Corrected Sodium Calculator

The Corrected Sodium Calculator is an essential clinical tool for healthcare providers managing patients with hyperglycemia. It adjusts measured serum sodium levels to account for the dilutional effect caused by elevated blood glucose, revealing the patient's true sodium status. This is particularly critical in diabetic emergencies like diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS).

Understanding Corrected Sodium

When blood glucose rises significantly above normal levels, it creates an osmotic gradient that pulls water from inside cells into the bloodstream. This water influx dilutes the sodium concentration, causing what appears to be hyponatremia (low sodium) on lab results. However, this is dilutional hyponatremia or pseudohyponatremia — the total body sodium may be normal or even elevated, but the measured concentration is artificially lowered by the extra water.

Corrected Sodium Formulas

Two main formulas are used to calculate corrected sodium:

Katz Formula (Traditional)

The Katz formula, published in 1973, is the most widely used correction factor. It adds 1.6 mEq/L to the measured sodium for every 100 mg/dL that glucose exceeds 100 mg/dL.

Hillier Formula (Alternative)

The Hillier formula, based on research from 1999, uses a higher correction factor of 2.4 mEq/L. Studies suggest this may be more accurate, particularly when glucose levels exceed 400 mg/dL.

Which Formula Should I Use?

Clinical Interpretation

Understanding the corrected sodium value helps guide treatment decisions:

When to Calculate Corrected Sodium

Calculate corrected sodium in these clinical scenarios:

• Diabetic Ketoacidosis (DKA) — Essential for fluid management decisions
• Hyperosmolar Hyperglycemic State (HHS) — Critical for determining true hydration status
• New diabetes diagnosis — When presenting with severe hyperglycemia
• Any hyponatremia with concurrent hyperglycemia — To differentiate true vs. dilutional hyponatremia
• Critical care patients — When glucose and sodium are both abnormal

Clinical Implications

If Corrected Sodium is Normal (135-145 mEq/L)

The apparent hyponatremia is purely dilutional. As glucose normalizes with treatment, sodium will rise proportionally. Standard DKA/HHS fluid protocols are appropriate.

If Corrected Sodium is Still Low (< 135 mEq/L)

True hyponatremia exists beyond the dilutional effect. Be cautious with aggressive fluid resuscitation. Consider underlying causes (SIADH, adrenal insufficiency, renal losses).

If Corrected Sodium is Elevated (> 145 mEq/L)

Significant free water deficit exists. The patient is more dehydrated than the measured sodium suggests. More aggressive hypotonic fluid replacement may be needed.

Practical Example

Consider a patient with DKA presenting with:

• Measured sodium: 128 mEq/L (appears low)
• Blood glucose: 650 mg/dL (severely elevated)

Using the Katz formula:

The corrected sodium of 136.8 mEq/L is within normal range, indicating the low measured sodium is due to dilution from hyperglycemia. As glucose normalizes, sodium will rise accordingly.

Important Considerations

• Recheck sodium as glucose normalizes — Sodium should rise proportionally as glucose falls; if it doesn't, investigate other causes
• Avoid overcorrection — Rapid sodium changes can cause osmotic demyelination syndrome (ODS)
• Consider the clinical picture — Formulas are estimates; integrate with physical exam and other labs
• Monitor trends — Serial measurements are more valuable than single values

Frequently Asked Questions

What is corrected sodium and why is it important?

Corrected sodium is an adjusted serum sodium value that accounts for the dilutional effect of hyperglycemia. When blood glucose is elevated, water shifts from inside cells to the bloodstream, diluting sodium and causing artificially low readings. The corrected sodium reveals the patient's true sodium status, which is critical for proper management of diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS).

What is the formula for corrected sodium?

The most widely used formula is the Katz formula: Corrected Na = Measured Na + 1.6 × [(Glucose - 100) / 100]. This adds 1.6 mEq/L to the measured sodium for every 100 mg/dL of glucose above 100 mg/dL. An alternative is the Hillier formula which uses a correction factor of 2.4 mEq/L per 100 mg/dL, which may be more accurate for severe hyperglycemia.

Should I use the Katz or Hillier formula?

The Katz formula (1.6 mEq/L correction) is the traditional standard used in most clinical settings. The Hillier formula (2.4 mEq/L correction) was developed based on research suggesting the traditional factor underestimates the correction needed, particularly when glucose exceeds 400 mg/dL. Many clinicians use the Katz formula for routine cases and consider the Hillier formula for severe hyperglycemia.

What is the normal range for corrected sodium?

The normal range for sodium (including corrected sodium) is 135-145 mEq/L. Values below 135 indicate hyponatremia, while values above 145 indicate hypernatremia. Severe abnormalities (below 120 or above 155 mEq/L) require urgent attention due to risk of neurological complications.

How does hyperglycemia cause pseudohyponatremia?

Hyperglycemia causes pseudohyponatremia through an osmotic effect. High blood glucose creates an osmotic gradient that draws water from intracellular spaces into the bloodstream. This water influx dilutes the sodium concentration, making it appear lower than the patient's actual sodium status. This is called dilutional or translocational hyponatremia, and the corrected sodium formula reverses this effect mathematically.

When should I calculate corrected sodium?

Calculate corrected sodium whenever a patient has hyperglycemia (glucose > 100 mg/dL) along with a sodium measurement. It is especially important in diabetic emergencies like DKA and HHS, new diabetes diagnosis with severe hyperglycemia, and any critically ill patient with concurrent hyperglycemia and apparent hyponatremia.

References

• Katz MA. Hyperglycemia-induced hyponatremia. N Engl J Med. 1973
• Hillier TA et al. Hyponatremia: evaluating the correction factor. Am J Med. 1999
• Hyponatremia — Wikipedia