We often talk about calculating the anion gap in the evaluation of patients. What about the osmolal gap? When do you calculate this? What’s the differential diagnosis for an increased gap?
I recently came upon a nice 2011 review in the American Journal of Kidney Disease called “Approach to the evaluation of a patient with an increased serum osmolal gap and high-anion-gap metabolic acidosis”. It’s always nice to revisit and review this concept. You’ll always learn something new. For instance, I didn’t know that salicylates cause anion gaps as well as osmolal gaps.
So don’t forget to calculate an osmolal gap for patients with an unexplained metabolic acidosis anion gap.
PV Card: Approach to Osmolal Gap
Adapted from  Go to ALiEM Cards for more resources.
- Kraut J, Xing S. Approach to the evaluation of a patient with an increased serum osmolal gap and high-anion-gap metabolic acidosis. Am J Kidney Dis. 2011;58(3):480-484. [PubMed]