What the sodium would be at a normal glucose level (Katz 1973).

What it is and when to use it

Corrected sodium for hyperglycemia estimates what the patient's serum sodium would be once glucose is normalized. Hyperglycemia drives an osmotic shift of water from the intracellular space into plasma, diluting the measured sodium; this is a true translocational (hypertonic) hyponatremia, not a pseudohyponatremia (which is a laboratory artifact from hyperlipidemia or hyperproteinemia with normal osmolality). It is typically applied in diabetic ketoacidosis, hyperosmolar hyperglycemic state, and any marked hyperglycemia. The most widely used correction adds 1.6 mEq/L of sodium for every 100 mg/dL of glucose above 100 mg/dL; the alternative factor of 2.4 mEq/L (Hillier, 1999) is considered more accurate at very high glucose levels. It is a standard physiological calculation rather than a society-endorsed score, but its use is incorporated into protocols for managing hyperglycemic crises (ADA).

How to interpret it

The result is the sodium concentration expected if glucose were normal. If the corrected sodium is normal (135-145 mEq/L) or elevated despite a low measured value, the hyponatremia is attributable to the osmotic shift from hyperglycemia and is expected to resolve as glucose is corrected, with no specific hyponatremia treatment needed. A corrected sodium below 135 mEq/L indicates a concurrent true hyponatremia that should be evaluated and treated on its own. An elevated corrected sodium (>145 mEq/L) flags a significant free-water deficit. Initial resuscitation of the hyperglycemic crisis uses isotonic saline (0.9%); switching to hypotonic saline (0.45%) is reserved for later phases once the patient is euvolemic and the corrected sodium is normal or high. The trend in corrected sodium during treatment is clinically more meaningful than any single isolated value.

Limitations and when not to use it

The formula assumes reasonably stable renal function and volume status and has been validated mainly in acute hyperglycemia; the correction factors (1.6 vs 2.4) derive from small studies and may under- or overestimate depending on the degree of hyperglycemia. It does not apply to pseudohyponatremia from hyperlipidemia or hyperproteinemia (a different laboratory artifact) and does not replace direct measurement of sodium once glucose is normalized. It does not assess overall plasma osmolality, acid-base status, or total water deficit, and should not by itself guide the rate of sodium correction, where the risk of osmotic demyelination syndrome (central pontine myelinolysis) from overly rapid correction must be monitored.

Frequently asked questions

What formula is used to correct sodium for hyperglycemia?

Corrected sodium = measured sodium + 1.6 × [(glucose in mg/dL − 100) / 100]. Many authors prefer the 2.4 factor (Hillier) when glucose exceeds 400 mg/dL because it fits real-world data more closely.

Why does sodium fall when glucose is high?

Glucose is osmotically active and pulls water out of cells into the plasma, diluting sodium. This is a true dilutional (translocational, hypertonic) hyponatremia, not a real sodium loss nor a laboratory artifact, and it usually corrects once glucose is normalized.

Does corrected sodium replace the measured value for guiding treatment?

No. Corrected sodium guides fluid therapy and helps distinguish hyperglycemia-driven hyponatremia from a concurrent true hyponatremia, but it should always be confirmed with serial direct sodium measurements as glucose is corrected.