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Hyperglycemia induces osmotic water shifts from intracellular to extracellular compartments, diluting serum sodium and producing pseudohyponatremia. A measured Na⁺ value in isolation is misleading when serum glucose exceeds 100 mg/dL. Failure to correct sodium for elevated glucose can mask true hypernatremia or exaggerate apparent hyponatremia, leading to inappropriate fluid management - particularly dangerous in diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS). This calculator applies both the Katz (1973) correction factor of 1.6 mEq/L per 100 mg/dL glucose elevation and the Hillier (1999) revised factor of 2.4 mEq/L, which better approximates the dilutional effect at glucose concentrations above 400 mg/dL.

Note: both correction formulas assume a linear relationship between glucose elevation and sodium dilution, which is an approximation. The Katz factor tends to underestimate correction at extreme glucose levels (> 400 mg/dL). Neither formula accounts for other osmotically active solutes such as mannitol or contrast agents. Always interpret corrected sodium within full clinical context including serum osmolality, volume status, and renal function.

Formulas

The Katz (1973) correction applies a linear adjustment of 1.6 mEq/L for every 100 mg/dL glucose above the normal baseline of 100 mg/dL:

Na_corrected = Na_measured + 1.6 × Glucose − 100100

The Hillier (1999) revision uses a factor of 2.4 instead, which better models the nonlinear osmotic shift at extreme hyperglycemia:

Na_corrected = Na_measured + 2.4 × Glucose − 100100

Where Na_measured is the lab-reported serum sodium in mEq/L, and Glucose is the serum glucose in mg/dL. If glucose is provided in mmol/L, convert first:

Glucose_mg/dL = Glucose_mmol/L × 18.0182

When Glucose ≤ 100 mg/dL, no correction is applied and Na_corrected = Na_measured.

Reference Data

Parameter	Normal Range	Unit	Clinical Note
Serum Sodium (Na⁺)	135 - 145	mEq/L	Primary extracellular cation
Fasting Glucose	70 - 100	mg/dL	Reference baseline for correction
Fasting Glucose	3.9 - 5.6	mmol/L	SI unit equivalent
Hyponatremia (Mild)	130 - 134	mEq/L	Often asymptomatic
Hyponatremia (Moderate)	125 - 129	mEq/L	Nausea, confusion possible
Hyponatremia (Severe)	< 125	mEq/L	Seizures, coma risk
Hypernatremia (Mild)	146 - 150	mEq/L	Thirst, irritability
Hypernatremia (Severe)	> 160	mEq/L	Altered mental status, mortality risk
DKA Glucose Range	> 250	mg/dL	Diabetic ketoacidosis threshold
HHS Glucose Range	> 600	mg/dL	Hyperosmolar hyperglycemic state
Katz Correction Factor	1.6	mEq/L per 100 mg/dL	Classic 1973 derivation
Hillier Correction Factor	2.4	mEq/L per 100 mg/dL	Revised 1999 factor for glucose > 400
Glucose Conversion	1 mmol/L = 18.0182 mg/dL	-	Molecular weight of glucose: 180.16 g/mol
Serum Osmolality (Normal)	275 - 295	mOsm/kg	Context for sodium interpretation
Osmolar Gap (Normal)	< 10	mOsm/kg	Elevated suggests unmeasured osmoles
Tonicity (Effective Osmolality)	275 - 295	mOsm/kg	Excludes urea contribution

Frequently Asked Questions

The Hillier correction factor of 2.4 mEq/L per 100 mg/dL was derived from regression analysis of patients with glucose levels exceeding 400 mg/dL. At these extreme concentrations, the Katz factor of 1.6 systematically underestimates the dilutional effect. For glucose values between 100 - 400 mg/dL, both formulas produce clinically similar results. For glucose above 400 mg/dL (common in HHS), the Hillier factor is recommended by multiple endocrinology references.

The original Katz derivation used 100 mg/dL (5.6 mmol/L) as the normoglycemic reference point in the correction equation. This is an arbitrary convention, not a physiological constant. Some authors have proposed using 140 mg/dL as a more realistic postprandial baseline. However, 100 remains the standard in published correction formulas and clinical decision support tools. Using a different baseline changes the magnitude of correction.

No. If serum glucose is at or below the 100 mg/dL baseline, the correction term is zero or negative. A negative correction would imply that sodium should be adjusted downward, which contradicts the purpose of the formula (detecting masked hypernatremia). This calculator clamps the correction at zero when glucose is below baseline, returning the measured sodium unchanged.

The correction formulas assume glucose is the sole effective osmole causing water redistribution. Mannitol, sorbitol, glycine (post-TURP), and radiocontrast agents also create osmotic gradients that dilute sodium independently. In these cases, the corrected sodium from glucose alone will still underestimate the true sodium concentration. Calculate serum osmolality and osmolar gap to identify unmeasured osmoles.

The molecular weight of glucose is 180.16 g/mol, giving a conversion factor of 18.0182 (rounding 1000 ÷ 180.16 ÷ 10). Some references round this to 18, introducing up to 0.1% error. At a glucose of 50 mmol/L, the difference between using 18 and 18.0182 is approximately 0.9 mg/dL, which is clinically negligible.

If the corrected sodium exceeds 145 mEq/L while the measured sodium appears normal or low, the patient has dilutional hyponatremia masking true hypernatremia. This is clinically significant in DKA management: as glucose normalizes with insulin, water will redistribute intracellularly, and serum sodium will rise. Anticipate this rise to avoid overly aggressive hypotonic fluid administration.