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.
Please read this first: these results are educational estimates, not medical advice. For decisions about your health, talk to a qualified professional.