A low serum sodium in a patient with high blood glucose is often not a true hyponatremia — it's a downstream effect of the hyperglycemia. Treating the wrong number can do real harm.
This guide walks through the Hillier formula (2018), the legacy Katz formula, the concept of pseudohyponatremia, and the clinical interpretation in diabetic ketoacidosis (DKA).
The formula
The modern Hillier formula corrects sodium by 2.4 mEq/L for each 100 mg/dL of glucose above 100 mg/dL:
Corrected Na = Measured Na + 2.4 × ((Glucose − 100) / 100)
Katz's 1973 formula uses a factor of 1.6 and underestimates the correction. Hillier's 1999/2018 hypertonic glucose-infusion experiments showed 2.4 fits real-world data better.
Clinical context: DKA & pseudohyponatremia
Consider a patient in DKA: glucose 600 mg/dL, sodium 130 mEq/L. At first glance — hyponatremia. With Hillier:
130 + 2.4 × ((600 − 100) / 100) = 130 + 12 = 142 mEq/L
Corrected sodium is normal — this is pseudohyponatremia from the hyperglycemia, not a true sodium deficit. Treatment targets glucose, not sodium.
Reference ranges
| Corrected sodium | Classification |
|---|---|
| < 135 mEq/L | Hyponatremia |
| 135 – 145 mEq/L | Normal |
| > 145 mEq/L | Hypernatremia |
Step-by-step
- 1.Gather the lab values: serum sodium (mEq/L) and glucose (mg/dL or mmol/L).
- 2.Compute the difference: subtract 100 from glucose, divide by 100.
- 3.Add the correction: multiply by 2.4 (Hillier) and add to measured sodium.
Related calculators
- Blood sugar converter — convert glucose between mg/dL and mmol/L. Open the blood sugar converter.
- Diabetes risk score — FINDRISC for type-2 diabetes. Open the diabetes risk calculator.
- HbA1c converter — long-term glycemia between %, mmol/mol, and average glucose. Open the HbA1c converter.
Calculate corrected sodium now
Enter sodium and glucose — get a corrected value and clinical classification instantly.
Open the Sodium Correction Calculator →Frequently asked questions
When should I correct sodium for hyperglycemia?
Whenever serum glucose exceeds 200 mg/dL and sodium is abnormal. High glucose draws water into the extracellular space and lowers sodium by roughly 2.4 mEq/L per 100 mg/dL of glucose above 100 mg/dL.
Hillier or Katz — which formula is standard?
The Hillier formula (factor 2.4) from 2018 is today's standard. The older Katz formula (factor 1.6) from 1973 underestimates the correction and is now rarely used.
What is pseudohyponatremia?
Apparent hyponatremia caused by hyperglycemia, hyperlipidemia, or hyperproteinemia. Once corrected, sodium is normal — there is no true deficit. Classic in diabetic ketoacidosis (DKA).
How do I convert glucose from mmol/L to mg/dL?
Multiply mmol/L by 18.0182. Example: 22.2 mmol/L × 18 ≈ 400 mg/dL.