Sodium Metabolism in Chronic Kidney Disease

Sodium balance is reasonably well maintained in CKD until renal function is seriously diminished. CKD patients do not usually develop either edema or sodium depletion. The adaptive response to decreasing GFR in the face of a constant (or high) sodium diet is an increase in the fractional excretion of sodium (FE_Na). This, in turn, requires a reduction in sodium reabsorption per nephron. In most circumstances, this is protective and prevents or limits sodium retention and extracellular fluid volume expansion. However, if dietary sodium is suddenly or greatly reduced, the kidney cannot immediately adjust. Distal nephron tubular function in CKD is not permanently impaired because the kidney can adequately adjust to decreases in sodium intake if the changes occur slowly. Hypertension is very common in CKD. Control of extracellular fluid volume through diet, and dialysis prescription in the case of ESRD, is the most effective means of controlling blood pressure. The KDOQI Clinical Practice Guidelines recommends that dietary sodium intake be limited to no more than 2.4g/day.