In hyperglycemia there may be apparent hyponatremia that may not reflect actual total body sodium status. Apparent mild hyponatremia occurring with very high glucose levels may actually represent hypernatremia.
Patient selection: blood glucose over 200 mg/dL
Equation of Katz:
corrected sodium level in mmol/L =
= (measured sodium in mmol/L) + ((variable) * ((glucose in mmol/L) -5.5) / 5.5)
The variable is a value from 1.3 to 2.0, most often 1.6. This corresponds to the 1.6 mmol/L change in serum sodium for every 100 mg/dL of glucose.
According to Moran and Jamison the choice of the variable is affected by volume status:
Volume Status
Variable
euvolemia
1.6
volume depletion
2.0
volume expansion
1.2
This can be rewritten as:
corrected sodium level in mmol/L =
= (measured sodium in mmol/L) + (0.016 * ((measured glucose in mg/dL) – 100))
where:
• 0.016 is the variable 1.6 divided by 100.
Another equation for correcting the serum sodium is:
corrected sodium level in mEq/L = corrected sodium level in mmol/L =
= (measured sodium in mEq/L) + ((variable) * (glucose in mg/dL) /100)
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