED ON THE BALANCE PRINCIPLE - DIFFERENCES BETWEEN NONDIABETIC AND DIABETIC SUBJECTS ON HEMODIALYSIS

Whether salt or water intake is the primary cause of interdialytic wei ght gain (Delta W) has important implication for the design of measure s to prevent large Delta W. In 17 hemodialysis patients dialyzed again st a bath containing 140 mmol/L of sodium, monthly predialysis serum s odium was compared with post dialysis serum sodium. A decrease in seru m sodium in the interdialytic period would indicate that primary water consumption accounts for at least part of the Delta W. Interdialytic sodium intake, isotonic fluid gain (Delta W-isotonic) and net pure wat er gain (Delta W-H2O) were calculated by balance formulae. Serum sodiu m concentration was corrected in diabetic subjects to the value corres ponding to euglycemia (100 mg/dl). Estimated interdialytic sodium inta ke was compared with the prescribed sodium intake and, in seven subjec ts, to sodium intake estimated from dietary records. Results for nondi abetic subjects (N = 9): [Na](post) 139.3 +/- 1.9 mmol/L, [Na](pre) 14 0.1 +/- 2.1 mmol/L (NS), Delta W 1.15 +/- 0.55 L/24 hr, Delta W-isoton ic 1.33 +/- 0.57 L/24 hr, Delta W-H2O -0.20 +/- 0.58 L/24 hr, estimate d sodium intake 206 +/- 75 mmol/24 hr, prescribed sodium intake 121 +/ - 29 mmol/24 hr (p = 0.028). Results for diabetic subjects (N = 7): [N a](post) 140.1 +/- 2.5 mmol/L, [Na](pre) 137.7 +/- 3.1 mmol/L (p < 0.0 1), Delta W 1.26 +/- 0.38 L/24 hr, Delta W-isotonic 0.59 +/- 0.63 L/24 br, Delta W-H2O 0.66 +/- 0.39 L/24 hr, estimated sodium intake 160 +/ - 81 mmol/24 hr, prescribed sodium intake 124 +/- 30 mmol/24 hr (NS), glycosylated hemoglobin 9.7 +/- 2.8% (normal, 4.1-5.7%). In seven subj ects, estimates of sodium intake from balance formulae (233 +/- 113 mm ol/24 hr) were not different from estimates from dietary records (212 +/- 87 mmol/24 hr). Sodium intake accounted for all the interdialytic weight gain in nondiabetic subjects. In diabetic patients, only approx imately half of the interdialytic weight gain was accounted for by sod ium intake. The other half was due to pure water gain, probably caused by hyperglycemia.