Osmolar gap
Calculated osmolarity = 2(Na+) + urea + glucose = 275-295 mosm/l
Osmolar gap = measured - calculated osmolarity. Normal ≤10
Causes of an increased osmolar gap are:
- Lab error
- Decreased serum water content
- Hyperlipidaemia
- Hyperproteinaemia
- Additional LMW substances in the serum:
- ethanol
- methanol
- isopropyl alcohol
- ethylene glycol
- mannitol
