Anion Gap Calculator: Acid-Base Balance in Blood

Understanding the Anion Gap

The serum Anion Gap (AG) is a critical calculation used in medicine to identify the cause of metabolic acidosis (lower than normal blood pH). It measures the difference—or "gap"—between the primary measured cations (positively charged ions) and primary measured anions (negatively charged ions) in the blood serum.

🩸 Anion Gap Calculator

Input your BMP lab values to instantly calculate the serum anion gap without risky manual errors.

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🔬 The Clinical Formula

Anion Gap = Sodium (Na⁺) - [Chloride (Cl⁻) + Bicarbonate (HCO₃⁻)]

*Note: Some institutions include Potassium (K⁺) in the calculation, but the standard simplified version omits it. A normal anion gap is typically between 8 to 12 mEq/L. Read more at the National Library of Medicine.

📝 Usage Guide

✔️ Enter Sodium (Na⁺): Input the patient's sodium level in mEq/L or mmol/L.
✔️ Enter Chloride (Cl⁻): Input the serum chloride level.
✔️ Enter Bicarbonate (HCO₃⁻): Input the total CO2 or bicarbonate level.
✔️ Hit Calculate: Instantly receive the Anion Gap value.

🏥 ER Case Example

A patient presents to the ER with diabetic ketoacidosis (DKA). Their lab results show Na⁺ = 140, Cl⁻ = 100, and HCO₃⁻ = 15.

Anion Gap = 140 - (100 + 15) = 140 - 115 = 25 mEq/L

Because 25 is far above the normal upper limit of 12, the patient has a High Anion Gap Metabolic Acidosis (HAGMA), confirming the DKA.

❓ FAQ

What is the mnemonic for HAGMA?

Medical students commonly use MUDPILES: Methanol, Uremia, DKA, Paraldehyde, Iron/Isoniazid, Lactic acidosis, Ethylene glycol, and Salicylates.

Why is albumin important?

Albumin makes up the bulk of the unmeasured anions. If a patient has hypoalbuminemia (low albumin), you must calculate a "corrected anion gap."

Understanding the Anion Gap