Anion Gap Calculator
Calculate serum anion gap from sodium, chloride, and bicarbonate values, used in clinical assessment of acid-base disorders. This calculator is for educational and reference purposes only.
💊 Clinical Reference📐 Anion Gap = Na⁺ - (Cl⁻ + HCO₃⁻)🏥 Health
Sodium (mEq/L)
Chloride (mEq/L)
Bicarbonate (mEq/L)
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Anion Gap Calculator | — | Anion Gap = Na⁺ - (Cl⁻ + HCO₃⁻) | mEq/L |
Step-by-Step Examples
Example 1
Normal Values
Na=140, Cl=104, HCO3=24.
- Gap = 140-(104+24) = 140-128 = 12
- Within normal reference range (8-12)
✓ Anion gap = 12 mEq/L (normal)
Example 2
Elevated Gap
Na=138, Cl=95, HCO3=15.
- Gap = 138-(95+15) = 138-110 = 28
- Significantly elevated — suggests possible metabolic acidosis with elevated unmeasured anions
✓ Anion gap = 28 mEq/L (elevated)
Example 3
Borderline High
Na=142, Cl=100, HCO3=24.
- Gap = 142-(100+24) = 142-124 = 18
- Mildly elevated, warrants clinical context evaluation
✓ Anion gap = 18 mEq/L (mildly elevated
Real-World Applications
Acid-Base Disorder Assessment
Clinicians use anion gap to help differentiate causes of metabolic acidosis.
Medical Education
Anion gap calculation is a foundational concept in nursing and medical school curricula.
Laboratory Medicine
Lab reports often include calculated anion gap alongside basic metabolic panel results.
Emergency Medicine
Rapid anion gap assessment helps guide initial differential diagnosis in acute presentations.
Common Mistakes to Avoid
⚠️
Using this as a diagnostic tool without professional interpretation
Anion gap must be interpreted in full clinical context by a healthcare provider — this calculator is for educational reference only, not diagnosis.
⚠️
Ignoring lab-specific reference ranges
Normal anion gap reference ranges vary slightly between laboratories (commonly 8-12, but some labs use 10-20 depending on methodology) due to different measurement techniques.
⚠️
Forgetting potassium in some formula variants
Some institutions include potassium in the anion gap formula (Na+K-(Cl+HCO3)), which shifts the normal range slightly higher — know which formula your reference uses.
Frequently Asked Questions
What does anion gap measure? ▾
The difference between measured cations (sodium) and measured anions (chloride + bicarbonate) in serum, representing unmeasured anions like proteins, phosphates, and organic acids.
What causes an elevated anion gap? ▾
Common causes include diabetic ketoacidosis, lactic acidosis, renal failure, and certain toxic ingestions (methanol, ethylene glycol, salicylates) — always requires professional clinical evaluation.
What is the normal anion gap range? ▾
Typically 8-12 mEq/L, though this varies by laboratory and measurement method. Some labs report slightly different ranges based on their specific equipment calibration.
Why might anion gap be falsely low? ▾
Hypoalbuminemia (low albumin) can lower the measured anion gap since albumin is a major unmeasured anion contributing to the normal gap.
Is this calculator for self-diagnosis? ▾
No — this tool is for general educational reference only. Any concerning lab values should always be discussed with and interpreted by a qualified healthcare professional.