Corrected Sodium Calculator
Estimate sodium corrected for high glucose with the Katz or Hillier rule in mEq/L.
What it does
High glucose pulls water out of cells and into the blood, which dilutes sodium on the lab report. The measured number looks lower than the body really is, so clinicians estimate a corrected value before acting on it.
Two rules dominate. Katz 1973 adds 1.6 mEq/L of sodium for every 100 mg/dL of glucose above normal. Hillier 1999 uses 2.4 per 100 mg/dL, which tracks severe hyperglycemia more closely in later studies.
The tool above takes both numbers and returns the corrected sodium, the shift from the measured value, and the rule used. The default 130 mEq/L at 600 mg/dL gives 138 mEq/L with Katz and 142 mEq/L with Hillier.
The correction is a dilution model: it answers what sodium would read once glucose falls toward normal, not what the total body sodium deficit is. Sodium still has to be interpreted with the clinical picture, medications, and fluid balance.
Metric glucose in mmol/L uses 5.55 as the normal midpoint instead of 100 mg/dL. Every 5.55 mmol/L above that shifts sodium the same 1.6 or 2.4 mEq/L, so both systems land on identical corrections. This page covers the formula, a hand checked example, a reference table at several glucose levels, and practice checks, all strictly educational.
How to use
- Pick mg/dL or mmol/L for glucose.
- Choose the Katz or Hillier rule.
- Enter the measured sodium from the lab.
- Enter the glucose drawn at the same time.
- Read the corrected sodium and the change.
- Repeat after treatment to watch the trend.
Formula
- sodium
- Measured sodium in mEq/L, usually from the same draw as glucose.
- glucose
- Serum glucose in mg/dL (or mmol/L with a 5.55 midpoint).
- k
- Sodium shift per 100 mg/dL of glucose excess: 1.6 (Katz) or 2.4 (Hillier).
Both rules pivot at a glucose of 100 mg/dL: readings above that reduce measured sodium, readings below it raise it. The metric form divides the glucose gap by 5.55 mmol/L per unit. Published labs vary in which constant they cite, and modern reviews note the real relationship is not perfectly linear, so treat the result as an estimate with wide error bars at extreme glucose values.
Worked example
Example: sodium 130, glucose 600
Measured sodium 130 mEq/L with glucose 600 mg/dL (defaults).
- Glucose sits 600 minus 100, or 5 hundreds, above the midpoint.
- Katz: 130 + 1.6 x 5 = 130 + 8 = 138 mEq/L, a +8 shift.
- Hillier: 130 + 2.4 x 5 = 130 + 12 = 142 mEq/L, a +12 shift.
- Metric mirror: 33.3 mmol/L is 5 gaps of 5.55 above normal, same shifts.
- Tool shows 138 mEq/L (+8) for Katz and 142 mEq/L (+12) for Hillier.
Reference table
| Glucose (mg/dL) | Katz | Hillier |
|---|---|---|
| 100 | 130 mEq/L | 130 mEq/L |
| 200 | 131.6 mEq/L | 132.4 mEq/L |
| 400 | 134.8 mEq/L | 137.2 mEq/L |
| 600 | 138 mEq/L | 142 mEq/L |
| 800 | 139.2 mEq/L | 146.8 mEq/L |
Limits
- Built for hyperglycemic states like DKA and HHS, not steady outpatient numbers.
- A model, not a measurement. Real sodium also moves with fluids, ketones, and time.
- Glucose below 100 mg/dL pushes the correction negative, which is rarely meaningful.
- Lab method (indirect vs direct ion-sensitive electrode) changes measured sodium before any math.
Common mistakes
- Using the Hillier constant while quoting Katz, or the reverse.
- Pivoting at zero glucose instead of the 100 mg/dL midpoint.
- Reading the corrected value as the treatment target rather than context.
- Comparing numbers drawn hours apart, since glucose and sodium both drift.
- Ignoring the lab method, which can shift measured sodium by several mEq/L.
Try it yourself
Quick checks. Answers sit tucked under each question.
Sodium 128 at glucose 800 mg/dL with Katz?
139.2 mEq/L, a +11.2 shift.
Sodium 140 at glucose 400 mg/dL with Hillier?
147.2 mEq/L, a +7.2 shift.
Sodium 130 at glucose 11.1 mmol/L with Katz?
131.6 mEq/L, a +1.6 shift.
Questions
Why correct sodium at all?
Glucose holds water in the blood and dilutes sodium. The corrected value estimates what sodium would read once glucose settles toward normal.
Katz or Hillier?
Katz 1973 with 1.6 mEq per 100 mg/dL remains the classic teaching rule. Hillier 1999 with 2.4 fits severe hyperglycemia better in later validation work.
What is a normal sodium?
Roughly 135 to 145 mEq/L. Single readings need context; trends over time carry more signal.
Why 100 mg/dL as the midpoint?
Both published rules anchor the correction there, so only glucose above that threshold lowers the measured value.
Is this pseudohyponatremia?
No. High lipids or protein cause pseudohyponatremia by lab artifact. High glucose causes dilutional hyponatremia, which is what these rules model.
Can I use it in DKA?
The rule estimates the glucose-adjusted level often quoted during DKA care, but real management needs clinicians, fluids, and insulin. Educational only.
Sources
- RCPA pathology journal review of sodium correction equations
- Hillier et al 1999: hyponatremia correction in hyperglycemia (PubMed 10225241)
- Katz 1973, New England Journal of Medicine