Value	Purpose	Formula	Normal value
Anion gap	Essential for evaluation of acid base disorders	Na– (Cl + HCO3)	7 to 13 mEq per L (7 to 13 mmol per L)
Osmolar gap	Difference between measured osmolality and calculated osmolality	Osmolality (measured) – osmolality (calculated)	< 10 mmol per L*
Serum osmolality	Measure of particles in a fluid compartment	2(Na + K) + (glucose/18) + (blood urea nitrogen/2.8)	285 to 295 mOsm per kg (285 to 295 mmol per kg) of water
Serum sodium correction	Hyperglycemia causes pseudohyponatremia	Na + 0.016(glucose – 100)	135 to 140 mEq per L (135 to 140 mmol per L)