Corrected Sodium Calculator

Q: Do you use corrected or measured sodium for the anion gap?

Use the measured sodium for the anion gap. The anion gap compares the actual charged particles in that blood sample, so the raw lab value is the right one. Same rule for serum osmolality: use measured sodium, because the real, diluted sodium is what the blood osmolality depends on. Corrected sodium is mainly for judging the body's true water and salt balance and for picking IV fluids.

Q: What is the difference between true hyponatremia and pseudohyponatremia?

True hyponatremia means the body really has too little salt for its water, often from vomiting, diuretics, or SIADH. Pseudohyponatremia means the lab number is low but the body's salt balance is fine. High sugar pulls water into the blood and dilutes the sodium. Correcting for glucose tells you which one you are dealing with. If the corrected number lands back in the 136 to 145 range, the low reading was mostly a sugar effect.

Introduction

The Corrected Sodium Calculator estimates a patient's true serum sodium when blood sugar is high. High glucose pulls water out of cells and into the blood. That extra water thins the blood and makes the sodium reading on the lab report look lower than it really is. This is called dilutional or false hyponatremia.

To find the real number, you add sodium back based on how far glucose is above 100 mg/dL. This tool uses both common formulas:

Katz formula: add 1.6 mEq/L for every 100 mg/dL of glucose over 100.
Hillier formula: add 2.4 mEq/L for every 100 mg/dL of glucose over 100. Many clinicians prefer this one when glucose is above 400 mg/dL.

Enter the measured sodium and the serum glucose. You can use mEq/L or mmol/L for sodium, and mg/dL or mmol/L for glucose. The calculator returns both corrected values, compares them to the normal range of 136 to 145 mEq/L, and shows the full math step by step.

This matters most in diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS). Knowing the corrected sodium helps guide fluid choices and lowers the risk of moving sodium too fast, which can harm the brain.

How to use our Corrected Sodium Calculator

Enter the patient's measured serum sodium and serum glucose. The calculator shows the corrected sodium using both the Katz formula (1.6) and the Hillier formula (2.4), tells you if each result is low, normal, or high, and shows the math step by step.

Measured Sodium: Type the sodium value from the lab report. Then pick your unit, mEq/L or mmol/L. For sodium, both units give the same number, so only the label changes. A normal result is 136 to 145.

Serum Glucose: Type the blood sugar value from the same lab draw. Then pick mg/dL or mmol/L. If you pick mmol/L, the tool changes it to mg/dL for you before it does the math. A normal fasting result is 70 to 100 mg/dL.

Calculate and Clear/Reset: Results update as you type, so you can press Calculate to refresh them or press Clear/Reset to empty both fields and start a new patient.

What Is Corrected Sodium?

Corrected sodium is the sodium level a person would have if their blood sugar were normal. High blood sugar pulls water out of cells and into the blood. That extra water thins the blood and makes the sodium number on the lab report look lower than it really is. This is called dilutional hyponatremia or pseudohyponatremia from hyperglycemia.

Why Glucose Changes the Sodium Reading

Glucose cannot enter most cells without insulin. When sugar builds up in the blood, it acts like a sponge and draws water out of cells. More water in the blood means each liter holds less sodium. So the sodium drops, even though the body has not truly lost salt. Once the sugar comes down with treatment, the sodium usually rises back on its own.

The Two Formulas

Both formulas add sodium back for every 100 mg/dL of glucose above 100 mg/dL:

Katz (1.6): Corrected Na⁺ = Measured Na⁺ + 1.6 × [(Glucose − 100) ÷ 100]. This is the older, classic factor.
Hillier (2.4): Corrected Na⁺ = Measured Na⁺ + 2.4 × [(Glucose − 100) ÷ 100]. This newer factor matches what happens in real patients more closely, especially when glucose is above 400 mg/dL.

Normal Sodium Range

Normal serum sodium is about 136 to 145 mEq/L. Below 136 is hyponatremia (low sodium). Above 145 is hypernatremia (high sodium). For sodium, mEq/L and mmol/L are the same number.

Why It Matters

Sodium controls how much water sits inside and outside brain cells. If sodium is fixed too fast, or if the real sodium level is misread, the brain can swell or shrink. Very fast correction of true low sodium can cause a serious brain injury called osmotic demyelination syndrome. Knowing the corrected value helps doctors decide if the low reading is real salt loss or just a sugar effect, and it guides safe fluid and insulin treatment.

When It Is Used

Corrected sodium is most useful in diabetic ketoacidosis (DKA), hyperosmolar hyperglycemic state (HHS), and any patient with very high blood sugar. Signs of low sodium include headache, nausea, confusion, weakness, muscle cramps, and in bad cases seizures or coma.

Limits to Keep in Mind

These formulas give an estimate, not an exact answer. They do not account for kidney disease, high fats or proteins in the blood, water loss from urinating a lot, or medicines that affect sodium. Always read the result next to the full clinical picture, and have a doctor make the treatment plan.

