Sodium Correction Calculator
High blood sugar makes a blood test show a falsely low sodium level. This free calculator corrects the measured sodium for hyperglycemia using the Katz and Hillier formulas, so you can see what the sodium would be if glucose were normal. Glucose can be entered in mg/dL or mmol/L.
Why does high glucose lower sodium?
Glucose stays mainly in the blood and does not enter cells easily without insulin. When blood glucose is very high, it pulls water out of the cells into the bloodstream. This extra water dilutes the sodium in the blood, so the measured sodium falls even though the total amount of sodium in the body has not changed. This is called translocational or hyperglycemic hyponatremia.
Correcting the sodium estimates what the level would be once the glucose returns to normal and the water moves back into the cells. It helps doctors see whether a patient also has a true sodium problem, which is common in diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS).
Corrected sodium formulas
Both formulas add sodium for every 100 mg/dL of glucose above 100 mg/dL (5.6 mmol/L):
| Formula | Equation |
|---|---|
| Katz (1973) | Measured Na + 1.6 × (glucose − 100) ÷ 100 |
| Hillier (1999) | Measured Na + 2.4 × (glucose − 100) ÷ 100 |
Glucose is in mg/dL. To convert mmol/L to mg/dL, multiply by 18.
Example: measured sodium 130 mEq/L and glucose 600 mg/dL. The glucose is 500 above 100, which is 5 lots of 100.
| Formula | Working | Corrected sodium |
|---|---|---|
| Katz | 130 + 1.6 × 5 | 138 mEq/L |
| Hillier | 130 + 2.4 × 5 | 142 mEq/L |
In this example the sodium looks low, but once corrected it is normal, meaning the low reading was caused by the high glucose.
Katz or Hillier: which formula is better?
The Katz factor of 1.6 was worked out from theory. The Hillier study measured sodium directly in volunteers whose glucose was raised, and found an average drop of about 2.4 mEq/L per 100 mg/dL, with an even larger effect above 400 mg/dL. Many references now favour Hillier, especially at high glucose, while Katz is still widely taught. Showing both gives a sensible range.
Effective osmolality
Effective (or tonicity) osmolality is estimated as 2 × sodium + glucose ÷ 18. The normal range is about 275–295 mOsm/kg. Values above 320 mOsm/kg are one of the features of HHS. It leaves out urea, which crosses cell membranes freely and does not move water between cells and blood.
Normal sodium levels
| Level (mEq/L) | Meaning |
|---|---|
| Below 135 | Hyponatremia (low sodium) |
| 135 – 145 | Normal |
| Above 145 | Hypernatremia (high sodium) |
If the corrected sodium is still low, there may be another cause of low sodium. If it is high, the person may be significantly dehydrated. Both need medical assessment.
Limitations
The formulas give an estimate. The real effect varies between people and depends on kidney function, hydration and how quickly glucose changes. Sodium and glucose should be rechecked regularly during treatment. A falsely low sodium can also be caused by very high blood fats or proteins (pseudohyponatremia), which these formulas do not correct.
Frequently asked questions
What is corrected sodium?
It is the sodium level adjusted for high blood glucose. It estimates what the sodium would be if the glucose were normal.
How do you calculate corrected sodium?
Add 1.6 (Katz) or 2.4 (Hillier) mEq/L to the measured sodium for every 100 mg/dL of glucose above 100 mg/dL.
When should sodium be corrected for glucose?
When blood glucose is clearly raised, for example in DKA or HHS. At normal glucose levels no correction is needed.
Is corrected sodium used for treatment decisions?
Doctors use it alongside other tests and the patient's condition. It should never be used on its own to decide fluid or sodium treatment.
How do I convert glucose from mmol/L to mg/dL?
Multiply by 18. For example, 20 mmol/L is about 360 mg/dL.