Correct serum sodium for hyperglycaemia-induced dilutional hyponatraemia (e.g., DKA, HHS).
When to use: Apply corrected sodium in DKA and HHS (Hyperosmolar Hyperglycaemic State) where profound hyperglycaemia draws water from cells into the intravascular space, diluting sodium. A patient with glucose 600 mg/dL and Na 130 mEq/L actually has a corrected Na of ~138 mEq/L (true normonatraemia). Use this to correctly assess fluid status and guide safe insulin and fluid therapy to avoid cerebral oedema from overly rapid osmolarity correction.
Calculator
Enter >100 mg/dL (baseline). Most useful when glucose >200 mg/dL.
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Formula
Corrected Na = Measured Na + 1.6 × [(Glucose mg/dL − 100) / 100]
Normal: 135–145 mEq/L
Alternative: Hillier correction uses 2.4 per 100 mg/dL above 100 (more accurate in severe hyperglycaemia)
Key Points for NEET PG
For every 100 mg/dL glucose above 100, serum Na falls by ~1.6 mEq/L (Katz correction) due to osmotic water shift.
Hillier correction factor (2.4 mEq/L per 100 mg/dL) is more accurate for severe hyperglycaemia (glucose >400 mg/dL).
HHS (Hyperosmolar Hyperglycaemic State): glucose >600 mg/dL, osmolality >320 mOsm/kg, corrected Na often very high (true hypernatraemia): target of fluid therapy.
DKA: corrected Na helps assess true sodium status to guide safe fluid therapy and prevent cerebral oedema during insulin therapy.
