π§ Sodium Correction Calculator
The true sodium level hiding behind high blood sugar.
Corrected serum sodium
For informational purposes only, not medical advice.
Corrected sodium equals measured sodium plus 1.6 times (glucose minus 100) divided by 100. When blood sugar climbs, glucose pulls water from cells into the bloodstream and dilutes the sodium reading, so a lab value of 128 mEq/L at a glucose of 400 mg/dL is really about 132.8 mEq/L once the dilution is removed. That gap changes treatment, which is why clinicians correct first and react second.
This page runs the Katz correction from 1973, the formula still taught in medical schools and used on wards. Type in the two lab numbers and you get the corrected sodium instantly, plus how much the correction added and whether the result sits in the normal 135 to 145 mEq/L band.
How to Use This Calculator
Pull the two numbers from the same blood draw: serum sodium in mEq/L and glucose in mg/dL. The correction only makes sense when both come from the same sample, because glucose shifts hour by hour. Enter them above and the corrected value appears on its own.
Enter the measured serum sodium exactly as the lab reported it, in mEq/L (numerically the same as mmol/L for sodium).
Enter the glucose from the same draw in mg/dL. If your lab reports mmol/L, multiply by 18 first.
Read the corrected sodium, the size of the correction, and the interpretation band. A correction near zero at normal glucose means the measured value was already the true value.
The Katz Formula
Each 100 mg/dL of glucose above 100 adds about 1.6 mEq/L back to the sodium. The physiology is simple dilution: glucose cannot freely cross cell membranes the way water can, so high extracellular glucose draws water out of cells, expanding the extracellular space and lowering the measured sodium concentration. None of the body's sodium went anywhere. The formula just reverses the arithmetic of that water shift.
One honest caveat: some clinicians use 2.4 instead of 1.6 when glucose tops 400 mg/dL, following Hillier's later work. The difference is small at moderate glucose levels and the 1.6 version remains the standard default. If your glucose is extremely high, treat the corrected value as an estimate and let the treating team pick the factor they trust.
Worked Example
A patient arrives with a measured sodium of 128 mEq/L and a glucose of 400 mg/dL. Subtract 100 from the glucose to get 300, divide by 100 to get 3, and multiply by 1.6 to get a correction of 4.8 mEq/L. Add that to 128 and the corrected sodium is 132.8 mEq/L.
Notice what changed: the raw number screams moderate hyponatremia, but the corrected number is only mildly low. Treating the 128 aggressively with hypertonic saline would overshoot the true deficit. This is exactly the trap the formula exists to prevent, and it is why the corrected value, not the measured one, guides fluid decisions in hyperglycemic patients.
Reading Your Result
The corrected sodium reads on the same scale as any sodium result, because it is one. Use the standard bands:
| Corrected sodium | Meaning |
|---|---|
| Below 135 mEq/L | Hyponatremia, true, not just dilutional. Workup depends on volume status and cause. |
| 135 to 145 mEq/L | Normal. The low measured value was dilution from glucose alone. |
| Above 145 mEq/L | Hypernatremia. The patient is short on water relative to sodium, and the glucose was masking it. |
My rule: when the correction is large, say more than 5 mEq/L, recheck both numbers after glucose comes down. The formula assumes a steady state, and a crashing glucose during treatment moves the target while you aim at it.
When the Formula Does Not Apply
Only use this correction for hyperglycemia. It does not fix pseudohyponatremia from very high triglycerides or paraproteins, which is a lab artifact of a different kind and needs direct measurement by a different method. It also does not apply when glucose is normal or low: at a glucose of 90, the formula subtracts a hair and returns basically the measured value, which is correct behavior, not a bug.
Severe hyperglycemia above 600 mg/dL stretches the linear assumption, and DKA adds an acidosis-driven shift of its own. In those settings the corrected sodium is a starting estimate for discussion with the medical team, not a number to act on alone. Recheck early and often.
Related Tools
Sodium and water balance travel together. Once you have the corrected value, our sodium deficit calculator estimates the replacement amount for true hyponatremia, the daily water intake calculator sets a sensible hydration baseline, and the blood pressure checker puts the sodium story next to the pressure it influences.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is corrected sodium?
Corrected sodium is the serum sodium adjusted for the diluting effect of high blood sugar. Glucose pulls water into the bloodstream, which lowers the measured sodium without changing total body sodium. The Katz formula adds back about 1.6 mEq/L for every 100 mg/dL of glucose above 100, revealing the true sodium level.
Why does high blood sugar lower sodium?
Glucose stays mostly outside cells, and water follows it by osmosis. As glucose rises, water shifts from inside cells to the bloodstream, diluting everything dissolved there, including sodium. Correct the glucose and the water shifts back, which is why the sodium often normalizes on its own as sugar is treated.
Should I use 1.6 or 2.4 as the correction factor?
Use 1.6 as the default; it is the Katz factor from 1973 and remains the standard. Hillier proposed 2.4 for glucose above 400 mg/dL. At a glucose of 300 the two factors differ by only 1.6 mEq/L, so either is reasonable. For very high glucose, ask the treating clinician which factor their protocol uses.
Are mEq/L and mmol/L the same for sodium?
Yes, numerically. Sodium has a valence of 1, so 1 mmol/L equals 1 mEq/L. Labs report either unit and the formula works identically with both. Just keep glucose in mg/dL; if your lab reports glucose in mmol/L, multiply by 18 before entering it.
Does the formula work when glucose is normal?
It returns essentially the measured value, which is the right answer. At a glucose of 100 the correction is zero, and near 100 it is a fraction of a point. There is nothing to correct when there is no dilution, so a normal glucose with low sodium means true hyponatremia that needs its own workup.
What is pseudohyponatremia?
A falsely low sodium caused by the lab method when blood is crowded with triglycerides or abnormal proteins. The sodium in the water portion of blood is actually normal. This calculator does not correct for it; that artifact needs direct ion-selective measurement, usually on a blood gas analyzer.
How often should corrected sodium be rechecked?
As often as glucose is rechecked during treatment, typically every few hours in DKA or HHS protocols. The correction is a snapshot: falling glucose shrinks the correction in real time, so a value that looked fine an hour ago can become truly low as sugar drops.
Can I use this for low blood sugar?
There is no correction to apply. Hypoglycemia does not dilute sodium, so the measured value stands. The formula would subtract a tiny amount below a glucose of 100, which has no physiologic meaning; just read the lab value as reported.
Does correcting sodium change the treatment?
Often, yes. A measured 128 that corrects to 136 needs no sodium replacement at all, while a measured 128 that corrects to 128 is real hyponatremia. Acting on the uncorrected number risks overcorrection, which carries its own danger, so guidelines teach correcting first.
Who should not rely on this calculator?
Anyone making treatment decisions without a clinician. This is an educational tool that reproduces a standard formula; it cannot weigh volume status, kidney function, or the cause of the hyperglycemia. Share the result with the medical team and let them decide what it means for care.