Medical AISodium correction for hyperglycaemia
High glucose pulls water out of cells into plasma, diluting the measured sodium so it reads lower than the patient's true sodium status. Correcting for glucose estimates the sodium that would be seen at a normal glucose. This tool reports the correction with both the original Katz factor (1.6 per 100 mg/dL above 100) and the later Hillier factor (2.4 per 100 mg/dL above 100); the headline value uses 2.4.
How to measure each input
- Glucose unit
- Enter glucose in mg/dL. If your laboratory reports mmol/L, multiply by 18 first (for example 33.3 mmol/L equals about 600 mg/dL).
- Choosing a factor
- Katz (1973) derived 1.6 mmol/L per 100 mg/dL; Hillier (1999) found the empirical average closer to 2.4 and recommended it as the better overall estimate. This tool shows both so you can see the spread.
- Very high glucose
- Hillier noted the relationship is steeper above 400 mg/dL (closer to a factor of 4). At extreme glucose levels treat the correction as an approximation and re-check sodium as glucose falls.
Interpretation
| Band | Meaning |
|---|---|
| Corrected Na < 135 mmol/L, true hyponatraemia | Even after correcting for glucose the sodium is low, so there is genuine hyponatraemia on top of the hyperglycaemia. Look for additional causes (fluid shifts, vomiting, thiazides, SIADH) and manage accordingly. |
| Corrected Na 135 to 145 mmol/L, normal | The corrected sodium is within the normal range, so the low measured value reflects glucose-driven dilution (pseudohyponatraemia) rather than true sodium depletion. Sodium should normalise as glucose is treated. |
| Corrected Na > 145 mmol/L, true hypernatraemia | The corrected sodium is high, indicating a real free-water deficit masked by the diluting effect of hyperglycaemia, as is often seen in hyperosmolar hyperglycaemic state. Account for this when planning fluid and free-water replacement. |
Pitfalls, exclusions and caveats
- The choice of factor changes the answer: at a glucose of 600 mg/dL the 1.6 and 2.4 factors differ by about 4 mmol/L in the corrected sodium. State which factor you used.
- Correction is mainly relevant in marked hyperglycaemia such as diabetic ketoacidosis (DKA) and hyperosmolar hyperglycaemic state (HHS); at near-normal glucose the adjustment is trivial.
- Do not over-correct sodium: the corrected value guides interpretation of true sodium status, but the actual rate of sodium change during treatment must still be limited to avoid osmotic demyelination.
- Relationship is non-linear at very high glucose (Hillier suggested a steeper factor above 400 mg/dL), so a single linear factor only approximates the shift.
- This corrects only for glucose. Other causes of spurious sodium (severe hyperlipidaemia or hyperproteinaemia causing true pseudohyponatraemia by the indirect method) are not addressed here.
Corrected Na = Measured Na + factor x ((Glucose - 100) / 100), with glucose in mg/dL. Headline uses factor 2.4 (Hillier 1999); secondary uses 1.6 (Katz 1973). No correction is applied when glucose is at or below 100 mg/dL.Frequently asked
Should I use the 1.6 or the 2.4 correction factor?
Katz (1973) derived 1.6 mmol/L per 100 mg/dL of glucose, and this is the classic teaching value. Hillier et al. (1999) measured the average decrease at about 2.4 and recommended it as the better overall estimate, especially at higher glucose levels. This calculator shows both; the headline value uses 2.4. The key is to be consistent and to state which factor you applied.
Why does sodium read low when glucose is high?
Glucose is osmotically active and stays largely outside cells, so a high glucose draws water from the intracellular space into the plasma. That extra water dilutes the sodium, lowering the measured value without any change in total body sodium. Correcting for glucose estimates the sodium once that dilution is removed.
Does a normal corrected sodium mean nothing is wrong?
It means the low measured sodium is explained by hyperglycaemia rather than true sodium loss, so it should normalise as glucose is treated. A corrected sodium that is still low signals additional, genuine hyponatraemia, and a high corrected sodium signals a free-water deficit, as commonly seen in hyperosmolar hyperglycaemic state.
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