Corrected Sodium Calculation for Hyperglycemia
For a measured sodium of 133 mmol/L with a blood glucose of 36.2 mmol/L (652 mg/dL), the corrected sodium is approximately 150 mmol/L, indicating severe hypernatremia that requires urgent treatment with hypotonic fluids.
The Correction Formula
The standard correction adds 1.6 mEq/L to the measured sodium for every 100 mg/dL (5.6 mmol/L) of glucose above 100 mg/dL (5.6 mmol/L) 1, 2. However, this relationship becomes nonlinear at extreme hyperglycemia.
Step-by-Step Calculation
For glucose >400 mg/dL (22.2 mmol/L), use a correction factor of 4.0 mEq/L per 100 mg/dL instead of 1.6 3. Your patient's glucose of 652 mg/dL falls into this category.
- Glucose elevation above baseline: 652 - 100 = 552 mg/dL
- Correction: (552 ÷ 100) × 4.0 = 22.1 mEq/L
- Corrected sodium: 133 + 22 = 155 mmol/L
Using the standard 1.6 factor would underestimate the true sodium status:
- Standard correction: (552 ÷ 100) × 1.6 = 8.8 mEq/L
- This would give 141.8 mmol/L, missing severe hypernatremia 3
Clinical Significance
The corrected sodium of 155 mmol/L indicates severe hypernatremia from osmotic diuresis, not true hyponatremia 1, 2. The measured hyponatremia (133 mmol/L) is pseudohyponatremia caused by osmotic water shift from intracellular to extracellular space 1.
Why This Matters for Treatment
Patients with corrected hypernatremia (>150 mmol/L) have significantly higher 90-day mortality (adjusted HR 2.68) compared to those with normal corrected sodium 4. In hyperosmolar hyperglycemic state (HHS), mean corrected sodium reaches 160.8 mmol/L, indicating severe free water deficit from osmotic diuresis 2.
Treatment Implications
Use 0.45% NaCl (hypotonic saline) at 4-14 mL/kg/h when corrected sodium is elevated 1. This patient requires hypotonic fluid replacement to address the water deficit from osmotic diuresis, not sodium replacement 1, 2.
Fluid Selection Algorithm
- Corrected Na >145 mmol/L: Use 0.45% NaCl 1
- Corrected Na 135-145 mmol/L: Use 0.9% NaCl 1
- Corrected Na <135 mmol/L: Use 0.9% NaCl 1
Critical Monitoring Parameters
Recalculate corrected sodium every 2-4 hours as glucose normalizes 1, 2. The corrected sodium changes during treatment due to ongoing osmotic diuresis and should guide ongoing fluid selection 2.
Limit the rate of serum osmolality decrease to ≤3 mOsm/kg/h to prevent cerebral edema 1. Overly rapid correction causes osmotic demyelination syndrome, particularly dangerous in this setting 1.
Monitor for neurological deterioration during correction 2. Several reports document adverse neurological consequences when corrected sodium rises excessively during DKA/HHS treatment 2.
Common Pitfalls to Avoid
Using measured sodium (133 mmol/L) instead of corrected sodium (155 mmol/L) leads to inappropriate isotonic or hypertonic saline administration, worsening hypernatremia and increasing mortality risk 1, 4. Measured hyponatremia in severe hyperglycemia does not predict mortality, but corrected hypernatremia strongly predicts poor outcomes 4.
Failing to use the higher correction factor (4.0) for glucose >400 mg/dL underestimates true sodium status by approximately 13 mEq/L at this glucose level 3. The standard 1.6 factor only applies accurately up to glucose 400 mg/dL 3.
Not reassessing corrected sodium as glucose normalizes results in continued inappropriate fluid selection 1, 2. As glucose falls with insulin therapy, the osmotic gradient reverses and corrected sodium must be recalculated 2.