Updated Review of Sodium Correction for Hyperglycemia

Hyponatremia is a disorder of decreased tonicity, which generally results from water excess and has important treatment considerations given the effects of altered hypotonicity on the brain. However, in patients with hyperglycemia, measured serum sodium levels can be low despite no decrease in tonicity. This is due to osmotic water shifts from the intracellular to extracellular compartment resulting in hyponatremia. Distinguishing between true and dilutional hyponatremia is imperative for clinical decision making and to guide treatment strategies. To guide management decisions such as choice of fluids, in the presence of hyperglycemia, a correction factor is generally applied to calculate “corrected sodium,” defined here as serum sodium adjusted for hyperglycemia. There is a non-linear relationship between decrease in serum sodium with hyperglycemia and, depending on serum glucose, the corrected sodium ranges from 1.6 mEq/L to 4.0 mEq/L sodium increase for every 100 mg/dL rise in serum glucose. Clinicians should act on the corrected sodium level, not the unadjusted measurement. In fact, studies show that in cases of hyponatremia with concurrent severe hyperglycemia, the true tonicity disorder is often hypertonicity rather than hypotonicity. Moreover, outcomes tend to correlate with corrected rather than measured serum sodium. Finally, as in all disorders of plasma tonicity, frequent monitoring of sodium levels and in cases of hyperglycemia correction for resulting hyperosmolality, is essential as tonicity can fluctuate rapidly with management.