Corrected Sodium
Adjust a measured sodium for a raised blood glucose, using the Katz and Hillier factors.
Adds 1.6 mEq/L for every 100 mg/dL of glucose above 100 — here 5 × 1.6 = 8 mEq/L.
The Hillier factor of 2.4 fits better at glucose levels above about 400 mg/dL.
Add 1.6 mEq/L to the measured sodium for every 100 mg/dL of glucose above 100. With a sodium of 130 mEq/L and glucose of 600 mg/dL that is 130 + 1.6 × 5 = 138 mEq/L. The Hillier factor of 2.4 gives 142 mEq/L instead.
Why hyperglycaemia lowers the measured sodium
Glucose that cannot enter cells stays in the extracellular fluid, where it is osmotically active. Water follows it out of the cells and into the plasma, diluting everything already dissolved there — including sodium. The result is a real but dilutional hyponatraemia: the sodium concentration has fallen, while the total body sodium has not necessarily changed at all.
Correcting for glucose answers a specific question: what would this patient’s sodium be if the glucose were normal? That matters because the answer changes the interpretation. A measured sodium of 130 with a glucose of 600 mg/dL is not a sodium-losing state; corrected, the sodium is around 138 and the picture is one of hyperglycaemia rather than hyponatraemia.
Katz or Hillier
The classic factor, published by Katz in 1973, adds 1.6 mEq/L per 100 mg/dL of glucose above normal. Later experimental work by Hillier and colleagues found the relationship is not linear and suggested 2.4 fits better, particularly at glucose levels above roughly 400 mg/dL. Both remain in use, and this calculator shows the two side by side.
Glucose in mmol/L is multiplied by 18.016 to convert to mg/dL. No correction is needed when glucose is at or below 100 mg/dL.
Worked example: sodium 130 mEq/L, glucose 600 mg/dL
Work out how far the glucose is above normal in hundreds, then scale it:
- 1 Convert the glucose to mg/dL if needed. A result in mmol/L is multiplied by 18.016 — 33.3 mmol/L is about 600 mg/dL.
- 2 Subtract the normal glucose. 600 − 100 = 500 mg/dL above normal.
- 3 Express that in hundreds. 500 ÷ 100 = 5.
- 4 Apply the Katz factor. 130 + 1.6 × 5 = 130 + 8 = 138 mEq/L.
- 5 Compare with Hillier. 130 + 2.4 × 5 = 130 + 12 = 142 mEq/L. At this glucose level the two differ by 4 mEq/L.
Correction added at common glucose levels
Amount added to the measured sodium, in mEq/L, by each factor.
| Glucose (mg/dL) | Glucose (mmol/L) | Katz (1.6) | Hillier (2.4) |
|---|---|---|---|
| 200 | 11.1 | +1.6 | +2.4 |
| 300 | 16.7 | +3.2 | +4.8 |
| 400 | 22.2 | +4.8 | +7.2 |
| 600 | 33.3 | +8.0 | +12.0 |
| 800 | 44.4 | +11.2 | +16.8 |
| 1000 | 55.5 | +14.4 | +21.6 |
Reading the corrected value
The corrected sodium is a way of seeing past the dilution, not a value to be treated in its own right. Its usual role is to reveal what is happening underneath: a corrected sodium that is normal or high in diabetic ketoacidosis or a hyperosmolar state points to a substantial free-water deficit, even though the measured sodium looked low.
As glucose falls with treatment, water moves back into the cells and the measured sodium rises on its own — an expected change rather than a new problem. Watching that rise, and its rate, is part of monitoring the correction. Sodium correction that proceeds too quickly carries its own risks, which is why these decisions belong to a treating team working from serial measurements.
This tool is an informational calculation for study and practice, not medical advice. Fluid and electrolyte management must be directed by a qualified professional.