How do you calculate the anion gap?

Use AG = Na+ − (Cl− + HCO3−). Optionally include potassium: AG = (Na+ + K+) − (Cl− + HCO3−). Enter lab values in mmol/L to get the result.

What is a normal anion gap?

Typical reference ranges are 8–12 mmol/L without potassium and 12–16 mmol/L when potassium is included. Always interpret with your laboratory’s reference interval.

When should I correct the anion gap for albumin?

Correct for albumin when hypoalbuminemia is suspected, because low albumin can mask a true high anion gap. A common correction is: Corrected AG = AG + 2.5 × (4.0 − albumin[g/dL]).

What does a high anion gap mean?

A high anion gap suggests an anion gap metabolic acidosis. Common causes include ketoacidosis, lactic acidosis, renal failure, and toxic ingestions such as methanol or ethylene glycol. Immediate evaluation is recommended.

What does a normal anion gap indicate?

A normal anion gap may be seen in non-anion gap (hyperchloremic) metabolic acidosis. Typical causes include diarrhea, renal tubular acidosis, and excessive normal saline infusion.

What does a low anion gap mean?

A low anion gap is uncommon and may reflect lab error, hypoalbuminemia, or paraproteinemia. Repeating the test and checking albumin or total protein can be helpful.

Should I include potassium in the anion gap calculation?

Including potassium is optional. Many labs report AG without potassium; including it slightly raises the normal range. Be consistent with your institution’s convention.

Anion Gap Calculator – Fast Results & Medical Guide

Q: What is the anion gap?

The anion gap (AG) is a calculated value used to help identify metabolic acidosis. It represents the difference between measured cations (mainly sodium, optionally potassium) and measured anions (chloride and bicarbonate) in serum.

Anion Gap Calculator

Enter serum values to calculate the Anion Gap.
AG = Na⁺ – (Cl⁻ + HCO₃⁻)

Na⁺

Cl⁻

HCO₃⁻

Include Potassium (K⁺)

Correct for Albumin

Serum electrolytes panel for anion gap calculation (Na, Cl, HCO3, optional K) — Suggested header image: clean medical banner with test tubes/electrolyte icons (keep < 200 KB, ALT above).

Anion Gap Calculator – A Complete Guide for Clinicians & Students

The Anion Gap (AG) is a core tool to identify and classify metabolic acidosis. Calculated from routine electrolytes, it reveals unmeasured ions that hint at critical underlying processes. Our calculator above provides fast results with optional potassium inclusion, albumin correction, and instant interpretation with next steps.

Use the calculator ↑ • Then return here for interpretation and learning.

What is the Anion Gap?

The Anion Gap represents the difference between measured cations and measured anions in serum, helping detect unmeasured ions associated with acidosis.

Standard (without potassium): AG = Na⁺ − (Cl⁻ + HCO₃⁻)

With potassium included: AG = (Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻)

Anion gap formula diagram showing cations (Na±K) versus anions (Cl + HCO3) — Suggested image: simple infographic of the AG formula with cations and anions in contrasting colors.

Normal Reference Ranges

Method	Normal Range (mmol/L)
Without Potassium	8 – 12
With Potassium	12 – 16

Always check your laboratory’s reference interval before interpretation.

Why Calculate the Anion Gap?

Differentiate anion gap metabolic acidosis (AGMA) from non–anion gap metabolic acidosis (NAGMA).
Identify or exclude urgent causes (DKA, lactic acidosis, renal failure, toxins).
Guide targeted diagnostics and management.

Key Features of Our Anion Gap Calculator

Dual Modes: with or without K⁺.
Albumin Correction: Corrected AG = AG + 2.5 × (4.0 − albumin[g/dL]).
Color-coded Interpretation: Low, Normal, or High.
Actionable Tips: “What to do next” for each category.
Mobile-friendly UX and quick input flow.

Screenshot of the Anion Gap Calculator interface — Suggested image: cropped screenshot of your calculator UI.

How to Use the Calculator

Enter Sodium (Na⁺), Chloride (Cl⁻), and Bicarbonate (HCO₃⁻) in mmol/L.
(Optional) Include Potassium (K⁺).
(Optional) Add Albumin to apply correction.
Click Calculate to get AG, corrected AG (if applicable), and interpretation.

Step 1 — Enter values

Type your Na⁺, Cl⁻, and HCO₃⁻. Optionally include K⁺ and albumin for correction.

Na⁺(+ K⁺)Cl⁻HCO₃⁻

Tip: Typical example — Na 140, Cl 104, HCO₃ 24.

Step 2 — Calculate AG

AG = Na⁺ (+ K⁺) − Cl⁻ + HCO₃⁻

AG = measured cations minus measured anions.

Step 3 — Read the result

Example: AG 14 mmol/L — Normal

Ref: 8–12 (no K⁺) · 12–16 (with K⁺). High AG → consider DKA, lactic acidosis, renal failure, toxins.

Interpreting Results

Low Low Anion Gap (rare): consider lab error, hypoalbuminemia, paraproteinemia. Action: repeat labs; check albumin and protein.

Normal Normal Anion Gap: often hyperchloremic (non-anion gap) metabolic acidosis. Action: assess for diarrhea, renal tubular acidosis, saline overload.

High High Anion Gap: suggests metabolic acidosis. Action: evaluate for life-threatening etiologies promptly (see mnemonic below).

MUDPILES mnemonic graphic for high anion gap causes — Suggested image: MUDPILES (or GOLDMARK) mnemonic as a simple, branded card.

Common Causes of High AG (MUDPILES)

Methanol
Uremia
Diabetic ketoacidosis
Propylene glycol
Iron/Isoniazid
Lactic acidosis
Ethylene glycol
Salicylates

FAQs (Quick Answers)

Should I include potassium in AG calculation?: Optional. Many labs report AG without K⁺. Including K⁺ slightly raises the normal range—be consistent with local convention.
Why correct for albumin?: Low albumin lowers the AG and can mask acidosis. Correcting AG improves diagnostic accuracy.
Is this calculator suitable for pediatrics?: Yes, but neonates/infants may have different reference ranges. Interpret with age-appropriate norms.
Does this tool replace clinical judgment?: No. Use alongside clinical evaluation and local protocols; repeat labs if results are discordant with the presentation.

References

Kraut JA, Madias NE. Serum anion gap: Its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162–174. doi: 10.2215/CJN.03020906
Emmett M, Narins RG. Clinical use of the anion gap. Medicine (Baltimore). 1977;56(1):38–54.
Story DA. The meaning of the anion gap. Anaesth Intensive Care. 2004;32(5):575–578.

Educational use only. Not a substitute for professional medical advice.