What it is
Hyperglycaemia osmotically draws water from cells into plasma, diluting sodium and producing a dilutional (translocational) hyponatraemia. The corrected sodium estimates what the serum sodium would be at a normal glucose, so you can track true sodium status as glucose falls during DKA treatment. This is a real osmotic shift — distinct from pseudohyponatraemia.
The formula
For each 100 mg/dL of glucose above 100 mg/dL, add a correction factor to the measured sodium:
Corrected Na = measured Na + factor × [(glucose − 100) / 100]
| Factor | Origin | Best for |
|---|---|---|
| 1.6 | Katz (1973), theoretical | Glucose up to ~400 mg/dL |
| 2.4 | Hillier (1999), experimental | Glucose >400 mg/dL |
Worked example — Na 130 mEq/L, glucose 600 mg/dL:
- Excess glucose units = (600 − 100) / 100 = 5
- Factor 1.6: 130 + 1.6 × 5 = 138 mEq/L
- Factor 2.4: 130 + 2.4 × 5 = 142 mEq/L
A “low” measured sodium of 130 is actually normal-to-high once corrected — so the patient is not truly hyponatraemic.
Why the corrected sodium matters in DKA
- Sodium should rise as glucose falls. During fluid and insulin therapy, falling glucose unmasks the true sodium. A corrected sodium that fails to rise (or a measured sodium that does not climb as glucose drops) is a warning sign for excessive free-water administration and cerebral oedema risk — the leading cause of DKA mortality in children.
- It guides fluid tonicity and rate decisions; do not be reassured by a low measured sodium when glucose is very high.
- Effective osmolality (2×Na + glucose/18) and the corrected sodium should be trended together.
1.6 vs 2.4 — which to use
The relationship is non-linear: at very high glucose (>400 mg/dL) the dilution effect is greater, so the 2.4 factor fits better at extremes; 1.6 is the historical default and reasonable in milder hyperglycaemia. The calculator reports both. The clinically important point is the trend, not the single value.
Pseudohyponatraemia — do not confuse it
| Mechanism | Measured osmolality | |
|---|---|---|
| Hyperglycaemic (true dilutional) | Osmotic water shift into plasma | High |
| Pseudohyponatraemia | Lab artefact from severe hyperlipidaemia/hyperproteinaemia displacing plasma water (indirect ISE) | Normal |
Pseudohyponatraemia is a measurement artefact with normal serum osmolality and needs no correction factor — direct ion-selective electrode or blood-gas sodium avoids it. The hyperglycaemic correction above is for a real osmotic shift.
Run it now: Corrected Sodium Calculator
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.