Corrected Sodium Calculator

Background.

A patient arrives in diabetic ketoacidosis with a serum sodium of 128 mEq/L and a glucose of 540 mg/dL. Is the sodium really low, or is the glucose pulling it down? Corrected sodium answers that by estimating what the sodium would read if the glucose were back to normal. Here the answer is 135.04 mEq/L by the Katz factor and 138.56 mEq/L by the Hillier factor, and both figures appear side by side.

The effect is real dilution, not a laboratory artifact. When insulin is lacking, glucose builds up in the extracellular fluid and cannot readily enter cells, so it acts as an osmole: water moves out of the cells into the blood and interstitial fluid, and the sodium dissolved there is diluted. As treatment brings the glucose down, that water returns to the cells and the measured sodium rises. Corrected sodium is a forecast of where it is heading.

Two correction factors are in common use, and they disagree. The traditional figure, published by Katz in 1973, adds 1.6 mEq/L of sodium for every 100 mg/dL of glucose above normal. Hillier and colleagues, raising glucose experimentally in healthy volunteers in 1999, measured a larger average fall and proposed 2.4 mEq/L, noting that the relationship steepens at higher glucose levels. Showing both values keeps that uncertainty visible instead of hiding it inside a single number; the gap between them widens by 0.8 mEq/L for every further 100 mg/dL of glucose.

An effective osmolality estimate, twice the measured sodium plus the glucose in mmol/L, is shown alongside and can be switched off.

The arithmetic supports clinical judgment; it does not replace it. Fluid choice, the pace of sodium change and the diagnosis of any underlying sodium disorder depend on volume status, kidney function, measured osmolality, acid-base findings and how the patient responds to treatment, and belong to the treating team and local protocols.

What is corrected sodium calculator?

Corrected sodium is a calculated estimate of the serum sodium concentration that would remain once a high blood glucose had returned to a reference level, conventionally 100 mg/dL. It strips out the dilution caused by water shifting out of cells under the osmotic pull of glucose, so that what is left reflects the patient's underlying balance of sodium and water. A corrected sodium that is still low points to a sodium or water disorder beyond the hyperglycemia; one that is high suggests the high glucose is masking a water deficit. The measured value is not wrong, and nothing in the calculation implies it is: it is the true concentration at that moment, and the corrected figure is a projection from it.

Two forces act on sodium during a hyperglycemic crisis, and they pull in opposite directions. The water shift out of cells lowers the measured sodium within hours. Meanwhile glucose spilling into the urine drags water with it, an osmotic diuresis that loses proportionally more water than sodium, which pushes the underlying sodium up over days. The measured value is the net of both; the corrected value removes the first so the second can be seen.

How to use this calculator.

1. 01Enter the measured serum sodium in mEq/L (numerically the same as mmol/L), taken from the same blood sample as the glucose if possible.
2. 02Enter the serum glucose and set the unit to match your laboratory report: mg/dL as used in the United States, or mmol/L as used in most other countries. Values in mmol/L are multiplied by 18 before the correction, and the converted figure appears among the results.
3. 03Leave the target glucose at 100 mg/dL unless your protocol names a different reference. It is always entered in mg/dL, even when the measured glucose is in mmol/L; 100 mg/dL is about 5.6 mmol/L.
4. 04Keep the effective osmolality toggle on if you want that estimate as well; switching it off shows 0 in its place.
5. 05Read the Katz and Hillier values together. When they fall on different sides of a threshold that matters to the decision in front of you, that disagreement is itself information, and a measured osmolality or a repeat sodium as glucose falls will settle more than either formula can.

The formula.

The calculation first puts glucose in mg/dL: a value entered in mmol/L is multiplied by 18, which is the molar mass of glucose, 180 g/mol, rescaled from litres to decilitres. It then counts how many hundreds of mg/dL the glucose stands above the target: increment = (glucose − target) ÷ 100. If the glucose is at or below the target the increment is set to zero, so the correction never subtracts sodium.

The two corrected values follow directly. Katz: Na corrected = Na measured + 1.6 × increment. Hillier: Na corrected = Na measured + 2.4 × increment. Each factor is in mEq/L of sodium per 100 mg/dL of glucose. Because both scale with the glucose excess, a glucose of 200 mg/dL moves the sodium by only 1.6 or 2.4 mEq/L, while at 1,100 mg/dL the corrections are 16 and 24 mEq/L and the two answers sit 8 mEq/L apart.

The factors come from different reasoning. Katz derived 1.6 from a theoretical model of how much water would leave cells for a given rise in extracellular glucose. Hillier's group measured the actual fall in sodium as they drove glucose up in volunteers whose own insulin was suppressed, and found that a single factor of 2.4 described the data better overall, with the true slope smaller at modest glucose levels and larger at very high ones. Neither factor accounts for the patient's starting water balance, ongoing losses or the fluids already given, which is why serial measured values during treatment outrank any single correction.

Effective osmolality, also called tonicity, is estimated as 2 × measured sodium + glucose in mmol/L. Sodium is doubled to account for its accompanying anions, mainly chloride and bicarbonate. Urea is left out deliberately: it crosses cell membranes freely, so although it raises total osmolality it does not draw water out of cells. The estimate uses the measured sodium, not a corrected one, because it describes the fluid as it is now.

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.