Osmolar Gap
Difference between measured and calculated osmolality — a screen for unmeasured osmotically active substances such as toxic alcohols.
Formula
Osmolar gap = Measured osmolality − (2 × Na + Glucose/18 + BUN/2.8)
Result
Enter all values to see the result.
Limitations
- A normal osmolar gap does not exclude toxic alcohol ingestion, particularly later in the course once the parent alcohol has already been metabolized.
- Requires a directly measured serum osmolality (by freezing-point depression) — this calculator cannot substitute for that measurement.
- Elevated but nonspecific — it flags the possibility of an unmeasured osmole without identifying which one; clinical context and specific levels are required to confirm the cause.
References
- Standard calculated-osmolality formula (2×Na + glucose/18 + BUN/2.8); see also Osmolar Gap in the Physiology Library.
Clinical Context & Relevant Topics (4)
Disease ReferenceStepwise 6-step interpretation algorithm, compensation formulas, albumin-corrected anion gap, delta ratio, and Stewart physicochemical (SID) principles.
Differential diagnosis (GOLD MARK vs HARDCARP), toxic alcohol osmolar gaps, Urine Anion Gap, and current sodium bicarbonate evidence including BICAR-ICU and BICARICU-2.
Resuscitate first, identify toxidromes and ECG/acid-base threats, use toxin-specific antidotes, and escalate early to poison-center, extracorporeal, or ECLS support when physiology demands it.
ARAS neuroanatomy, structural vs toxic-metabolic coma, the comprehensive Coma Exam (pupils, cold calorics, posturing), FOUR score, and CAM-ICU delirium.
Relevant Clinical Pathways (8)
Decision ProtocolsFrom urgent 'AEIOU' indication screening and modality selection to vascular access, dosing, and anticoagulation.
From primary disorder confirmation and Anion Gap calculation to Winter's compensation, delta ratio, and targeted source control.