Corrected Sodium Formula in Hyperglycemia
The corrected sodium formula is: Corrected [Na⁺] = Measured [Na⁺] + 1.6 × ([Glucose in mg/dL - 100]/100), which should be calculated for every hyperglycemic patient to guide fluid therapy decisions. 1, 2
The Formula and Its Application
The standard correction factor adds 1.6 mEq/L to the measured sodium for every 100 mg/dL of glucose above 100 mg/dL 1, 2. This can be simplified as adding 1.6 mmol/L per 5.6 mmol/L (100 mg/dL) decrease in glucose 3.
Example calculation: If measured sodium is 135 mEq/L and glucose is 900 mg/dL:
- Corrected Na⁺ = 135 + 1.6 × [(900-100)/100]
- Corrected Na⁺ = 135 + 1.6 × 8 = 135 + 12.8 = 147.8 mEq/L 1, 2
Critical Clinical Applications
Fluid Selection in DKA/HHS
The corrected sodium—not the measured sodium—determines which IV fluid to use after initial resuscitation: 1, 2
- If corrected sodium is LOW: Continue 0.9% NaCl at 4-14 ml/kg/h 1, 2
- If corrected sodium is NORMAL or ELEVATED: Switch to 0.45% NaCl at 4-14 ml/kg/h 1, 2
This distinction is critical because using measured sodium alone will lead to inappropriate fluid selection and potentially worsen hypernatremia 2.
Why This Matters for Outcomes
Hyperglycemia causes a dilutional hyponatremia by drawing water from intracellular to extracellular spaces 3. The measured sodium underestimates the true sodium status. When glucose normalizes with insulin, water shifts back intracellularly, and the "true" sodium level emerges 3.
In HHS, the mean corrected sodium is 160.8 mEq/L (severe hypernatremia range), despite measured sodium often appearing normal 3. Failing to recognize this leads to cerebral edema risk if hypotonic fluids aren't used appropriately.
Separate Calculation: Effective Osmolality
Important distinction: Use MEASURED sodium (not corrected) to calculate effective serum osmolality: 1, 2
- Effective osmolality = 2[measured Na⁺ (mEq/L)] + glucose (mg/dL)/18 1, 2
- This assesses severity and monitors treatment progress 2
- Goal: Decrease osmolality by no more than 3 mOsm/kg/h to prevent cerebral edema 1, 2
Common Pitfalls to Avoid
Never use measured sodium alone to guide fluid choice—this is the most common error and can result in worsening hypernatremia or inadequate correction 2. The corrected sodium reveals the degree of hypertonicity caused by osmotic diuresis losses 3.
Monitor corrected sodium during treatment, not just at presentation 3. The corrected sodium can change during therapy due to ongoing fluid losses, so recalculate it with each sodium check 3.
Do not exceed 3 mOsm/kg/h reduction in osmolality—this carries significant mortality risk from cerebral edema 1, 2. Check electrolytes every 2-4 hours initially to ensure safe correction rates 2.
Clinical Context
In DKA, mean corrected sodium is typically 141.1 mEq/L (eunatremic range) across large case series, but individual patients may have corrected sodium in the hypernatremic range with adverse neurological consequences if not recognized 3. In HHS, corrected sodium averages 160.8 mEq/L, indicating severe water deficit requiring aggressive hypotonic fluid replacement 3.
Patients with stage 5 CKD and hyperglycemia have minimal osmotic diuresis, so their corrected sodium (mean 139.0 mEq/L) more closely reflects measured values 3. In contrast, patients with preserved renal function and DKA/HHS have substantial osmotic diuresis, creating larger discrepancies between measured and corrected sodium 3.