Corrected sodium calculator for hyperglycemia
Correct a measured serum sodium for high glucose with both published factors, Katz 1973 (1.6 mmol/L per 100 mg/dL) and Hillier 1999 (2.4 mmol/L per 100 mg/dL): enter sodium and glucose in mg/dL or mmol/L and see the two corrected values side by side.
Guides
- Katz vs Hillier: which sodium correction factor for hyperglycemia?Katz 1.6 or Hillier 2.4? Where each sodium correction factor for hyperglycemia comes from, which to use, and how to read corrected sodium in DKA and HHS.
How this corrected sodium calculator works
This corrected sodium calculator estimates what a patient's serum sodium would be if their glucose were 100 mg/dL (5.6 mmol/L), using the two correction factors in common use. When insulin is lacking, glucose that builds up in the extracellular fluid draws water out of cells, and that water dilutes the sodium. The 2009 American Diabetes Association consensus statement on hyperglycemic crises explains that the admission sodium in diabetic ketoacidosis is usually low for exactly this reason. M. A. Katz, writing in the New England Journal of Medicine in 1973, calculated an expected fall of 1.6 mmol/L in sodium for every 100 mg/dL rise in glucose. In 1999 Hillier and colleagues at the University of Virginia tested this directly in 6 healthy volunteers and measured an average fall of 2.4 mmol/L per 100 mg/dL. The calculator applies both factors to the glucose above 100 mg/dL and adds the result to the measured sodium, so you can see how far apart the two estimates are.
Katz (1973): corrected Na = measured Na + 1.6 × (glucose − 100) ÷ 100
Hillier (1999): corrected Na = measured Na + 2.4 × (glucose − 100) ÷ 100
Sodium in mmol/L (the same number as mEq/L), glucose in mg/dL. Glucose in mmol/L is converted first with mg/dL = mmol/L × 18, the factor the 2009 ADA statement uses in its osmolality formula, so each factor works out to about 0.29 (Katz) or 0.43 (Hillier) mmol/L of sodium per 1 mmol/L of glucose above 5.6. At or below 100 mg/dL no correction is added.
The calculator shows both results to one decimal place, along with how much each factor added. Sodium and glucose should come from the same blood sample, because glucose can change quickly during treatment.
Corrected sodium results and what they mean
A corrected sodium result is read against the usual serum sodium reference range, which MedlinePlus gives as 135 to 145 mEq/L, while noting that ranges vary slightly between laboratories. The European hyponatraemia guideline of 2014 defines hyponatraemia as a serum sodium below 135 mmol/L. When the measured sodium is low but the corrected sodium is in the normal range, the low reading is explained by the glucose, a hyperglycemia-induced hyponatremia in the words of Katz's title, rather than by an excess of water alone. When the corrected sodium is above 145 mmol/L, the patient has lost more water than sodium. The 2009 ADA consensus statement puts it plainly: an increased or even normal serum sodium in the presence of hyperglycemia indicates a profound loss of water. A corrected sodium that stays below 135 mmol/L points to a true sodium deficit or water excess on top of the glucose effect.
| Corrected sodium | Band | What it suggests with hyperglycemia |
|---|---|---|
| Below 135 mmol/L | Low | Hyponatremia remains after the glucose effect is removed: a sodium deficit or water excess as well. |
| 135–145 mmol/L | Normal | The low measured sodium is accounted for by the glucose (hyperglycemia-induced hyponatremia). |
| Above 145 mmol/L | High | Water loss greater than sodium loss; in hyperglycemic crises, a profound water deficit. |
When the two factors land in different bands, as in the default example, both are shown on the bar. That disagreement is common at very high glucose, because the gap between the factors grows by 0.8 mmol/L for every 100 mg/dL.
