Paucis Verbis: Approach to increased osmolal gap

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 [1]
Go to ALiEM Cards for more resources.

Reference

1. 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]

Author information

Michelle Lin, MD

ALiEM Founder and CEO
Professor and Digital Innovation Lab Director
Department of Emergency Medicine
University of California, San Francisco

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