Use this anion gap calculator to do a fast anion gap calculation from routine electrolytes. Enter Na⁺, Cl⁻, HCO₃⁻ (CO₂) to calculate anion gap and flag high-anion-gap acidosis; optionally include K⁺ and an albumin-corrected value. Normal AG (without K⁺) is typically ~8–12 mEq/L without k.; with K⁺, ~12–16 mEq/L Low albumin levels lower the measured gap; therefore, correct it when albumin is reduced.
Anion Gap Calculator
If you want to know how the anion gap calculation is done we have a perfect guide.
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What is the anion gap?
- The anion gap (AG) estimates “unmeasured” anions in blood:
AG (no K⁺) = Na⁺ − (Cl⁻ + HCO₃⁻)
AG (with K⁺) = (Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻). - It helps distinguish between metabolic acidosis with high anion gap (e.g., lactate, ketones) and normal anion gap (hyperchloremic) causes.
Typical reference ranges (labs vary)
- Without K⁺: ~8–12 mEq/L (some modern analyzers report slightly lower ranges).
- With K⁺: ~12–16 mEq/L.
- If albumin is low, raise the AG by ~2.5 mEq/L for each 1 g/dL albumin below 4 (Figge correction). Hypoalbuminemia can mask a high AG.
How to use this page (best practice)
- Do your anion gap calculation with the formula above (your gap anion calculator handles both options).
- If albumin is low, apply the albumin correction to avoid a false-normal result.
- If the anion gap is high, think “unmeasured acids” (lactate, ketones, toxins). If normal, think hyperchloremic causes (e.g., RTA, diarrhea).
Worked example (simple)
Na⁺ 140, Cl⁻ 100, HCO₃⁻ 16 → AG = 140 − (100 + 16) = 24 mEq/L → high-anion-gap metabolic acidosis. If albumin were 2.0 g/dL, corrected AG ≈ 24 + 2.5 × (4 − 2) = 29 mEq/L.
Urine anion gap (UAG) quick read
- UAG = (Urine Na⁺ + K⁺ − Cl⁻).
- Negative UAG ⇒ lots of urinary NH₄⁺ (balances Cl⁻): typical of GI bicarbonate loss (e.g., diarrhea).
- Positive/zero UAG with acidosis ⇒ low NH₄⁺ excretion, suggests renal tubular acidosis (RTA).
FAQ “People also ask” For Anion Gap Calculator
How do you calculate an anion gap?
Use AG = Na⁺ − (Cl⁻ + HCO₃⁻) (most common). Some labs include K⁺: AG = (Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻). Compare your result with your lab’s reference range.
How to calculate the anion gap (step-by-step)?
Take the sodium value, subtract the sum of chloride and bicarbonate (CO₂). If albumin is low, add ~2.5 mEq/L for each 1 g/dL below 4 g/dL to get a corrected AG.
How to calculate anion gap in DKA?
Use the same formula (AG = Na⁺ − (Cl⁻ + HCO₃⁻)). DKA typically shows a high anion gap because ketone anions accumulate. Some clinicians also track the delta ratio to see if a mixed disorder is present.
How to calculate anion gap for DKA (with albumin correction)?
First, compute the measured AG, then correct for albumin if it’s low: AG_corr = AG + 2.5 × (4 − albumin[g/dL]). This prevents underestimating the gap in DKA patients with hypoalbuminemia.
How to calculate urine anion gap?
Use UAG = (Urine Na⁺ + K⁺ − Cl⁻). A negative UAG suggests high NH₄⁺ excretion (kidney responding properly; think diarrhea), while a positive/zero UAG suggests impaired NH₄⁺ excretion (e.g., RTA).
Notes & disclaimers
- Reference ranges vary by lab/method; always check your lab’s interval.
- This page is for education; it doesn’t replace clinical judgment.
Sources
- StatPearls Anion Gap & Acid–Base: formula, typical ranges, causes of high AG.
- Medscape Calculator Urine Anion Gap: formula and interpretation.
- LITFL: UAG overview; Delta ratio concept for mixed disorders.
- PMC study / Figge equation: albumin-corrected anion gap.
- Review of reference intervals: modern analyzers may report lower AG ranges.
Want to know more? We have a perfect anion gap calculator guide for you.