🧪 Corrected Sodium in Hyperglycemia: Why, When, and How

A practical guide to how hyperglycemia distorts the measured sodium, and when to use the Katz and Hillier equations to estimate true sodium and avoid diagnostic errors.

When blood glucose is markedly elevated, a patient's labs may show a falsely low sodium. Understanding and correcting this phenomenon is essential to avoid misdiagnosis and inappropriate management, especially in diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS).

Why does high glucose lower sodium?

Glucose is an osmotically active solute confined to the extracellular space. When it rises, it draws water from inside the cells into the blood, diluting the measured sodium concentration.

> The result: sodium appears low even though total body sodium may be normal. This is called translocational (dilutional) hyponatremia, not true hyponatremia.

The values and the two accepted equations

Corrected sodium adds a fixed amount for every 100 mg/dL of glucose above 100:

| Equation | Correction factor | Notes |

|---|---|---|

| Katz (1973) | 1.6 mEq/L | The classic formula |

| Hillier (1999) | 2.4 mEq/L | More accurate, especially when glucose >400 |

General formula:

Corrected Na = Measured Na + factor × [(Glucose − 100) ÷ 100]

Worked example

• Measured sodium: 130 mEq/L
• Glucose: 600 mg/dL
• Using Hillier: 130 + 2.4 × [(600 − 100) ÷ 100] = 142 mEq/L

Interpretation: true sodium is normal — the apparent drop was caused by glucose alone.

Why does it matter clinically?

• Prevents misdiagnosing a true hyponatremia that does not exist.
• Guides fluid management in DKA and HHS more accurately.
• Unmasks true hyponatremia: if the corrected sodium remains low, a genuine sodium deficit exists and needs separate evaluation.

Points of caution

• The equation is an estimate, not a direct lab value.
• Use Hillier for severe hyperglycemia (>400 mg/dL).
• Correct glucose gradually; rapid correction can affect osmotic balance.

Try it now: Use the [Corrected Sodium & Osmolality Analyzer](https://www.medclac.com/#open=corrected_sodium) to get the result from both equations plus an estimated serum osmolality.

Disclaimer: This content is for educational guidance only and does not replace professional medical consultation.