Corrected sodium is an estimate used when hyperglycaemia (hyperglycemia) has lowered the measured serum sodium through an osmotic water shift. It does not replace the measured sodium, serum osmolality or the wider assessment of a patient with hyperglycaemia. Use the calculator for the arithmetic; use this Guide to understand what the corrected value is trying to represent.
Why can high glucose lower the measured sodium?
When extracellular glucose rises markedly, water shifts from the intracellular space into the extracellular space. That added extracellular water can dilute the measured sodium concentration. As glucose falls, water can move back into cells and the measured sodium may rise even when no sodium has been added.
This is a real translocational water shift. It is different from pseudohyponatraemia, which can be an indirect ion-selective electrode (ISE) measurement artefact in the presence of very high lipids or proteins. If that artefact is suspected, verify the sodium measurement method or a direct ISE result; applying a glucose correction to a spuriously low sodium does not repair the laboratory artefact.
What does corrected sodium estimate?
The conventional corrected value estimates sodium after glucose is mathematically brought to about 100 mg/dL while body water, sodium and potassium are otherwise assumed unchanged. It is therefore a calculated estimate, not another directly measured electrolyte result or a literal forecast of the next sodium during treatment.
Think of the two numbers as answering different questions.
- Measured sodium: what the laboratory measured at that time.
- Corrected sodium: an estimate after mathematically accounting for hyperglycaemia.
Why are there 1.6 and 2.4 correction factors?
Murray Katz described the classic estimate that sodium changes by about 1.6 mmol/L for each 100 mg/dL change in glucose. Hillier and colleagues later tested the relationship in only six healthy subjects. They reported 2.4 mmol/L per 100 mg/dL as the better overall estimate; 1.6 worked reasonably up to about 400 mg/dL, while a factor around 4.0 fit the higher-glucose portion of that experiment better.
That is why MedMaths allows the user to select Katz or Hillier rather than presenting one coefficient as an exact biological constant. The approximately 4.0 observation is included as study context only; MedMaths does not turn it into a third universal high-glucose pathway.
Which correction factor should you use?
Use the method required by the current clinical source or local protocol.
If the source does not specify a method, the choice should not be made simply because one value looks more reassuring. The two equations are estimates derived from different evidence and can diverge materially as glucose rises.
The 2024 international consensus report on adult hyperglycaemic crises describes an approximately 1.6 mmol/L rise in sodium for each 100 mg/dL fall in glucose during HHS treatment, while emphasising serial assessment of glucose, sodium, osmolality and the overall clinical response. A 2024 RCPA comparison also found that equation choice can materially change sodium classification at higher glucose and did not establish one correction equation as clinically superior.
Corrected sodium is not serum osmolality
Corrected sodium and serum osmolality are related to hyperglycaemic water balance, but they are not interchangeable calculations. Corrected sodium adjusts the sodium estimate for glucose. Calculated serum osmolality estimates the concentration of major osmotically active solutes, while measured osmolality comes from laboratory osmometry.
If the clinical question is about total osmolality or an osmol gap, use the Serum Osmolality Calculator and the Calculated Serum Osmolality and Osmol Gap Guide rather than treating corrected sodium as a substitute.
What are the main limitations?
- The correction factor is an estimate, not an exact patient-specific constant.
- The Katz and Hillier relationships were derived from different evidence and can produce different results.
- The conventional construct assumes glucose is normalised while body water, sodium and potassium are otherwise unchanged. Real DKA/HHS is an open system, so osmotic diuresis, fluids, insulin and electrolyte changes can alter subsequent measured sodium.
- Marked volume disturbance, renal losses and ongoing treatment can change the sodium-glucose relationship over time.
- A corrected value should not be used on its own to select fluids or manage a hyperglycaemic emergency.
- Measured sodium, glucose and other laboratory values should ideally come from the same clinical time point.
What should you do with the number?
Treat corrected sodium as one piece of the assessment. Keep the measured sodium visible, note which correction factor was used, and interpret the estimate alongside glucose, measured or calculated osmolality, fluid status and the relevant hyperglycaemia protocol.
Sources
- Katz MA. Hyperglycemia-induced hyponatremia — calculation of expected serum sodium depression.
- Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia.
- The Corrected Serum Sodium Concentration in Hyperglycemic Crises: Computation and Clinical Applications.
- 2024 international consensus report: Hyperglycemic Crises in Adults With Diabetes.
- Lam Q, Wijeratne N. Comparison of commonly used equations for sodium adjustment in hyperglycaemia. Pathology. 2024.
- Ing TS et al. Pseudohyponatremia: Mechanism, Diagnosis, Clinical Associations and Management. 2023.
- American Diabetes Association. Diabetes Care in the Hospital: Standards of Care in Diabetes—2026.