Renal & electrolytes

Corrected sodium calculator

Q: Which correction factor does this use — 1.6 or 2.4?

The Hillier 1999 factor: 2.4 mmol/L of sodium per 5.6 mmol/L of glucose above 5.6. The older Katz factor of 1.6 underestimates the correction at high glucose, which is precisely where the answer matters most.

Q: What does a high corrected sodium mean in HHS?

An underlying water deficit: once the glucose dilution is accounted for, a high corrected sodium signals substantial free-water depletion — common in HHS — and free-water replacement belongs in the fluid plan.

Q: What if the sodium is still low after correction?

Then the hyponatraemia is real, not dilutional — investigate beyond the glucose for the usual causes rather than assuming the hyperglycaemia explains it.

In DKA a 'low' sodium is often just dilution — correct for the glucose before you treat the number.

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Measured sodium

mmol/L

Glucose

mmol/L

Corrected Na = measured Na + 2.4 mmol/L per 5.6 mmol/L glucose above 5.6.Reference: Hillier et al. 1999 (2.4 factor; the older Katz factor is 1.6).

How to read the result

Corrected sodium (mmol/L) falls into these published bands.

< 135.0Low once correctedTrue hyponatraemia — investigate beyond the glucose.

135.0 – 145.9Normal once correctedThe measured dilution is explained by glucose; expect sodium to rise as glucose falls.

≥ 146.0High once correctedUnderlying water deficit — common in HHS; plan free-water replacement.

Worked example

A patient in DKA with a measured sodium of 126 mmol/L and a glucose of 40 mmol/L.

Corrected sodium 140.7 mmol/L — normal once corrected

The measured hyponatraemia is entirely dilutional, explained by the glucose: expect the sodium to rise as the glucose falls, and resist treating a low number that is not truly low.

Who this is for

For clinicians managing diabetic ketoacidosis and hyperosmolar hyperglycaemic state, where glucose draws water into the vascular space and dilutes the measured sodium. The corrected value shows whether the hyponatraemia is real — and in HHS, a normal or high corrected sodium exposes the substantial free-water deficit that shapes the fluid plan.

How it works

What it calculates

The sodium concentration expected once an elevated glucose is corrected — glucose draws water into the vascular space and dilutes the measured sodium.

When to use it

DKA and HHS. A 'low' sodium with glucose of 40 mmol/L may be entirely dilutional; a normal or high corrected sodium in HHS signals a substantial free-water deficit that shapes the fluid plan.

The formula

Adds 2.4 mmol/L of sodium per 5.6 mmol/L of glucose above normal (Hillier 1999); the older Katz factor of 1.6 underestimates the correction at high glucose.

Built on published evidence

Hillier et al. 1999 (2.4 factor; the older Katz factor is 1.6)

Codification last reviewed 2026-08-28, and checked against published reference values in automated tests on every release — see the full evidence ledger.

Questions clinicians ask

Which correction factor does this use — 1.6 or 2.4?

The Hillier 1999 factor: 2.4 mmol/L of sodium per 5.6 mmol/L of glucose above 5.6. The older Katz factor of 1.6 underestimates the correction at high glucose, which is precisely where the answer matters most.

What does a high corrected sodium mean in HHS?

An underlying water deficit: once the glucose dilution is accounted for, a high corrected sodium signals substantial free-water depletion — common in HHS — and free-water replacement belongs in the fluid plan.

What if the sodium is still low after correction?

Then the hyponatraemia is real, not dilutional — investigate beyond the glucose for the usual causes rather than assuming the hyperglycaemia explains it.

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