Medical & Clinical
Anion Gap Calculator
Three electrolyte values hide a diagnosis in plain arithmetic. The anion gap is that arithmetic.
The anion gap is sodium − (chloride + bicarbonate), normally about 8–12 mEq/L (12–16 if potassium is included). A gap above 12 suggests unmeasured acids — the classic high-anion-gap metabolic acidosis pattern. Interpretation belongs to your clinician — use these numbers to ask better questions.
Gap = Na − (Cl + HCO3).
Normal: 8–12 mEq/L.
Above 12 → unmeasured acids.
Calculate Your Anion Gap
Anion Gap
What Is Anion Gap?
Blood is electrically neutral: measured cations (mostly sodium) must balance measured anions (chloride, bicarbonate) plus the unmeasured ones — proteins, phosphates, and organic acids.
The anion gap is the size of that unmeasured pool. When new acids flood in — ketoacids, lactic acid, toxins — they displace bicarbonate and widen the gap.
How It Is Calculated
Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻)
Example: Example: Na 140, Cl 104, HCO3 16 → gap 20 mEq/L (high-anion-gap acidosis)
Anion gap interpretation
| Gap | Direction |
|---|---|
| < 8 mEq/L | Low — albumin loss, paraproteins |
| 8–12 mEq/L | Normal |
| 12–20 mEq/L | High — acidosis of unknown acids |
| ≥ 20 mEq/L | Strongly abnormal — urgent workup |
Limitations
- Lab normals vary — use your laboratory's reference range.
- Low albumin shrinks the gap; correcting for albumin (add ~2.5 per 1 g/dL drop) is common practice.
- The gap is a clue, not a diagnosis — the differential belongs to a clinician.
Sources & Review
References used for this calculator’s formulas and thresholds:
Anion Gap FAQ
What is a normal anion gap?
About 8–12 mEq/L without potassium, or 12–16 when potassium is included in the calculation.
What causes a high anion gap?
The classic list: ketoacidosis, lactic acidosis, kidney failure, and toxins (methanol, ethylene glycol, salicylates).
What causes a low anion gap?
Low albumin is the most common cause, followed by paraproteins in myeloma.
Important disclaimer: Results are educational estimates, not a substitute for professional medical advice. Discuss your results with a qualified professional before making decisions.