Anion Gap Calculator
Calculate anion gap from sodium, chloride, and bicarbonate with optional potassium mode and albumin correction. This page supports interpretation planning, not independent diagnosis.
Medical Disclaimer
This calculator is educational and does not diagnose disease or replace clinician-guided acid-base assessment.
Calculate Anion Gap
Your Results
Formula Used
Input summary: Na 140, Cl 104, HCO3 24, albumin 4 g/dL.
Recommendations
- Use local laboratory reference interval for final interpretation.
- Track trend over repeated panels under similar conditions.
- Correlate with blood gas and clinical findings when acid-base concern persists.
Interpretation and Follow-up Checklist
Interpretation Checklist
- Interpret AG with blood gas, clinical status, and trend, not as a standalone diagnosis.
- Use albumin correction when low albumin may hide a higher effective gap.
- Confirm whether your workflow reports AG with or without potassium.
- Correlate with lactate, ketones, renal function, and toxin exposure risk when indicated.
Follow-up Checklist
- Repeat chemistry panel under comparable conditions if result is unexpected.
- Document hydration status, medications, and clinical symptoms with lab values.
- Use clinician-guided recheck intervals for metabolic-acid-base follow-up.
- Seek urgent care for severe symptoms or rapid deterioration.
Reference Context
This page uses common reference bands (8 to 12 mmol/L (without K)), but local laboratory method and institutional protocol should take priority.
Medical Note
This calculator provides educational interpretation support only and is not an emergency triage, diagnosis, or treatment tool.
Editorial & Review Information
Reviewed on: 2026-02-24
Published on: 2025-10-05
Author: LumoCalculator Editorial Team
Editorial review: Formula mode wording, albumin-correction language, interpretation boundaries, and source-link stability reviewed for C-phase consistency.
Purpose and scope: Supports adult educational interpretation of AG trend and context. Not an emergency triage, prescribing, or diagnosis engine.
Use Scenarios
Scenario 1: Chemistry panel review
Use AG as a structured check when reviewing sodium, chloride, and bicarbonate from routine or acute chemistry panels.
Scenario 2: Low albumin context
Apply albumin correction when albumin is reduced to avoid underestimating high-gap metabolic context.
Scenario 3: Follow-up trend planning
Track AG trend over repeated panels and bring results into clinician discussions with symptom and treatment timeline.
Formula Explanation
Core Structures
Anion gap is a practical estimate of unmeasured ions and is widely used in acid-base evaluation. The selected formula mode must match your local workflow because reference bands differ when potassium is included.
Albumin contributes significantly to unmeasured anion context. When albumin is low, uncorrected AG can appear deceptively low. Albumin correction helps reduce that underestimation risk in many clinical situations.
AG is not a standalone diagnosis. Interpretation quality improves when AG is integrated with blood gas, lactate, ketones, renal profile, medication context, and clinical presentation.
How to Interpret AG Safely
Keep formula mode consistent
Do not compare a K-inclusive AG against a K-exclusive reference band. Keep formula and reference style aligned.
Use correction when justified
In low-albumin settings, corrected AG can better reflect effective gap context than uncorrected AG.
Correlate with acid-base data
Pair AG with blood gas and broader metabolic findings to avoid overinterpreting one metric.
Avoid self-treatment decisions
Use outputs for discussion support, not independent treatment adjustments.
Example Cases
Case 1: Typical AG without correction
Input: Na 140, Cl 104, HCO3 24 (without K). AG = 12. This is near upper typical band for K-excluded mode and can serve as baseline trend context.
Case 2: Low albumin unmasking context
Input: Na 140, Cl 100, HCO3 16, albumin 2.0. Base AG = 24; corrected AG = 29. Correction highlights a stronger high-gap context.
Case 3: K-inclusive workflow
Input: Na 138, K 4.8, Cl 102, HCO3 23. K-inclusive AG = 17.8. Compare using K-inclusive reference band rather than K-excluded range.
Common Input Mistakes and Practical Fixes
Mistake 1: Mixing formula styles
Fix: decide K-inclusive or K-exclusive mode before trend comparison and keep it consistent.
Mistake 2: Skipping albumin context
Fix: check albumin when AG interpretation is clinically important, especially if albumin may be low.
Mistake 3: One-panel conclusions
Fix: use repeated chemistry trends and clinical trajectory instead of isolated panels.
Mistake 4: Ignoring urgent symptoms
Fix: escalate urgent symptoms immediately; calculators do not replace emergency assessment.
8-Week Metabolic Follow-up Framework
Weeks 1-2: Baseline capture
Record chemistry values, AG mode, albumin context, symptoms, and medication timeline before drawing trend conclusions.
Weeks 3-6: Consistent execution
Maintain comparable sampling conditions and document relevant changes in hydration, diet, treatment, and illness course.
Weeks 7-8: Recheck and align
Reassess AG trend with clinician guidance and decide whether additional acid-base testing or targeted etiologic workup is needed.
Boundary Conditions
- Designed for educational adult interpretation context, not pediatric-specific protocols.
- Not intended for emergency triage or immediate treatment directives.
- Reference ranges vary across analyzers and lab protocols.
- Albumin correction is an estimate and does not replace full acid-base assessment.
- Not a prescribing tool and not a substitute for clinician diagnosis.
- When clinical judgment conflicts with calculator output, clinical judgment prevails.
Sources & References
- Figge J et al. (1998) - Serum proteins and acid-base equilibria - Foundational support for albumin-aware interpretation and correction context.
- Merck Manual Professional - Metabolic Acidosis - Clinical overview of metabolic-acid-base mechanisms and interpretation pathways.
- MedlinePlus - Electrolyte Panel - Patient-facing laboratory context for sodium, chloride, and bicarbonate interpretation.
- NIDDK - Kidney Failure - Kidney-dysfunction context relevant to high-gap metabolic patterns.
- WHO - Diabetes Fact Sheet - Public-health context for hyperglycemic crises that may involve high-gap acidosis.