Corrected Sodium Calculator

Corrected Sodium in Hyperglycemia

The serum sodium (Na) result may be altered by pre-existing high glucose levels in patients with hyperglycemia. In the presence of abnormally high blood glucose levels, if there is no change in the total body water the observed low sodium levels are likely due to the hyponatremic response and should not be confused with established hyponatremia.

Sodium levels must be corrected before interpretation, via:

• Sodium Correction (Katz, 1973) = Measured sodium in mEq/L + 0.016 x (Serum glucose in mg/dL - 100)

In 1999, Hillier et al. updated the original formula by Katz, observing the need for a higher correction factor, especially in serum glucose levels greater than 400 mg/dL.

• Sodium Correction (Hillier, 1999) = Measured sodium in mEq/L + 0.024 x (Serum glucose in mg/dL - 100)

The physiological mechanism behind the apparent hyponatremia can be summarized with the following three steps:

1. When glucose levels increase abnormally, extra cellular fluid osmolality rises above that of intracellular fluid;
2. This leads to glucose entering the cell and displacing water back in the extracellular space;
3. The cell is thus depleted of cellular water and the serum Na concentration falls in proportion to the extra cellular fluid dilution.

Serum sodium correction is calculated via a correction factor of 2.4mEq/L or 1.6 mEq/L, for every 100 mg/dL increase in plasma glucose levels above normal, to reflect the real natremia situation in the body.

Once serum glucose levels return to normal (either via natural insulin mechanism or by administration of external insulin), serum sodium levels also return to normal, without the need for sodium correction infusate, as would have been the case if the hyponatremia was established, not just temporary and linked to hyperglicemia.

References

Original reference

Katz MA. Hyperglycemia-induced hyponatremia--calculation of expected serum sodium depression. N Engl J Med. 1973; 18;289(16):843-4.

Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. Am J Med. 1999; 106(4):399-403.

Other references

Hoorn EJ, et al. Hyponatremia and mortality: moving beyond associations. Am J Kidney Dis. 2013; 62(1):139–149.

Pfennig CL, et al. Sodium disorders in the emergency department: a review of hyponatremia and hypernatremia. Emerg Med Pract. 2012; 14(10):1–26.