Corrected Sodium Calculator

Background.

A corrected sodium calculator estimates what a measured serum sodium might look like after accounting for hyperglycemia. The common clinical situation is a patient whose serum sodium appears low while the serum glucose is high. Glucose is an effective extracellular osmole when it is acutely elevated, so water shifts from the intracellular compartment into the extracellular compartment. That water shift can dilute extracellular sodium concentration. The calculator does not say that the measured sodium is fake; it estimates the sodium concentration after removing the glucose-related water shift from the arithmetic.

The example in this dossier uses measured sodium of 128 mEq/L and glucose of 540 mg/dL. Glucose is 440 mg/dL above the default reference of 100 mg/dL. Expressed in 100 mg/dL increments, that excess is 4.4. With the classic Katz factor, the sodium add-back is 1.6 times 4.4, or 7.04 mEq/L. The Katz corrected sodium is therefore 135.04 mEq/L. With the Hillier factor, the add-back is 2.4 times 4.4, or 10.56 mEq/L. The Hillier corrected sodium is 138.56 mEq/L. The same measured laboratory values therefore produce a clinically visible difference depending on which correction factor the product shows.

That formula choice is the core product requirement. Many bedside references and older treatment algorithms use the Katz 1.6 mEq/L per 100 mg/dL correction. Hillier and colleagues found a larger overall correction factor in experimental data and noted that the traditional 1.6 factor can underestimate the relationship, especially at higher glucose concentrations. A calculator that returns only one number without labeling the factor can mislead users. Quanta should support Katz, Hillier, and both-formula display. The default can show both, with a clear label for each.

The calculator can also report glucose in mmol/L and an effective osmolality estimate. For glucose entered in mg/dL, glucose in mmol/L is glucose divided by 18. In the example, 540 divided by 18 equals 30 mmol/L. A common effective osmolality estimate excludes urea and uses two times measured sodium plus glucose divided by 18. With measured sodium of 128 and glucose of 540, the estimate is 2 times 128 plus 30, or 286 mOsm/kg. This value is not the same thing as measured osmolality, and it should be labeled as an estimate.

Corrected sodium is useful in DKA, HHS, severe hyperglycemia, and electrolyte review because it helps separate glucose-related translocational sodium change from additional water or sodium disorders. If corrected sodium remains low, there may be true hyponatremia in addition to hyperglycemia. If corrected sodium is high, the patient may have substantial water deficit. Those interpretations are clinical and depend on volume status, kidney function, measured osmolality, acid-base status, insulin treatment, fluid therapy, symptoms, and rate of change.

For Quanta, the calculator should keep the arithmetic transparent. It should show the glucose increment, the factor used, the corrected values, and the limitation that this is not a diagnostic or treatment protocol. It should reject negative sodium or glucose values, handle glucose values at or below the target by returning the measured sodium unchanged, and avoid presenting a single corrected sodium as a universal truth. Clinical teams should interpret results with the full laboratory panel and patient context.

What is corrected sodium calculator?

Corrected sodium is a calculated sodium value used when serum glucose is elevated. Hyperglycemia changes extracellular tonicity and can lower the measured serum sodium concentration by drawing water out of cells. The corrected sodium estimate adds back a factor for each 100 mg/dL of glucose above a selected reference, commonly 100 mg/dL.

The key terms are measured sodium, corrected sodium, hyperglycemia, Katz factor, Hillier factor, glucose increment, effective osmolality, DKA, HHS, hyponatremia, water deficit, and target glucose. Measured sodium is the laboratory sodium concentration at the time of blood draw. Corrected sodium is a formula estimate. The Katz factor adds 1.6 mEq/L for each 100 mg/dL glucose above 100 mg/dL. The Hillier factor adds 2.4 mEq/L for the same glucose increment. Effective osmolality is often estimated as two times sodium plus glucose divided by 18 when glucose is in mg/dL.

The calculator is valid for arithmetic from a measured sodium and glucose. It is not valid for diagnosing the cause of hyponatremia, deciding fluid tonicity, managing DKA or HHS alone, replacing measured osmolality, assessing chronic sodium correction safety, or overriding clinical judgment. It should be used as a transparent formula tool and interpreted with the patient, laboratory method, acid-base findings, kidney function, and treatment plan.

How to use this calculator.

1. 01Enter the measured serum sodium from the basic metabolic panel.
2. 02Enter the serum glucose and confirm the glucose unit.
3. 03Leave the target glucose at 100 mg/dL unless a protocol specifies a different reference.
4. 04Choose Katz, Hillier, or both correction factors.
5. 05Review the corrected sodium values and the glucose increment above target.
6. 06If enabled, review effective osmolality as a separate estimate.
7. 07Interpret the results with the full clinical picture, not as a stand-alone treatment decision.

The formula.

The calculator starts by converting glucose to mg/dL if needed. If the user enters glucose in mmol/L, the product multiplies by 18. If the user enters glucose in mg/dL, the calculator uses that value directly and can still display glucose in mmol/L by dividing by 18. The worked example has glucose of 540 mg/dL, so glucose in mmol/L is 540 divided by 18, which equals 30.

Next, the calculator finds how far glucose is above the target reference. The default target is 100 mg/dL. The excess glucose is 540 minus 100, or 440 mg/dL. Because both Katz and Hillier factors are expressed per 100 mg/dL, the calculator divides 440 by 100 and gets 4.4. If glucose is less than or equal to the target, the increment should be zero, not negative, because the hyperglycemia correction is not meant to subtract sodium for normal or low glucose values.

The Katz calculation adds 1.6 mEq/L for every 100 mg/dL increment. In the example, 1.6 times 4.4 is 7.04. Adding 7.04 to the measured sodium of 128 gives 135.04 mEq/L. The Hillier calculation uses 2.4 instead of 1.6. With the same increment, 2.4 times 4.4 is 10.56. Adding 10.56 to 128 gives 138.56 mEq/L.

The difference between 135.04 and 138.56 is not rounding error; it is formula selection. That is why the output should include the factor name. For implementation, a correctionFactor input can be stored as 1.6 or 2.4, and the formula can be generalized as measured sodium plus correction factor times glucose increment. A both-mode should run the generalized formula twice and return both labeled outputs.

Effective osmolality is separate. A common estimate is two times measured sodium plus glucose divided by 18. The example is 2 times 128 plus 30, or 286 mOsm/kg. Urea is excluded from effective osmolality because it crosses cell membranes more freely and is not an effective osmole in the same way for tonicity. The calculator should label this as an estimate and should not substitute it for a measured osmolality result when one is available.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Kashyap, A.S. (1999). Hyperglycemia-Induced Hyponatremia: Is It Time to Correct the Correction Factor? JAMA Internal Medicine.
2. [2]Hillier, T.A., Abbott, R.D., and Barrett, E.J. (1999). Hyponatremia: evaluating the correction factor for hyperglycemia. American Journal of Medicine.
3. [3]Wolf, M.B. (2017). Hyperglycemia-induced hyponatremia: Reevaluation of the Na+ correction factor. Journal of Critical Care.
4. [4]Ing, T.S. et al. (2020). The Corrected Serum Sodium Concentration in Hyperglycemic Crises: Computation and Clinical Applications. Frontiers in Medicine.
5. [5]Milanesi, A., Bhat, S., and Weinreb, J.E. (2026). Hyperglycemic Hyperosmolar Syndrome. Endotext, NCBI Bookshelf.
6. [6]Gosmanov, A.R., Gosmanova, E.O., and Kitabchi, A.E. (2021). Hyperglycemic Crises: Diabetic Ketoacidosis and Hyperglycemic Hyperosmolar State. Endotext PDF.