Laboratory & Electrolytes

Corrected Sodium for Hyperglycaemia

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

Measured Serum Sodium(mEq/L)

Serum Glucose(mg/dL)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.
Osmolality formula: 2×Na + glucose/18 + BUN/2.8 — serum osmolality >320 mOsm/kg = hyperosmolar state.

References

Katz MA. Hyperglycemia-induced hyponatremia — calculation of expected serum sodium depression · N Engl J Med (1973)

Hillier TA et al. Hyponatremia: evaluating the correction factor for hyperglycemia · Am J Med (1999)

For educational purposes only. Not for clinical decision-making without professional oversight.