Why does high glucose lower measured sodium?

Hyperglycaemia draws water out of cells into the extracellular space, diluting the serum sodium. This produces a translocational, dilutional hyponatraemia, so the measured sodium underestimates the body's true sodium status until the glucose is accounted for.

What is the difference between the Katz and Hillier formulas?

Katz adds 1.6 mmol/L to sodium for every 5.6 mmol/L (100 mg/dL) of glucose above normal, while Hillier adds 2.4 mmol/L. Hillier was derived experimentally and is more accurate at very high glucose levels, whereas Katz is the traditional bedside rule.

What glucose value is used as the baseline?

The correction is applied to the glucose above a normal reference of about 5.6 mmol/L (100 mg/dL). The formula multiplies the correction factor by the number of 5.6 mmol/L increments by which glucose exceeds this baseline, then adds the result to measured sodium.

Does corrected sodium change my fluid management?

It can. A normal or high corrected sodium during hyperglycaemia suggests significant free-water loss and may favour more hypotonic fluid once glucose is controlled, while a low corrected sodium indicates true sodium depletion. Always follow your local DKA/HHS protocol.

Corrected Sodium for Hyperglycaemia

Q: When should I correct the sodium?

Correct the sodium whenever the blood glucose is significantly elevated, classically in diabetic ketoacidosis (DKA) and the hyperosmolar hyperglycaemic state (HHS). It guides fluid choice and helps avoid over-treating an apparent hyponatraemia that will resolve as glucose falls.

What corrected sodium means

In hyperglycaemia, a high blood glucose pulls water from inside cells into the bloodstream, diluting serum sodium and creating an artefactually low reading. This is translocational (dilutional) hyponatraemia. Correcting the sodium for glucose reveals the patient’s true sodium status, which is essential for safe fluid management in diabetic ketoacidosis (DKA) and the hyperosmolar hyperglycaemic state (HHS).

How it works

Both common formulas add sodium back in proportion to how far glucose exceeds the normal baseline of 5.6 mmol/L (100 mg/dL):

Corrected Na = Measured Na + factor × (Glucose − 5.6) / 5.6

Katz (1973): factor = 1.6 — the classic bedside correction.
Hillier (1999): factor = 2.4 — experimentally derived and more accurate at very high glucose.

If glucose is entered in mg/dL it is converted to mmol/L by dividing by 18 before the formula is applied. When glucose is at or below the baseline, no correction is added.

Tips and example

A patient in DKA with a measured sodium of 130 mmol/L and glucose of 33.6 mmol/L has, using Katz: corrected Na = 130 + 1.6 × (33.6 − 5.6) / 5.6 = 130 + 8 = 138 mmol/L — a normal true sodium despite the apparently low measured value. Using the Hillier factor gives 130 + 12 = 142 mmol/L. Choose the formula your unit uses, and always interpret the result within your DKA/HHS protocol and overall clinical picture.