Serum sodium correction tools
Serum sodium correction estimates what the sodium concentration would be after accounting for the dilutional effect of hyperglycemia. A serum sodium correction calculator is useful because high glucose pulls water from cells into the extracellular fluid, which can make measured sodium appear lower than the underlying water-balance state.
The corrected value does not replace the measured laboratory value. Instead, it helps interpret whether apparent hyponatremia is partly explained by glucose-driven water movement and whether the corrected sodium falls in a low, normal, or high sodium range.
Core formulas
In conventional units, glucose is entered in mg/dL. The correction is usually applied only to glucose above 100 mg/dL:
\[
\begin{aligned}
\mathrm{Na^+_{corrected}}
&= \mathrm{Na^+_{measured}}
+ \text{factor}\cdot
\frac{\text{glucose} - 100}{100}
\end{aligned}
\]
In SI units, glucose is entered in mmol/L. The same relationship is expressed using the approximate SI equivalent of a 100 mg/dL glucose rise:
\[
\begin{aligned}
\mathrm{Na^+_{corrected}}
&= \mathrm{Na^+_{measured}}
+ \text{factor}\cdot
\frac{\text{glucose} - 5.6}{5.55}
\end{aligned}
\]
The correction factor is commonly selected as 1.6 or 2.4 mmol/L per 100 mg/dL glucose increase, depending on the teaching formula used. If glucose is not above the reference baseline, the correction is treated as zero in this calculator model.
How to interpret corrected sodium
If corrected sodium is much higher than measured sodium, the measured value is likely being diluted by hyperglycemia. This means the true water-balance pattern may be less hyponatremic than the measured sodium first suggests. If corrected sodium remains low, then hyperglycemia explains only part of the low sodium pattern.
A corrected value in the normal range suggests that the low measured sodium may be largely dilutional. A corrected value above the normal range suggests a more concentrated water-balance state that may be hidden by the measured sodium value.
- Do not mix mg/dL glucose with the SI correction formula.
- Use the same correction factor consistently when comparing cases.
- Do not apply a hyperglycemia correction when glucose is below the baseline.
- Interpret corrected sodium together with osmolality, volume status, and clinical context.
Micro example: If measured sodium is 125 mmol/L, glucose is 700 mg/dL, and the correction factor is 2.4, glucose is 600 mg/dL above baseline. The correction is 14.4 mmol/L, giving a corrected sodium of about 139.4 mmol/L.
This tool is best used for learning dilutional hyponatremia patterns in hyperglycemia and comparing measured versus corrected sodium. For a broader fluid and electrolyte interpretation, the next step is to connect corrected sodium with plasma osmolality, free water balance, and acid-base status.
