A calculator for serum sodium correction in the setting of hyperglycemia. In normal physiology, effective osmolarity in the presence of overt hyperglycemia is more clinically relevant than the estimate of serum sodium concentration.
Formula
Corrected serum sodium (Hillier formula) = Measured sodium in mEq/L + 0.024 x (serum glucose in mg/dL – 100)
Application (Corrected Sodium for serum glucose levels)
For patients with severe hyperglycemia, it is worth noting that the tonicity of extracellular fluid rises above that of intracellular fluid. This results in a temporary transcellular shift of glucose and water, in opposite directions (water moves into the extracellular space whilst glucose moves into the intracellular space). Dilution of serum sodium in the extracellular fluid leads to transient lowering of serum sodium.
Limitations
Traditionally, two competing papers are cited in the literature when it comes to the right approach for sodium correction in hyperglycemia. The original estimate by Katz in 1973 used a sodium correction factor of 1.6mEq/L for every 100mg/dL increase in serum glucose. An external validation study by Hillier et al in 1999 recalibrated the equation using a sodium correction factor of 2.4mEq/L for every 100mg/dL increase in serum glucose.
References
- Katz MA. Hyperglycemia-induced hyponatremia–calculation of expected serum sodium depression. N Engl J Med. 1973 Oct 18;289(16):843-4. doi: 10.1056/NEJM197310182891607. PMID: 4763428.
- Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. Am J Med. 1999 Apr;106(4):399-403. doi: 10.1016/s0002-9343(99)00055-8. PMID: 10225241.
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