How do you calculate corrected sodium?
Add 1.6 or 2.4 mmol/L of sodium for every 100 mg/dL of glucose above 100 mg/dL. Very high glucose pulls water out of the cells and dilutes the sodium in the blood; the correction adds that dilution back.
Corrected Na (mmol/L) = measured Na + factor × (glucose mg/dL − 100) ÷ 100
- Factor 1.6 – Katz, 1973.
- Factor 2.4 – Hillier and colleagues, 1999.
- Glucose in mmol/L is converted first: mmol/L × 18 = mg/dL.
The calculator shows the result with the factor you chose and, underneath, the result with the other one. Both are given to up to one decimal place.
How to use the calculator
- Enter the Measured sodium in mmol/L (the same as mEq/L).
- Choose the Glucose unit (mmol/L or mg/dL) and enter the Glucose from the same sample.
- Choose the Correction factor: Katz (1.6) or Hillier (2.4).
- Read the Corrected sodium and compare it with the line for the other factor.
Worked examples
Example 1 – glucose in mmol/L. Sodium 130 mmol/L, glucose 33 mmol/L. 33 × 18 = 594 mg/dL. (594 − 100) ÷ 100 = 4.94. Katz: 130 + 1.6 × 4.94 = 137.9 mmol/L. Hillier: 130 + 2.4 × 4.94 = 141.9 mmol/L.
Example 2 – glucose in mg/dL. Sodium 131 mmol/L, glucose 450 mg/dL. (450 − 100) ÷ 100 = 3.5. Katz: 131 + 1.6 × 3.5 = 131 + 5.6 = 136.6 mmol/L. Hillier: 131 + 2.4 × 3.5 = 131 + 8.4 = 139.4 mmol/L.
Example 3 – severe hyperglycaemia. Sodium 126 mmol/L, glucose 800 mg/dL. (800 − 100) ÷ 100 = 7. Katz: 126 + 11.2 = 137.2 mmol/L. Hillier: 126 + 16.8 = 142.8 mmol/L. A very low measured sodium becomes normal or high once corrected.
How much is added
Amount added to the measured sodium at different glucose levels.
| Glucose | Katz (1.6) | Hillier (2.4) |
|---|---|---|
| 11.1 mmol/L (200 mg/dL) | +1.6 | +2.4 |
| 22.2 mmol/L (400 mg/dL) | +4.8 | +7.2 |
| 33.3 mmol/L (600 mg/dL) | +8.0 | +12.0 |
| 44.4 mmol/L (800 mg/dL) | +11.2 | +16.8 |
| 55.6 mmol/L (1000 mg/dL) | +14.4 | +21.6 |
The gap between the two factors grows with glucose. At 1000 mg/dL it reaches 7.2 mmol/L.
Common mistakes
- Wrong glucose unit. 25 mmol/L entered as mg/dL is read as a normal glucose, and the calculator says no correction is needed. 450 mg/dL left on mmol/L becomes 8,100 mg/dL and an impossible sodium above 250. It’s worth checking the unit on the report.
- Applying the factor per mmol/L. 1.6 and 2.4 refer to each 100 mg/dL of glucose (about 5.6 mmol/L), not to each 1 mmol/L. Let the calculator do the conversion.
- Calling it pseudohyponatraemia. The dilution is real; a lipid or protein artefact is a different problem.
- Treating the corrected value as a measured one. It is an estimate to help you read the trend, not a laboratory result.
Limits of the method
- The relationship is not perfectly linear. Hillier’s data suggest the fall in sodium per 100 mg/dL is greater at very high glucose, so neither factor is exact across the whole range.
- Other osmotic agents, such as mannitol, cause a similar dilution that the formula ignores.
- Fluids and insulin change sodium and glucose quickly. The correction describes one moment.
- Laboratory artefacts from severe hypertriglyceridaemia or paraproteins can lower the measured sodium regardless of glucose.
In hyperglycaemic emergencies, the serum osmolality calculator shows how concentrated the plasma really is, and the anion gap calculator helps spot ketoacidosis. To track what goes in and out during treatment, use the fluid balance calculator.
Frequently asked questions
What is the corrected sodium formula?
Corrected Na = measured Na + factor × (glucose in mg/dL − 100) ÷ 100. The factor is 1.6 (Katz) or 2.4 (Hillier). If you enter glucose in mmol/L, the calculator first multiplies it by 18 to convert it to mg/dL, then applies the formula.
Why does high glucose lower the sodium?
Because glucose draws water out of the cells. Without enough insulin, glucose stays in the blood and pulls water from inside the cells into the circulation. That extra water dilutes the sodium. The total amount of sodium has not changed, only its concentration.
Katz or Hillier: which factor should I use?
Both are in use, so it’s best to follow your local protocol. Katz (1.6 mmol/L per 100 mg/dL) came from a theoretical calculation in 1973. Hillier and colleagues (1999) measured the change in volunteers, found a larger effect and proposed 2.4. The calculator shows both results, so you can see the spread.
Is this pseudohyponatraemia?
Not strictly, even though the term is often used. True pseudohyponatraemia is a laboratory artefact caused by very high lipids or proteins. The low sodium of hyperglycaemia is real: it is a dilutional, sometimes called translocational, hyponatraemia. This correction does not address true pseudohyponatraemia.
What happens to the sodium as glucose falls?
It rises. As glucose comes down, water moves back into the cells and the measured sodium goes up. The corrected value gives an idea of where the measured sodium will settle, which helps when you review serial results during treatment of diabetic ketoacidosis or a hyperosmolar state.
Do I need the correction if glucose is normal?
No. At a glucose of 100 mg/dL (about 5.6 mmol/L) or below there is nothing to correct. The calculator then returns the measured sodium unchanged and shows the message “Glucose is not raised, so no correction is needed”. If you expected a high value, it’s worth checking the glucose unit.