What this calculator does
High blood glucose pulls water out of cells and into the bloodstream, which dilutes sodium. A measured sodium can therefore look low when total body sodium is normal, and correcting for glucose reveals what it would be without that dilution.
The two published formulas disagree, and the gap widens with glucose. At 400 mg/dL a measured 130 corrects to 134.8 by Katz and 137.2 by Hillier; at 700 mg/dL the two give 139.6 and 144.4.
The formula
Both formulas add a fixed amount of sodium for every 100 mg/dL that glucose exceeds 100. Katz uses 1.6 mEq/L per 100, and Hillier uses 2.4, based on a later experimental study.
| Term | Meaning |
|---|---|
| Corrected sodium | What sodium would read if glucose were normal. |
| Katz formula | The 1973 correction, adding 1.6 mEq/L per 100 mg/dL of excess glucose. |
| Hillier formula | The 1999 correction, adding 2.4 mEq/L, derived from direct measurement. |
The inputs explained
| Field | What to enter |
|---|---|
| Measured sodium (mEq/L) | Measured serum sodium in mEq/L. |
| Blood glucose (mg/dL) | Blood glucose in mg/dL. Both formulas measure the excess above 100. |
When to use it
Reading a panel during hyperglycaemia
A low sodium may reflect dilution rather than sodium depletion.
Understanding two different corrected values
Different sources use different formulas, which explains disagreeing figures.
Following sodium as glucose falls
Sodium normally rises as glucose is brought down, which the correction anticipates.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How far do the two formulas diverge?
The same measured sodium at three glucose levels.
| Blood glucose | Corrected sodium (Hillier) | Corrected sodium (Katz) |
|---|---|---|
| 200 mg/dL | 132.4 mEq/L | 131.6 mEq/L |
| 400 mg/dL | 137.2 mEq/L | 134.8 mEq/L |
| 700 mg/dL | 144.4 mEq/L | 139.6 mEq/L |
Questions
Which formula should be used?
Hillier's 2.4 factor came from a controlled experimental study and is often preferred, particularly at high glucose levels. Katz's 1.6 remains widely used and appears in many references. Practice varies, and the formula should be stated with any corrected value.
Why does high glucose lower sodium?
Because glucose is osmotically active and cannot freely enter cells without insulin. It draws water out of cells into the blood, diluting everything in the plasma including sodium, without changing the total amount of sodium present.
Is the corrected value what should be treated?
That is a clinical judgement, not an arithmetic one. The correction indicates whether a sodium abnormality is real or dilutional, but management of both glucose and sodium in that situation requires specialist care.
Does the correction apply at normal glucose?
It has no effect. Both formulas measure the excess above 100 mg/dL, so at or below that level the corrected value equals the measured one.
For overall dissolved particle concentration, see the serum osmolality calculator. For the unmeasured ion balance, see the anion gap calculator.