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.

What is the Corrected Sodium for Hyperglycaemia?

Use the Katz or Hillier correction formula to calculate true serum sodium in the presence of hyperglycaemia, preventing misinterpretation of apparent hyponatraemia. Essential in the assessment of DKA and hyperosmolar hyperglycaemic state. It runs free in your browser on Gera Tools, with nothing uploaded.

Corrected Sodium for Hyperglycaemia

Name: Corrected Sodium for Hyperglycaemia
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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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.

Worked example

A patient in DKA presents with a measured sodium of 130 mmol/L and a blood glucose of 33.6 mmol/L.

Glucose excess = 33.6 − 5.6 = 28.0 mmol/L
Number of 5.6 increments = 28.0 / 5.6 = 5.0

Katz correction:    130 + 1.6 × 5.0 = 130 + 8  = 138 mmol/L
Hillier correction: 130 + 2.4 × 5.0 = 130 + 12 = 142 mmol/L

The measured sodium of 130 mmol/L looks hyponatraemic, but the corrected sodium is 138–142 mmol/L — normal or slightly high, indicating the patient has significant free-water deficit despite the low raw value.

Clinical interpretation: what the corrected sodium tells you

The corrected sodium in DKA and HHS guides fluid choice, not just classification:

Corrected sodium low (below ~135 mmol/L): True sodium depletion is present alongside the water shift. Initial fluid resuscitation with normal saline is generally appropriate to correct both volume and sodium.
Corrected sodium normal (~135–145 mmol/L): The hyponatraemia is mainly from glucose dilution. As glucose falls with treatment, the measured sodium should rise toward the corrected value. Monitor closely to avoid hypernatraemia developing during treatment.
Corrected sodium high (above ~145 mmol/L): Significant free-water deficit. This pattern is more typical of HHS than DKA. Fluid management needs to consider tonicity carefully; more hypotonic fluid may be appropriate once initial volume is restored.

Local DKA and HHS protocols specify exact fluid strategies — the corrected sodium informs the decision, not substitutes for the protocol.

Katz vs Hillier: which to use

The Katz factor of 1.6 has been the bedside standard since the 1970s and is widely cited in clinical guidelines. Hillier’s factor of 2.4 was derived experimentally by inducing hyperglycaemia in volunteers and found to more accurately reflect sodium changes at very high glucose concentrations. Some institutions have moved to using Hillier routinely; others retain Katz. In practice, the difference becomes clinically significant mainly at very high glucose (above about 20–25 mmol/L / 360–450 mg/dL). Use whichever factor your local protocol specifies, and note which you used when documenting the result.