Anion Gap
Narrows the differential for a metabolic acidosis by estimating the concentration of unmeasured anions in the plasma.
Formula
Anion gap = Na − (Cl + HCO3)
Result
Enter all values to see the result.
Limitations
- Should be corrected for albumin: a low albumin lowers the expected 'normal' gap by roughly 2.5 per 1 g/dL drop, and can mask a clinically significant gap acidosis if not accounted for.
- The normal reference range varies somewhat between laboratory assay methods.
- A normal anion gap does not exclude a mixed acid-base disorder — it only addresses the gap-forming component.
References
- Standard definition based on electroneutrality of plasma; see also Anion 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.
Pathophysiology, SGLT2i euglycemic DKA, balanced fluid resuscitation, potassium-before-insulin safety rules, dextrose addition kinetics, and subcutaneous transition.
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.
Relevant Clinical Pathways (7)
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.