Formulas used

Glucose unit conversion (mmol/L to mg/dL)

\text{Glucose}_{\text{mg/dL}} = \text{Glucose}_{\text{mmol/L}} \times 18.0182

Glucose above the 100 mg/dL baseline

\Delta_{\text{glucose}} = \text{Glucose}_{\text{mg/dL}} - 100

Corrected sodium — Katz formula (factor 1.6)

\text{Na}^{+}_{\text{corr,Katz}} = \text{Na}^{+}_{\text{measured}} + 1.6 \times \frac{\text{Glucose}_{\text{mg/dL}} - 100}{100}

Corrected sodium — Hillier formula (factor 2.4)

\text{Na}^{+}_{\text{corr,Hillier}} = \text{Na}^{+}_{\text{measured}} + 2.4 \times \frac{\text{Glucose}_{\text{mg/dL}} - 100}{100}

Shift versus measured sodium

\Delta_{\text{Na}} = \text{Na}^{+}_{\text{corr}} - \text{Na}^{+}_{\text{measured}}

Interpretation versus reference range

\text{Na}^{+} < 136 \Rightarrow \text{Low} \quad 136 \le \text{Na}^{+} \le 145 \Rightarrow \text{Normal} \quad \text{Na}^{+} > 145 \Rightarrow \text{High}

Frequently asked questions

Which sodium correction factor is more accurate, 1.6 or 2.4?

The 2.4 factor (Hillier) fits real patients better, especially when glucose is above 400 mg/dL. It came from a study where healthy people were given glucose and their sodium was tracked.

The 1.6 factor (Katz) came from an older math model. It works well enough at mildly high sugars but tends to under-correct at very high sugars.

Many hospitals still report the 1.6 value out of habit, so it helps to look at both numbers.

At what blood sugar level should sodium be corrected?

Both formulas start counting once glucose passes 100 mg/dL (5.6 mmol/L). Below that, there is nothing to add.

In practice, the change only matters clinically when glucose is well above 200 mg/dL. At 200 mg/dL the shift is only about 1.6 to 2.4 mEq/L. At 600 mg/dL it jumps to 8 to 12 mEq/L, which can turn a scary low reading into a normal one.

What happens to sodium when blood sugar comes down with insulin?

Sodium usually rises. As glucose leaves the blood, water moves back into cells, so the blood gets less watered down and the sodium number climbs.

That is why doctors watch sodium every few hours during DKA treatment. If sodium does not rise as sugar falls, the patient may be getting too much free water, which raises the risk of brain swelling.

Do you use corrected or measured sodium for the anion gap?

Use the measured sodium for the anion gap. The anion gap compares the actual charged particles in that blood sample, so the raw lab value is the right one.

Same rule for serum osmolality: use measured sodium, because the real, diluted sodium is what the blood osmolality depends on.

Corrected sodium is mainly for judging the body's true water and salt balance and for picking IV fluids.

What is the difference between true hyponatremia and pseudohyponatremia?

True hyponatremia means the body really has too little salt for its water, often from vomiting, diuretics, or SIADH.

Pseudohyponatremia means the lab number is low but the body's salt balance is fine. High sugar pulls water into the blood and dilutes the sodium.

Correcting for glucose tells you which one you are dealing with. If the corrected number lands back in the 136 to 145 range, the low reading was mostly a sugar effect.

How fast can low sodium be raised safely?

For long-standing (chronic) low sodium, the usual limit is about 8 to 10 mEq/L in 24 hours, with some guidelines capping it at 6 to 8 mEq/L in high-risk patients.

Going faster can cause osmotic demyelination syndrome, where the coating on brain nerve cells is damaged. It can lead to trouble speaking, swallowing, or moving, and it may not get better.

In DKA, sodium often rises on its own as sugar falls, so that rise counts toward the daily limit.

What does it mean if measured sodium is low but corrected sodium is high?

It means the patient is actually dried out and short of water, not short of salt. The high sugar was hiding a true hypernatremia.

This is common in hyperosmolar hyperglycemic state (HHS), where people urinate out huge amounts of water. These patients need careful fluid replacement, and the sodium must be brought down slowly.

Does corrected sodium change which IV fluid is used in DKA?

Yes. It helps guide the choice after the first fluid bolus.

Corrected sodium normal or high: many protocols switch to half-normal saline (0.45%).
Corrected sodium low: stay with normal saline (0.9%) or a balanced fluid.

The goal is to replace water without dropping the blood's particle load too fast, which protects the brain.

What sodium level is considered dangerous?

Below 125 mEq/L is usually called severe hyponatremia and can cause confusion, seizures, and coma. Below 120 is a medical emergency.

On the high side, above 155 to 160 mEq/L is severe hypernatremia and can cause weakness, agitation, and coma.

How fast the level changed matters as much as the number. A quick drop causes symptoms at higher levels than a slow one.

Can high fat or protein in the blood cause a false low sodium too?

Yes. Very high triglycerides or very high proteins (like in multiple myeloma) take up space in the blood sample. Older lab machines then report a falsely low sodium.

This is a lab artifact, not a water shift, so the glucose formulas do not fix it. The lab can run the sample with a direct ion-selective electrode to get the true value.

How do you convert glucose from mmol/L to mg/dL?

Multiply mmol/L by 18 to get mg/dL. To go the other way, divide mg/dL by 18.

Examples: 5.5 mmol/L is about 100 mg/dL, 22 mmol/L is about 400 mg/dL, and 33 mmol/L is about 600 mg/dL.

Sodium is different. For sodium, mEq/L and mmol/L are the same number, so no math is needed.

Does sodium correction work the same way in children?

The formulas are the same, and corrected sodium is used in pediatric DKA too. The correction factor does not change with age or size.

But children have a higher risk of brain swelling during DKA treatment, so fluid rates and sodium changes are watched even more closely. Treatment should follow a pediatric DKA protocol.

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