serum osmolal gap

Reference interval

• < 10 mOsm/L

Principle

• calculated serum osmolality is given by the formula:

2[Na+] + glucose (mg/dL)/18 + BUN (mg/dL)/2.8

+ BAL* (mg/dL)/3.7) to exclude ethanol; ethanol (mg/dL)/4.6 (MKSAP20)

* BAL = blood alcohol level

• the osmolal gap is the difference between the measured vs calculated osmolality
• it is important to obtain [Na+], [glucose] & [[[A32085|BUN]]] on the same specimen as the measured osmolality measured vs the calculated osmolality

Clinical significance

• an increased osmolal gap may indicate a toxin
• a normal osmolal gap does not rule out all toxins

Increases

• ethanol
• ethylene glycol
• isopropanol
• methanol
• propylene glycol
• glycerol
• mannitol
• sorbitol
• acetone
• diatrizoate

More general terms

• general chemistry test

Additional terms

• serum osmolality
• urine osmolal gap