Free Sodium Correction Calculator

The free Sodium Correction Calculator is a practical medical sodium calculator designed to refine serum sodium (Na⁺) measurements in the presence of hyperglycemia. By incorporating the standard corrected sodium formula—particularly the Hillier formula—this tool delivers a corrected sodium value that reflects the patient’s true sodium balance. Clinicians dealing with electrolyte disturbances can rely on this serum sodium correction tool to adjust for the diluting effect of high blood glucose.

Mechanism: Why Hyperglycemia Lowers Measured Sodium

When blood glucose rises well above normal, the osmotic gradient draws water from the intracellular space into the extracellular compartment. This fluid shift increases the plasma volume and dilutes sodium, leading to a measured serum Na⁺ that is lower than the actual total body sodium. The hyperglycemia sodium correction formula accounts for this artifact, providing a more accurate assessment.

Corrected Sodium Formulas: Hillier and Katz

Two equations have been proposed for correcting sodium in hyperglycemia. The current standard is the Hillier formula (published in 1998), expressed as:

$$\text{Corrected Na⁺} = \text{Measured Na⁺} + 0.024 \times (\text{Glucose} - 100)$$

An older version, the Katz formula (1973), uses a smaller factor:

$$\text{Corrected Na⁺} = \text{Measured Na⁺} + 0.016 \times (\text{Glucose} - 100)$$

Both expect glucose in mg/dL. The Hillier version is generally preferred because it more accurately reflects the dilution effect. The calculator includes both equations, allowing you to compare the results.

How to Use the Free Sodium Correction Calculator

Using this tool is straightforward:

• Enter the patient’s serum sodium level (mmol/L and mEq/L are numerically the same).
• Input the blood glucose concentration. You can choose between mg/dL and mmol/L; the calculator automatically converts if needed.
• The corrected sodium appears instantly, calculated with the Hillier formula by default.
• To see the result from the Katz formula, open the additional settings section.

This setup makes it easy to obtain both estimates without manual calculation.

Worked Examples

Hyperglycemia case
Measured Na⁺: 135 mEq/L, glucose: 210 mg/dL
Using the Hillier formula:

$$135 + 0.024 \times (210 - 100) = 135 + 2.64 = 137.64\ \text{mEq/L}$$

The corrected value is slightly higher than the measured one, confirming that the true sodium is underestimated.

Hypoglycemia case
Measured Na⁺: 142 mEq/L, glucose: 70 mg/dL

$$142 + 0.024 \times (70 - 100) = 142 - 0.72 = 141.28\ \text{mEq/L}$$

Here the measured sodium overestimates the true level, and correction brings the value down.

Interpreting the Corrected Sodium

The corrected sodium should be used when evaluating hyponatremia or hypernatremia in patients with abnormal glucose. The formula works bidirectionally—it corrects underestimation caused by hyperglycemia and overestimation caused by hypoglycemia. In practice, this means that any significant glucose abnormality prompts a recalculation of the sodium level.

Diabetes, through its fluctuations in blood sugar, can chronically influence electrolyte readings. High glucose tends to mask true hyponatremia, while low glucose can exaggerate it. By integrating the Hillier formula into a free, easy‑to‑use interface, the Sodium Correction Calculator assists clinicians in avoiding misinterpretation of lab results. This serum sodium correction tool is especially valuable in acute care settings where rapid decisions about fluid therapy are needed.