Your corrected sodium value estimates what the serum sodium concentration would be if the blood glucose were at a normal level of 100 mg/dL. If the corrected sodium is within the normal range (135-145 mEq/L), the measured hyponatremia is entirely attributable to the dilutional effect of hyperglycemia, and sodium is expected to normalize as glucose is corrected. If the corrected sodium remains low (below 135 mEq/L), there is a true underlying hyponatremia that needs to be evaluated independently.

Conversely, if the corrected sodium is elevated (above 145 mEq/L), the patient has underlying hypernatremia masked by the dilutional effect of high glucose. This is particularly important in DKA and HHS management because as insulin lowers glucose, water shifts back into cells, and the serum sodium will rise. Failure to recognize underlying hypernatremia can lead to overly rapid sodium changes and risk of osmotic demyelination or cerebral edema.

Use this calculator whenever a patient presents with hyperglycemia (glucose above 100 mg/dL) and an abnormal sodium level, particularly in diabetic ketoacidosis (DKA), hyperosmolar hyperglycemic state (HHS), and other severe hyperglycemic emergencies. It is essential for accurately assessing a patient's true sodium status before and during insulin therapy.

It is also valuable for monitoring sodium trends during DKA or HHS treatment. As glucose falls with insulin therapy, you can predict how sodium will change. If the corrected sodium is stable or rising appropriately, fluid management is on track. If the corrected sodium is falling, the patient may be receiving excessive free water.

The Katz correction factor of 1.6 mEq/L per 100 mg/dL glucose elevation was derived from theoretical modeling and small studies. Some evidence (Hillier 1999) suggests that 2.4 mEq/L per 100 mg/dL is more accurate at glucose levels above 400 mg/dL. Neither correction factor has been rigorously validated in large prospective studies.

The formula assumes a linear relationship between glucose and sodium displacement, which may not hold at extreme glucose levels (above 800-1000 mg/dL). It also does not account for other causes of pseudohyponatremia (such as severe hyperlipidemia or hyperproteinemia) or for concurrent osmotically active substances. In clinical practice, the corrected sodium should be used as a guide alongside serum osmolality, clinical assessment of volume status, and serial monitoring rather than as a standalone decision point.