What is corrected sodium?

Corrected sodium is the estimated true serum sodium value adjusted for the dilutional effect of hyperglycemia. High blood glucose draws water out of cells, diluting the sodium concentration. Corrected sodium tells you what the sodium would be if glucose were at a normal level (~100 mg/dL).

Which formula should I use — Katz or Hillier?

Katz (N Engl J Med, 1973) worked out 1.6 mEq/L per 100 mg/dL from a theoretical model of water moving out of cells. Hillier and colleagues (Am J Med, 1999) raised glucose in 6 healthy volunteers and found an average fall of 2.4 mEq/L per 100 mg/dL. They also found the fall was not linear and was steeper above about 400 mg/dL. Many references report both values, which is why this calculator shows both.

What is the normal glucose baseline used?

The standard baseline is 100 mg/dL (5.6 mmol/L), representing the upper end of the normal fasting glucose range. Only glucose above this threshold is used in the correction calculation.

What if my glucose is below 100 mg/dL?

No correction is applied. The calculator only uses glucose above 100 mg/dL, so at 100 mg/dL or lower both formulas return the measured sodium and the correction shows +0.00 mEq/L.

Can I enter glucose in mmol/L?

Yes. Switch the unit next to the glucose box to mmol/L. The calculator converts at 18.018 mg/dL per mmol/L, so 20 mmol/L counts as 360 mg/dL, and the summary shows both values.

Is this tool a substitute for clinical judgment?

No. This calculator is an educational and clinical reference aid only. Always interpret results in the full clinical context and consult current clinical guidelines or a specialist when making treatment decisions.

Should I use measured or corrected sodium for the anion gap?

The anion gap (Na − Cl − HCO3) and calculated serum osmolality (2 × Na + glucose ÷ 18 + BUN ÷ 2.8) are normally worked out with the measured sodium. Glucose already enters the osmolality formula on its own. Corrected sodium estimates what the sodium will be once glucose comes back to normal.

What is the corrected sodium formula with glucose in mmol/L?

Divide the factors by 5.55, because 100 mg/dL of glucose is about 5.55 mmol/L. Katz becomes Na + 0.29 × (glucose − 5.55) and Hillier becomes Na + 0.43 × (glucose − 5.55). Or pick mmol/L next to the glucose box and the calculator converts for you.

Corrected Sodium Calculator

Enter measured sodium and glucose to get corrected serum sodium using the Katz and Hillier formulas.

Corrected sodium = measured sodium + 1.6 × (glucose − 100) ÷ 100, with glucose in mg/dL (Katz, 1973).

Patient Values

Measured Serum Sodium

mEq/L

Normal range: 135–145 mEq/L

Concurrent Serum Glucose

Must be above 100 mg/dL for correction to apply

Formulas Used

Katz (1.6): Corrected Na = Measured Na + 1.6 × [(Glucose − 100) / 100]

Hillier (2.4): Corrected Na = Measured Na + 2.4 × [(Glucose − 100) / 100]

Enter patient values and click Calculate

Quick answer

Corrected sodium = measured sodium + 1.6 × (glucose − 100) ÷ 100, with glucose in mg/dL (Katz, 1973). The Hillier formula (1999) uses 2.4 in place of 1.6. A sodium of 128 mEq/L with glucose at 600 mg/dL corrects to 136.0 by Katz or 140.0 by Hillier, and the calculator shows both.

Examples

Na / glucose	Katz 1.6	Hillier 2.4
135 / 100	135.0	135.0
130 / 300	133.2	134.8
124 / 400	128.8	131.2
128 / 600	136.0	140.0
125 / 800	136.2	141.8
134 / 1000	148.4	155.6

Enter measured sodium and glucose.

Summary

In hyperglycemia, high blood glucose causes osmotic fluid shifts from intracellular to extracellular space, diluting serum sodium. This dilutional drop is often called pseudohyponatremia, although that term strictly means a lab artifact from very high lipids or proteins. The corrected sodium calculator adjusts the measured sodium value to reflect what it would be at a normal glucose level. Two widely used formulas exist: the Katz formula (adds 1.6 mEq/L per 100 mg/dL glucose above normal) and the Hillier formula (adds 2.4 mEq/L per 100 mg/dL). Hillier's 1999 study found a larger drop than Katz predicted, especially above about 400 mg/dL.

How it works

Enter the measured (reported) serum sodium in mEq/L.
Enter the concurrent serum glucose in mg/dL, or switch the unit to mmol/L (converted at 18.018 mg/dL per mmol/L).
The calculator subtracts the normal glucose baseline (100 mg/dL) from the measured glucose.
The glucose excess is divided by 100 and multiplied by the correction factor (1.6 for Katz, 2.4 for Hillier).
The result is added to the measured sodium to produce the corrected sodium value.
Both formula results are displayed side by side for clinical comparison.

Use cases

Evaluate true sodium status in diabetic ketoacidosis (DKA).
Assess sodium in hyperglycemic hyperosmolar state (HHS).
Distinguish true hyponatremia from dilutional pseudohyponatremia.
Guide fluid and electrolyte management in critically ill patients.
Teaching medical students and residents about osmolar correction.
Quick bedside reference for emergency department providers.
Compare Katz vs. Hillier results when glucose exceeds 400 mg/dL.
Evaluate sodium before and after insulin therapy in DKA.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu