Osmolar Gap

Note: normal serum osmolarity is 280 to 300.

Osmolar gap = calculated osmolarity - actual osmolarity

Calc osm=
2Na + glucose/18 + BUN/2.8

Can round off:
2Na +glucose/20 +BUN/3

Increased in:

If the hx does not suggest either lactic acidosis or ketoacidosis, then a high osmolal gap, esp if > 25 suggest methanol or ethylene glycol intox.