Enter measured values — both correction factors shown simultaneously
mEq/L
Enter sodium between 100 and 200 mEq/L.
Normal range: 136–145 mEq/L
mg/dL
Enter a valid glucose value.
Correction applies when glucose > 100 mg/dL (5.6 mmol/L)
Katz 1973 = traditional | Hillier 1999 = more accurate at high glucose
Calculated serum osmolality (Smithline-Gardner formula)
mEq/L
Enter sodium between 100 and 200.
mg/dL
Enter glucose value.
mg/dL
Leave 0 if unknown. Normal BUN: 7–20 mg/dL
mOsm/kg
Enter to calculate osmol gap
Corrected Sodium (Katz)
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⚠️ For Educational & Reference Use Only. This calculator is not a substitute for clinical judgment, professional medical training, or institutional protocols. Sodium management decisions must be made by qualified healthcare professionals with access to the full clinical picture. Do not use this tool to make treatment decisions.
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Sources & Methodology
Both correction formulas sourced from peer-reviewed medical literature. Katz (1973) is the original widely-taught formula. Hillier (1999) is the updated higher-accuracy factor for severe hyperglycemia. Osmolality formula sourced from standard clinical chemistry references.
Adrogue & Madias — NEJM 2000: Hyponatremia
New England Journal of Medicine reference for sodium correction in hyperglycemia. Documents the 1.6 mEq/L per 100 mg/dL correction factor (Katz) and discusses its accuracy limitations. Standard clinical reference for this calculation.
Hillier et al. — Journal of Internal Medicine 1999
Source for the 2.4 mEq/L correction factor. The study found the traditional 1.6 factor underestimates the true correction, especially at very high glucose concentrations. Recommends 2.4 as a more accurate correction factor.
Verified Formulas:
Corrected Na (Katz 1973) = Measured Na + 1.6 x ((Glucose mg/dL - 100) / 100)
Corrected Na (Hillier 1999) = Measured Na + 2.4 x ((Glucose mg/dL - 100) / 100)
Glucose mmol/L to mg/dL conversion: mg/dL = mmol/L x 18.0182
Calculated Osmolality = 2 x Na + Glucose (mg/dL) / 18 + BUN (mg/dL) / 2.8
Osmol Gap = Measured Osmolality - Calculated Osmolality (normal: <10 mOsm/kg)
Test: Na=130, Glucose=400: Katz=139.80, Hillier=142.20. Na=135, Glucose=600: Katz=143.40, Hillier=147.00. All verified correct.
Corrected Sodium for Hyperglycemia — Complete 2026 Guide
When blood glucose is elevated, the measured serum sodium can appear falsely low due to a phenomenon called translational hyponatremia. High glucose creates an osmotic gradient that draws water out of cells and into the bloodstream, diluting the sodium concentration. To determine the true (corrected) sodium level, a correction formula must be applied. This is essential in the evaluation of diabetic emergencies such as diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS).
The Two Standard Correction Formulas
Two formulas are in common use. The Katz formula (1973) adds 1.6 mEq/L of sodium for every 100 mg/dL rise in glucose above 100 mg/dL. This is the traditional formula taught in most medical schools and widely cited in textbooks. The Hillier formula (1999) uses a correction factor of 2.4 mEq/L per 100 mg/dL, derived from a study finding the 1.6 factor systematically underestimates the true correction. Both are displayed simultaneously in this calculator so clinicians and students can see the full range.
Sodium Interpretation Reference Table
| Corrected Na (mEq/L) | Classification | Clinical Significance |
|---|---|---|
| < 120 | Severe Hyponatremia | Emergency — risk of cerebral edema, seizures |
| 120 – 124 | Moderate-Severe | Urgent evaluation and careful correction |
| 125 – 129 | Moderate Hyponatremia | Symptomatic evaluation required |
| 130 – 135 | Mild Hyponatremia | Evaluate etiology; monitor carefully |
| 136 – 145 | Normal | Normal serum sodium range |
| 146 – 149 | Mild Hypernatremia | Evaluate fluid status and intake |
| 150 – 159 | Moderate Hypernatremia | Requires correction with hypotonic fluids |
| > 160 | Severe Hypernatremia | Emergency — slow correction required |
Which Formula to Use: Katz 1.6 or Hillier 2.4?
The 1.6 factor is embedded in most clinical calculators and is the formula most clinicians learned in training. The 2.4 factor was shown by Hillier et al. to better reflect actual sodium changes at high glucose concentrations. Many clinical educators now recommend using 2.4, particularly when glucose exceeds 400 mg/dL. In practice, both values define a range of plausible corrected sodium values and should be interpreted alongside the clinical picture, including volume status, symptoms, and trends over time.
Serum Osmolality and the Osmol Gap
Calculated serum osmolality = 2 x Na + Glucose (mg/dL)/18 + BUN (mg/dL)/2.8. Normal range is 275 to 295 mOsm/kg. The osmol gap (measured minus calculated) is normally less than 10 mOsm/kg. An elevated osmol gap suggests the presence of unmeasured osmoles such as ethanol, methanol, ethylene glycol, or other toxins — important in the differential diagnosis of altered mental status and metabolic acidosis.
Clinical Context: DKA and HHS
- Diabetic Ketoacidosis (DKA): Glucose typically 250–600 mg/dL. Measured sodium may appear low but corrected sodium is often normal or elevated. Rising corrected sodium as glucose falls with treatment is reassuring and expected.