Katz or Hillier: which corrected sodium factor to trust
Choosing between the Katz and Hillier corrected sodium factors matters most when glucose is very high. Katz's 1.6 factor came from a calculation, as the title of his 1973 letter says, and Hillier's team noted in 1999 that no controlled experimental data had tested it. Hillier suppressed insulin with somatostatin in 6 healthy subjects, raised their glucose above 600 mg/dL within an hour by infusing dextrose, and measured sodium every 10 minutes. The mean fall was 2.4 mmol/L per 100 mg/dL, significantly greater than 1.6 (P = 0.02). The relation was also not linear: up to 400 mg/dL the 1.6 factor worked well, but above 400 mg/dL a factor of 4.0 fitted better. Hillier concluded that 2.4 is a better overall estimate than 1.6. Even so, the ADA consensus statements of 2009 and 2024 both still describe the 1.6 figure, so many hospital protocols are written around Katz.
The guide Katz vs Hillier goes through both papers, how each factor reads in DKA and HHS, and worked examples.
When corrected sodium is less accurate
A corrected sodium value is an estimate built on a single average factor, and several things make it less reliable. Hillier's 1.6 versus 2.4 debate rests on 6 healthy volunteers whose glucose was raised over about an hour, not on patients with days of osmotic diuresis, vomiting or kidney disease. Moran and Jamison argued in 1985 that the sodium response to hyperglycemia is variable rather than fixed, because it depends on how body water and solute are distributed, on how much solute cells lose as extracellular glucose rises, and on what the patient has taken in and lost. Hillier also found the relation nonlinear above 400 mg/dL, so a straight-line factor can under-correct there. Finally, the measured sodium itself can be misleading: the 2009 ADA statement notes that pseudohyponatremia, a falsely low sodium reading, may occur in DKA with severe chylomicronemia.
Corrected sodium is a way of reading a sodium result, not a separate measurement, and it does not replace repeated measured values as glucose changes. It also does not enter the effective osmolality formula, which the 2009 ADA statement writes with the measured sodium: 2 × measured Na + glucose (mg/dL) ÷ 18.
Questions
What is the formula for corrected sodium?
Corrected Na = measured Na + 1.6 × (glucose − 100) ÷ 100 by Katz, or + 2.4 × (glucose − 100) ÷ 100 by Hillier, with sodium in mmol/L and glucose in mg/dL.
How do I correct sodium when glucose is in mmol/L?
Multiply glucose by 18 to get mg/dL and use the same formula, or add about 0.29 (Katz) or 0.43 (Hillier) mmol/L of sodium for each 1 mmol/L of glucose above 5.6. A glucose of 33.3 mmol/L with a sodium of 128 gives 136.0 (Katz) or 140.0 (Hillier).
Which correction factor should I use?
The ADA consensus statements describe 1.6; Hillier's 1999 experiment found 2.4 a better overall estimate and 1.6 accurate only up to about 400 mg/dL. This calculator shows both so you can see whether the choice changes the band. The Katz vs Hillier guide compares them in detail.
Is corrected sodium used in the osmolality calculation?
No. The 2009 ADA statement calculates effective serum osmolality from the measured sodium: 2 × measured Na + glucose (mg/dL) ÷ 18. Using the corrected sodium there would count the glucose effect twice.
Is my data sent anywhere?
No. The calculation runs in your browser, and the values you enter are not sent or stored.
Sources
- Katz MA. Hyperglycemia-induced hyponatremia—calculation of expected serum sodium depression. N Engl J Med. 1973;289(16):843–844. doi:10.1056/NEJM197310182891607
- Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. Am J Med. 1999;106(4):399–403. doi:10.1016/S0002-9343(99)00055-8
- Kitabchi AE, Umpierrez GE, Miles JM, Fisher JN. Hyperglycemic crises in adult patients with diabetes. Diabetes Care. 2009;32(7):1335–1343. doi:10.2337/dc09-9032
- Umpierrez GE, Davis GM, ElSayed NA, et al. Hyperglycaemic crises in adults with diabetes: a consensus report. Diabetologia. 2024;67(8):1455–1479. doi:10.1007/s00125-024-06183-8
- Moran SM, Jamison RL. The variable hyponatremic response to hyperglycemia. West J Med. 1985;142(1):49–53. PubMed 3976219
- Spasovski G, Vanholder R, Allolio B, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol. 2014;170(3):G1–G47. doi:10.1530/EJE-13-1020
- MedlinePlus. Sodium blood test. U.S. National Library of Medicine. medlineplus.gov/ency/article/003481.htm