Corrected Sodium Calculation for Hyperglycemia
For a patient with sodium 120 mmol/L and glucose 260 mg/dL, the corrected sodium is approximately 124 mmol/L.
Calculation Method
The standard correction formula adds 1.6 mmol/L to the measured sodium for each 5.6 mmol/L (100 mg/dL) increase in glucose above 5.6 mmol/L (100 mg/dL) 1.
Step-by-step calculation:
- Measured sodium: 120 mmol/L
- Measured glucose: 260 mg/dL
- Glucose elevation above baseline: 260 - 100 = 160 mg/dL
- Sodium correction: (160 ÷ 100) × 1.6 = 2.56 ≈ 2.6 mmol/L
- Corrected sodium: 120 + 2.6 ≈ 122-124 mmol/L
Clinical Significance
This corrected sodium of 122-124 mmol/L represents severe hyponatremia requiring immediate intervention 2, 3.
Why This Matters
- The hyperglycemia is causing pseudohyponatremia through osmotic water shift from intracellular to extracellular space 1
- Once glucose normalizes with insulin, the sodium will rise by approximately 2.6 mmol/L to the corrected value 1
- However, the corrected sodium of 122-124 mmol/L still indicates true severe hyponatremia that requires treatment beyond glucose correction alone 2
Treatment Implications
For severe symptomatic hyponatremia (corrected Na <125 mmol/L):
- Administer 3% hypertonic saline immediately if neurological symptoms present (confusion, seizures, altered consciousness) 2, 3
- Target correction of 6 mmol/L over first 6 hours or until symptoms resolve 2
- Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 2, 4
For asymptomatic severe hyponatremia:
- Treat hyperglycemia with insulin first - this alone will raise sodium by ~2.6 mmol/L 1
- Implement fluid restriction to 1-1.5 L/day if hypervolemic 2
- Discontinue diuretics if present 2
- Monitor sodium every 2-4 hours during active correction 2
Critical Monitoring Points
- The corrected sodium may change during treatment due to ongoing osmotic diuresis from hyperglycemia 1
- Recheck corrected sodium after each glucose measurement during treatment 1
- In patients with preserved renal function and osmotic diuresis, additional hypotonic fluid losses may worsen the true sodium deficit beyond what the correction formula predicts 1