Anion Gap Calculator
Enter electrolyte values in mEq/L. This tool estimates the anion gap and provides a basic interpretation.
What is the anion gap?
The anion gap (AG) is a quick clinical calculation used to help evaluate acid-base disorders, especially metabolic acidosis. It compares measured positive ions (cations) and negative ions (anions) in blood chemistry.
In practical terms, an elevated anion gap suggests that unmeasured acids are present in the blood. Common examples include lactic acidosis, ketoacidosis, and renal failure-related acid retention.
Formulas used in anion gap cálculo
Standard formula (without potassium)
AG = Na - (Cl + HCO3)
Alternative formula (including potassium)
AG = (Na + K) - (Cl + HCO3)
Albumin-corrected anion gap
Albumin is a major unmeasured anion. If albumin is low, the measured AG may appear falsely normal. A common correction is:
Corrected AG = AG + 2.5 × (4.0 - albumin)
This correction is most useful in patients with hypoalbuminemia (for example, malnutrition, liver disease, or critical illness).
How to interpret results
- Without potassium: typical reference range is about 8 to 12 mEq/L (lab dependent).
- With potassium: typical reference range is about 12 to 16 mEq/L.
- High AG: often indicates additional unmeasured acids.
- Normal AG acidosis: can occur in bicarbonate loss states (e.g., diarrhea, renal tubular acidosis).
- Low AG: less common; consider lab artifact, hypoalbuminemia, paraproteinemia, or intoxications.
Common causes of high anion gap metabolic acidosis
Frequently remembered categories
- Lactic acidosis (sepsis, shock, hypoperfusion)
- Diabetic ketoacidosis, alcoholic ketoacidosis, starvation ketosis
- Advanced kidney failure (uremic acids)
- Toxin ingestion (methanol, ethylene glycol, salicylates)
Step-by-step example
Suppose labs show: Na 140, Cl 104, HCO3 18.
- AG = 140 - (104 + 18)
- AG = 140 - 122 = 18 mEq/L
An AG of 18 is above the usual range (without potassium), suggesting a high anion gap process. Clinical context and additional tests are always required to identify the exact cause.
Important limitations
- Reference ranges vary by laboratory and analyzer method.
- The AG is a screening tool, not a final diagnosis.
- Albumin level can significantly affect interpretation.
- Always interpret with blood gas data, clinical exam, and other chemistry results.
Quick FAQ
Is a higher anion gap always dangerous?
Not always, but it should be evaluated promptly because it may indicate serious underlying conditions.
Should potassium be included?
Many clinicians use the formula without potassium. Either method can be acceptable if interpreted with the matching reference range.
Can this calculator replace medical advice?
No. This tool is educational and cannot replace clinician judgment, formal diagnosis, or emergency care.