Anion Gap Calculator Ultimate Best Tool – BilalMD

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; with K⁺, ~12–16 mEq/L. Low albumin levels lower the measured gap; therefore, correct it when albumin is reduced.

Explore more nephrology calculators:

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)

1. Do your anion gap calculation with the formula above (your gap anion calculator handles both options).
2. If albumin is low, apply the albumin correction to avoid a false-normal result.
3. 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.