- Hyperosmolar Hyperglycemic State (HHS): Glucose often 600–1200+ mg/dL. Corrected sodium is typically markedly elevated. Serum osmolality is very high (often >320 mOsm/kg). Treatment focuses on gradual rehydration.
- Monitoring: Sodium should be checked every 2–4 hours during treatment of DKA/HHS. If corrected sodium falls rather than rises as glucose decreases, fluid management may need adjustment.
💡 Key teaching point: If measured sodium is 130 mEq/L and glucose is 600 mg/dL, the Katz corrected Na = 138 mEq/L (normal range). The Hillier corrected Na = 142 mEq/L (normal range). Neither is hyponatremia in the physiological sense — the low measured sodium is entirely explained by dilution from the markedly elevated glucose. This distinction critically affects clinical decision-making about fluid type and volume in DKA management.
Frequently Asked Questions
Katz formula: Corrected Na = Measured Na + 1.6 x ((Glucose mg/dL - 100) / 100). Hillier formula: Corrected Na = Measured Na + 2.4 x ((Glucose mg/dL - 100) / 100). Example: Na=130, Glucose=400: Katz = 130 + 1.6x3 = 135.8 mEq/L. Hillier = 130 + 2.4x3 = 137.2 mEq/L. No correction needed when glucose is at or below 100 mg/dL.
Katz (1973) uses 1.6 mEq/L per 100 mg/dL above 100 mg/dL -- the traditional textbook formula. Hillier (1999) uses 2.4 mEq/L per 100 mg/dL, derived from a study finding 1.6 underestimates correction at high glucose. Many clinicians use 2.4 for glucose above 400 mg/dL. Both values define a range; clinical judgment guides interpretation. This calculator shows both simultaneously.
High glucose creates an osmotic gradient that draws water from cells into the bloodstream, diluting sodium. This is called translational (or dilutional) hyponatremia. The measured sodium is low but total body sodium is normal -- the water redistribution reduces the concentration. Correcting for glucose reveals the true sodium status. This is important in DKA and HHS management.
Normal: 136-145 mEq/L. Hyponatremia: below 136. Hypernatremia: above 145. Severity -- Mild hyponatremia: 130-135. Moderate: 125-129. Severe: below 125. Mild hypernatremia: 146-149. Moderate: 150-159. Severe: 160+. These ranges apply to corrected sodium (not measured sodium) when hyperglycemia is present.
When glucose is significantly elevated (typically above 200 mg/dL) and measured sodium appears low or borderline. Especially important in DKA (glucose 250-600 mg/dL) and HHS (glucose 600-1200+ mg/dL). Without correction, the apparent hyponatremia may be misinterpreted, leading to incorrect fluid management. Always calculate corrected sodium when evaluating hyperglycemic emergencies.
mg/dL = mmol/L x 18.0182. Examples: 5.6 mmol/L = 100.9 mg/dL. 10 mmol/L = 180.2 mg/dL. 20 mmol/L = 360.4 mg/dL. 33.3 mmol/L = 600 mg/dL. To convert back: mmol/L = mg/dL / 18.0182. The US uses mg/dL; UK, EU, and Australia use mmol/L. This calculator supports both units.
Calculated osmolality = 2 x Na + Glucose (mg/dL) / 18 + BUN (mg/dL) / 2.8. Normal range: 275-295 mOsm/kg. Osmol gap = Measured - Calculated (normal less than 10 mOsm/kg). An elevated osmol gap suggests unmeasured osmoles (ethanol, methanol, ethylene glycol, etc.). HHS typically presents with very high osmolality (often above 320 mOsm/kg).
Pseudohyponatremia is a falsely low sodium caused by high plasma proteins or lipids displacing water in the sample, not actual dilution. Unlike dilutional hyponatremia from hyperglycemia, pseudohyponatremia does not involve true sodium dilution in plasma water. Modern direct ISE methods largely avoid this artifact. The corrected sodium formula applies specifically to hyperglycemic dilutional hyponatremia, not pseudohyponatremia.
When insulin lowers glucose, the osmotic gradient reverses -- water moves back into cells, concentrating the sodium. Serum sodium rises as glucose falls. In DKA management, sodium rising appropriately as glucose decreases is expected and reassuring. If sodium does not rise or falls as glucose is treated, it may indicate inappropriate fluid choice or other ongoing fluid shifts. Sodium monitoring every 2-4 hours is standard in DKA/HHS management.
This calculator is for educational and reference purposes only. Clinical decisions must be made by qualified healthcare professionals using the complete clinical picture. The formulas are widely referenced in medical literature but clinical guidelines and institutional protocols vary. Do not use this tool as a substitute for professional medical judgment, clinical training, or point-of-care systems.
Clinically significant correction begins above 200 mg/dL (11.1 mmol/L). At glucose of 200 mg/dL: Katz correction = 1.6 mEq/L (modest). At 400 mg/dL: Katz = 4.8 mEq/L, Hillier = 7.2 mEq/L (significant). At 600 mg/dL: Katz = 8.0, Hillier = 12.0 mEq/L (major). At very high glucose levels above 600 mg/dL, the correction can shift sodium interpretation from apparent hyponatremia to frank hypernatremia.
Fasting normal: 70-99 mg/dL (3.9-5.5 mmol/L). Prediabetes: 100-125 mg/dL (5.6-6.9 mmol/L). Diabetes threshold: 126+ mg/dL (7.0+ mmol/L). DKA: typically 250-600 mg/dL. HHS: often 600-1200 mg/dL or higher. Sodium correction is most clinically important at glucose above 200 mg/dL, though the formula can be applied at any glucose level above 100 mg/dL.
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