Serum Osmolality Sodium (Na): mmol/L (optional) Potassium (K): mmol/L BUN: mg/dl Glucose: mg/dl Serum Osmolality = mOsm/kg Normal Range = 285 - 295 mOsm/kg Serum Osmolality = (2 x (Na + K)) + (BUN / 2.8) + (glucose / 18)