Sodium Correction Calculator
High blood glucose pulls water into the bloodstream and dilutes sodium, so a measured value can look falsely low. This calculator estimates the corrected (true) sodium using the Katz (1.6) or Hillier (2.4) factor, compares both, and adds effective serum osmolality so you can read the result in context.
Formula
Worked example
A patient has a measured sodium of 130 mEq/L and glucose of 400 mg/dL. With the Katz factor the correction is 1.6 × (400 − 100)/100 = 4.8 mEq/L, giving a corrected sodium of about 134.8 mEq/L, still mildly low, so true hyponatremia is present. The Hillier factor of 2.4 would give 137.2 mEq/L. Effective osmolality is 2 × 130 + 400/18 ≈ 282 mOsm/kg.
Why high glucose lowers measured sodium
Glucose is an osmotically active solute. When blood sugar rises sharply, water shifts out of cells and into the bloodstream to balance the higher osmolality, and that extra water dilutes the sodium that is already there. The lab therefore reports a sodium concentration that looks lower than the body's true sodium status, a phenomenon called pseudohyponatremia or dilutional hyponatremia. Correcting for glucose lets you judge whether the patient is genuinely sodium-depleted or simply diluted by hyperglycemia.
Katz 1.6 versus Hillier 2.4
The widely taught Katz rule adds 1.6 mEq/L of sodium for every 100 mg/dL that glucose sits above the normal 100 mg/dL baseline, so at a glucose of 600 mg/dL the measured sodium is adjusted upward by 1.6 × 5 = 8 mEq/L. The Hillier factor of 2.4 mEq/L per 100 mg/dL, derived from a 1999 experimental study, fits better when glucose climbs above roughly 400 mg/dL. Pick whichever your institution prefers in the dropdown; the calculator always shows the result from the other factor alongside it so you can see how much the choice changes the estimate. In most cases both land in the same clinical band.
Glucose units and effective osmolality
Many labs outside the United States report glucose in mmol/L. Switch the glucose unit and the calculator converts to mg/dL first (mmol/L times 18.02) before applying the correction, so you never have to convert by hand. The optional effective serum osmolality output estimates tonicity as 2 times the measured sodium plus glucose divided by 18. It deliberately leaves out urea, since urea crosses cell membranes freely and does not drive water shifts. An effective osmolality above about 320 mOsm/kg signals a hyperosmolar state such as hyperosmolar hyperglycemic state (HHS).
Interpreting and acting on the result
A corrected sodium that is still low points to true hyponatremia that may need its own evaluation, while a corrected value in the normal range suggests the low reading was mostly dilutional and will rise as glucose is treated. Either way the priority in conditions like diabetic ketoacidosis or hyperosmolar hyperglycemic state is careful fluid and insulin management with frequent re-checks. These results are estimates only; diagnosis, fluid choices, and correction rates are clinical decisions that must be made by a qualified healthcare professional who can assess the whole patient.
Serum sodium reference ranges
| Sodium (mEq/L) | Category |
|---|---|
| < 135 | Hyponatremia (low) |
| 135-145 | Normal |
| > 145 | Hypernatremia (high) |
Apply these bands to the corrected sodium, not the raw measured value, when significant hyperglycemia is present.
Frequently asked questions
Should I use the 1.6 or 2.4 correction factor?
The traditional Katz 1.6 mEq/L per 100 mg/dL factor is the most widely cited default. Research by Hillier and colleagues suggests 2.4 mEq/L is more accurate at very high glucose levels (above about 400 mg/dL). This calculator lets you pick either and always shows the other for comparison; in practice the two give similar clinical impressions, so follow your institution's preferred convention.
My lab reports glucose in mmol/L. Can I still use this?
Yes. Switch the glucose unit to mmol/L and enter your value directly. The calculator multiplies by 18.02 to convert to mg/dL before applying the correction, so the corrected sodium and osmolality come out the same as if you had converted by hand.
What is effective serum osmolality and why include it?
Effective osmolality (tonicity) is the part of serum osmolality that actually drives water across cell membranes. It is estimated as 2 times sodium plus glucose divided by 18, deliberately excluding urea. It is especially useful in diabetic ketoacidosis and hyperosmolar hyperglycemic state, where a value above roughly 320 mOsm/kg flags a hyperosmolar emergency. Normal is about 275 to 295 mOsm/kg.
Is corrected sodium the same as the value the lab should report?
No. The lab reports the actual measured sodium concentration, which is correct. The corrected sodium is a calculated estimate of what the sodium would be if glucose were normal, used to decide whether a low reading reflects true depletion or just dilution by high glucose.
Does this replace clinical judgment?
No. This is an educational estimate of corrected sodium and osmolality. Managing hyperglycemia, hyponatremia, or hypernatremia involves osmolality, volume status, symptoms, and safe correction rates that only a clinician can weigh. Always confirm with a doctor before acting on a result.