1Sodium Correction — Clinical Guide
Hillier: Corrected Na = Measured Na + 2.4 × (Glucose − 100) ÷ 100
(Glucose in mg/dL. For mmol/L: convert × 18 first)
Why Correct Sodium for Glucose?
Hyperglycaemia creates an osmotic gradient that draws water from the intracellular to extracellular space, diluting serum sodium by approximately 1.6–2.4 mmol/L for every 100 mg/dL (5.6 mmol/L) rise in glucose above 100 mg/dL. The measured sodium is therefore artifactually low. The corrected sodium reflects what the sodium would be at a normal glucose level — this is the clinically important value for managing fluid replacement.
Clinical Implications in DKA and HHS
- DKA: Corrected Na helps assess true hydration status. In DKA, corrected Na >135 indicates hypernatraemia that will be unmasked as glucose falls with treatment — use more hypotonic fluid (0.45% NaCl after initial resuscitation)
- HHS: Corrected Na often markedly elevated in HHS (corrected Na >145 is common). Guides initial fluid choice — normal saline first to restore volume, then switch to 0.45% NaCl to correct free water deficit
- Hillier formula (2.4): Preferred for glucose >400 mg/dL — more accurate at very high glucose levels. Katz (1.6) traditionally taught but underestimates correction at extreme hyperglycaemia
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.
2Frequently asked questions
What is the corrected sodium formula in hyperglycaemia?
Hyperglycaemia causes osmotic shift of water from cells into plasma, diluting sodium. Corrected Na = Measured Na + 2.4 × [(Glucose − 100) / 100] (glucose in mg/dL). Alternative (more accurate for severe hyperglycaemia): Corrected Na = Measured Na + 1.6 × [(Glucose − 100) / 100]. If corrected Na is high (>145 mEq/L) despite apparent hyponatraemia, the patient is actually hypernatraemic — true sodium deficit is masked by glucose dilution.
What is the correction rate for hyponatraemia?
Chronic hyponatraemia (>48 hours or unknown duration): correct sodium at maximum 10–12 mEq/L per 24 hours (or 8 mEq/L/24h if high risk of osmotic demyelination — alcoholism, malnutrition, hypokalaemia, liver disease). Correction faster than this risks osmotic demyelination syndrome (ODS) — a potentially fatal pontine and extrapontine demyelination causing paraplegia, dysarthria, and locked-in syndrome.
What is osmotic demyelination syndrome?
ODS (formerly central pontine myelinolysis) occurs when chronic hyponatraemia is corrected too rapidly. Brain cells that have adapted to low sodium by losing osmolytes are suddenly exposed to rapid osmolality change, causing myelin sheath destruction. Onset 2–6 days after overcorrection. Symptoms: pseudobulbar palsy, spastic quadriplegia, dysarthria, dysphagia, altered consciousness. Prevention: strict rate limit of ≤10–12 mEq/L/24h, and re-lowering sodium with dextrose water + desmopressin if overcorrection occurs.
How is acute symptomatic hyponatraemia treated?
Acute severe hyponatraemia (seizures, coma, severe symptoms): 3% hypertonic saline 100–150 mL IV over 20 minutes, repeat once or twice until symptoms resolve. Target: raise Na by 4–6 mEq/L rapidly to stop acute brain herniation, then switch to controlled correction (≤10 mEq/L/day). This is an emergency — do not apply chronic hyponatraemia correction limits in acute symptomatic cases.
What are the common causes of hyponatraemia in India?
Most common causes seen in Indian hospitals: SIADH (secondary to CNS infections — TB meningitis and bacterial meningitis are major causes in India, also pneumonia, post-neurosurgery), excessive hypotonic IV fluids (iatrogenic — especially in postoperative patients given large volumes of 5% dextrose), hypothyroidism, adrenal insufficiency (Addison's disease, post-steroid withdrawal), decompensated liver cirrhosis, and nephrotic syndrome.
How is hypernatraemia managed?
Hypernatraemia (Na >145 mEq/L): identify and treat cause (inadequate water intake, diabetes insipidus, excessive sodium load). Free water deficit = 0.6 × weight × [(Na/140) − 1]. Replace deficit with oral water (preferred) or IV 5% dextrose or 0.45% saline. Correction rate: no faster than 10–12 mEq/L/day for chronic hypernatraemia (risk of cerebral oedema with rapid correction). Monitor Na every 4–6 hours during active correction.
Medical disclaimer: This calculator is for educational and clinical decision-support purposes only. It does not replace clinical judgment or specialist consultation. RxMedCalc is not liable for clinical decisions made solely on this tool.