Estimate corrected serum sodium when glucose is elevated. Enter measured sodium (mEq/L) and plasma glucose (mg/dL). Both the Katz 1973 and Hillier 1999 correction factors are shown.
Katz 1973 formula: corrected Na = measured Na + 0.016 x (glucose - 100). Hillier 1999 variant uses 0.024. Both are shown below.
Normal sodium reference range is 135 to 145 mEq/L. This calculator applies the correction for hyperglycemia only. It does not diagnose or treat any condition.
High plasma glucose draws water out of cells and into the bloodstream, diluting serum sodium. The sodium measured by the lab in that setting is lower than the patient's true sodium at normal glucose. The correction formula estimates what sodium would be if glucose were at a normal baseline of 100 mg/dL.
For example: measured sodium 130 mEq/L, glucose 400 mg/dL. Katz: 130 + 0.016 x (400 - 100) = 130 + 4.8 = 134.8 mEq/L. Hillier: 130 + 0.024 x 300 = 130 + 7.2 = 137.2 mEq/L. The difference can be clinically meaningful at high glucose levels.
The 0.016 factor (Katz 1973) appears in many textbooks and is the most widely cited. The 0.024 factor (Hillier 1999) is supported by a laboratory study that measured the actual change in sodium at multiple glucose concentrations. Several references note that the Katz formula underestimates the correction at severe hyperglycemia. This calculator shows both values. The choice is a clinical judgment.
Original formula: Katz MA. "Hyperglycemia-Induced Hyponatremia: Calculation of Expected Serum Sodium Depression." New England Journal of Medicine, 1973;289(16):843-844. Revised coefficient: Hillier TA, Abbott RD, Barrett EJ. "Hyponatremia: evaluating the correction factor for hyperglycemia." American Journal of Medicine, 1999;106(4):399-403. See the MDCalc sodium correction reference for further context.
Hyperglycemia and sodium disorders frequently coexist with kidney disease. See the GFR Calculator (CKD-EPI 2021) for kidney function estimation and the Corrected Calcium Calculator for another common electrolyte correction used in the same setting.
The Katz 1973 formula is: corrected sodium (mEq/L) = measured sodium + 0.016 x (glucose - 100). A variant published by Hillier and colleagues in 1999 uses a coefficient of 0.024 instead of 0.016. The Hillier factor may give a closer estimate at very high glucose levels.
High glucose draws water from cells into the extracellular space by osmosis. This additional water dilutes plasma sodium, making the measured sodium appear lower than it would be at normal glucose. When glucose returns to normal, sodium rises back toward its corrected value.
The 0.016 factor (Katz 1973) is historically the most widely cited. The 0.024 factor (Hillier 1999) was derived from a study showing the Katz factor may underestimate the correction at very high glucose levels. This calculator shows both. Which to apply is a clinical decision.
Normal serum sodium is generally 135 to 145 mEq/L. Values below 135 are hyponatremia and above 145 are hypernatremia. In hyperglycemia, measured sodium may be artificially low, so the corrected value helps assess whether true hyponatremia exists.