Correct serum sodium for hyperglycaemia: Hillier formula with 2.4 factor per 5.6 mmol/L glucose above normal.
In hyperglycaemia, osmotic water shift from cells to plasma lowers measured sodium by 1.6–2.4 mmol/L per 5.6 mmol/L glucose above 5.6. The 1999 Hillier formula uses a 2.4 factor (more accurate than the older Katz 1.6). Pseudo-hyponatraemia versus true hyponatraemia requires different management: in DKA the priority is glucose correction.
Hillier TA, Abbott RD, Barrett EJ. Am J Med 1999;106(4):399-403
Formula version: hillier-1999-v1