Corrected sodium calculator

Why correct sodium for glucose?

High blood glucose draws water out of cells and dilutes the sodium in the blood. The corrected value estimates what the sodium would be at a normal glucose.

What is the Katz correction?

Add 1.6 mEq/L for every 100 mg/dL of glucose above 100 (Katz, 1973). The Merck Manual uses the same 1.6 factor.

What is the Hillier correction?

A 1999 study by Hillier and colleagues found an average of 2.4 mEq/L per 100 mg/dL; it noted that 1.6 works up to a glucose of about 400 mg/dL and a larger factor fits better above that.

Example

Sodium 130 with glucose 600 mg/dL: Katz 130 + 1.6 × 5 = 138; Hillier 130 + 2.4 × 5 = 142 mEq/L.

Can I enter glucose in mmol/L?

Yes — choose mmol/L; the calculator converts with 1 mmol/L of glucose = 18.016 mg/dL.

How is the corrected sodium calculated, step by step?

Corrected sodium = measured sodium + factor × (glucose − 100) ÷ 100, with sodium in mEq/L, glucose in mg/dL and a factor of 1.6 (Katz) or 2.4 (Hillier). Subtract 100 from the glucose, divide by 100 to count how many 100 mg/dL steps there are above normal, multiply by the factor, and add the result to the measured sodium. At a glucose of 100 mg/dL or below there is nothing to correct, so the calculator returns the measured sodium unchanged. The correction is an estimate of what sodium would read at a normal glucose; the measured value stays what it is.

Worked example: sodium 128 with glucose 400 mg/dL

The glucose is 300 mg/dL above 100, which is 3 steps of 100. With the Katz factor, 128 + 1.6 × 3 = 132.8 mEq/L. With the Hillier factor, 128 + 2.4 × 3 = 135.2 mEq/L. The two answers differ by 2.4 mEq/L, and the difference grows as glucose rises. Hillier and colleagues found that 1.6 fits up to about 400 mg/dL and that a larger factor fits better above it.

Does correcting sodium make a difference in practice?

A 2026 study in PLoS One analyzed 297,714 paired sodium and glucose results from 9,863 critically ill patients in Sweden. Without a correction for high glucose, the Katz formula would have missed 5.1% and the Hillier formula 9.0% of the 602 patients whose sodium shifted by more than 8 mmol/L in 24 hours. Correcting sodium did not change the adjusted ICU mortality. So the correction helps to interpret a result, but it is a bedside estimate, not a treatment target.

Common mistakes with corrected sodium

Entering glucose in the wrong unit: a glucose of 25 mmol/L typed into the mg/dL box is below 100, so a sodium of 130 comes back as 130.0 with no correction, whereas the correct 450 mg/dL gives 135.6 with the Katz factor. Correcting a normal glucose, which changes nothing. Treating the corrected value as the lab’s result: it is a calculation, and the measured sodium is what was actually found. Quoting one factor as exact: the two published factors differ and neither is a precise rule for an individual. Any decision about treatment belongs to a clinician.

Sources and related calculators

Sources: M. A. Katz, “Hyperglycemia-induced hyponatremia: calculation of expected serum sodium depression,” New England Journal of Medicine (1973); T. A. Hillier et al., American Journal of Medicine (1999); “Mathematical analysis of the relationship between glucose and sodium in a large Swedish cohort of critically ill patients,” PLoS One (2026); Merck Manual. Related: serum osmolality calculator, anion gap calculator and corrected calcium calculator.

For general information only — not medical advice. Talk with your doctor or another health professional about your own health. How we check our calculators.