1Sodium Correction Formulas & Osmotic Shift
• Katz Factor (1.6): Corrected Na = Measured Na + 1.6 × (Glucose (mg/dL) − 100) / 100
• Hillier Factor (2.4): Corrected Na = Measured Na + 2.4 × (Glucose (mg/dL) − 100) / 100 (Recommended for glucose > 400 mg/dL).
• Note: For SI units (mmol/L), multiply glucose by 18 to convert to mg/dL before applying the formula.
2Clinical Implications in DKA and HHS
Severe hyperglycemia exerts osmotic pressure that pulls water across cell membranes from the intracellular to the extracellular space, artificially diluting serum sodium concentration. The measured sodium is thus deceptively low. Corrected sodium reveals the true underlying electrolyte status, which dictates fluid selection during resuscitation:
- Diabetic Ketoacidosis (DKA): A corrected sodium > 135 mmol/L indicates underlying hypernatremia that will become unmasked as serum glucose is lowered by insulin therapy.
- Hyperglycemic Hyperosmolar State (HHS): Corrected sodium is frequently markedly elevated (> 145 mmol/L), guiding the prompt transition from 0.9% Normal Saline to 0.45% Saline after initial circulatory stabilization.
Which Formula to Use?
Use Hillier (2.4) for glucose >400 mg/dL (22 mmol/L) — this is now preferred in most guidelines. Use Katz (1.6) for moderate hyperglycaemia (180–400 mg/dL). Both formulas are presented in the result — the Hillier corrected Na is often the clinically more relevant value in severe hyperglycaemia such as HHS.
3Frequently Asked Questions
Which correction factor should I use — Katz (1.6) or Hillier (2.4)?+
While Katz (1.6) is historically traditional, prospective studies by Hillier et al. demonstrated that sodium drops by approximately 2.4 mmol/L per 100 mg/dL glucose elevation when glucose exceeds 400 mg/dL. Hillier (2.4) is therefore more accurate in severe hyperglycemia (HHS).
What is the maximum safe correction rate for hyponatremia?+
For chronic hyponatremia, sodium should be corrected by no more than 10 to 12 mmol/L per 24 hours (and ≤8 mmol/L in high-risk patients) to prevent Osmotic Demyelination Syndrome (central pontine myelinolysis).
What is Osmotic Demyelination Syndrome (ODS)?+
ODS is a devastating neurological condition caused by rapid osmotic shifts when chronic hyponatremia is corrected too aggressively. Brain cells lose osmolytes to adapt to low sodium; rapid sodium elevation shrinks brain cells, leading to demyelination of the pons and extrapontine structures.
Clinical Takeaway: Never rely solely on measured sodium in severe hyperglycemia. Always calculate corrected sodium to anticipate fluid shifts during insulin therapy.
Medical Disclaimer: This calculator provides decision-support estimates for qualified healthcare professionals. Electrolyte management in DKA and HHS requires frequent serial lab monitoring and clinical correlation.