Anion Gap Calculator

Calculate anion gap for acid-base balance assessment and metabolic acidosis diagnosis.

Comprehensive anion gap calculations using serum electrolyte values to assess acid-base balance and diagnose metabolic disorders.

Examples

Click on any example to load it into the calculator.

Normal Anion Gap

Normal Anion Gap

Normal electrolyte values with standard anion gap.

Na+: 140 mEq/L

K+: 4 mEq/L

Cl-: 102 mEq/L

HCO3-: 24 mEq/L

Albumin: 4 g/dL

Phosphate: 3.5 mg/dL

High Anion Gap Metabolic Acidosis

High Anion Gap Metabolic Acidosis

Diabetic ketoacidosis with elevated anion gap.

Na+: 135 mEq/L

K+: 5.2 mEq/L

Cl-: 95 mEq/L

HCO3-: 12 mEq/L

Albumin: 3.8 g/dL

Phosphate: 4.2 mg/dL

Normal Anion Gap Metabolic Acidosis

Normal Anion Gap Metabolic Acidosis

Renal tubular acidosis with normal anion gap.

Na+: 138 mEq/L

K+: 3.8 mEq/L

Cl-: 110 mEq/L

HCO3-: 18 mEq/L

Albumin: 4.2 g/dL

Phosphate: 3.8 mg/dL

Metabolic Alkalosis

Metabolic Alkalosis

Vomiting-induced metabolic alkalosis.

Na+: 142 mEq/L

K+: 3.2 mEq/L

Cl-: 88 mEq/L

HCO3-: 32 mEq/L

Albumin: 4.5 g/dL

Phosphate: 3 mg/dL

Other Titles
Understanding Anion Gap Calculator: A Comprehensive Guide
Master anion gap calculations for acid-base balance assessment. Learn metabolic acidosis diagnosis, electrolyte interpretation, and clinical applications in medicine.

What is Anion Gap?

  • Definition and Basic Concept
  • Physiological Significance
  • Normal Values and Ranges
The anion gap is a calculated value used in clinical medicine to assess acid-base balance and diagnose metabolic disorders. It represents the difference between measured cations (positively charged ions) and measured anions (negatively charged ions) in the blood.
Basic Formula
The standard anion gap formula is: Anion Gap = (Na+ + K+) - (Cl- + HCO3-). This calculation helps identify unmeasured anions that may be present in metabolic acidosis.
Normal Range
The normal anion gap ranges from 8-16 mEq/L, with slight variations depending on the laboratory and measurement methods used. Values outside this range indicate potential acid-base disturbances.

Common Anion Gap Values

  • Normal anion gap: 12 mEq/L
  • High anion gap: 25 mEq/L
  • Low anion gap: 4 mEq/L

Step-by-Step Guide to Using the Anion Gap Calculator

  • Input Requirements
  • Calculation Process
  • Result Interpretation
To use the anion gap calculator effectively, you need serum electrolyte values from a basic metabolic panel or comprehensive metabolic panel. The calculator requires sodium, potassium, chloride, and bicarbonate values as minimum inputs.
Required Inputs
Essential values include sodium (Na+), potassium (K+), chloride (Cl-), and bicarbonate (HCO3-). Optional inputs include albumin and phosphate for corrected anion gap calculations.
Calculation Steps
The calculator automatically computes the anion gap using the formula: (Na+ + K+) - (Cl- + HCO3-). For corrected anion gap, it adjusts for albumin and phosphate levels.

Sample Input Values

  • Enter sodium: 140 mEq/L
  • Enter potassium: 4.0 mEq/L
  • Enter chloride: 102 mEq/L
  • Enter bicarbonate: 24 mEq/L

Real-World Applications of Anion Gap

  • Clinical Diagnosis
  • Emergency Medicine
  • Critical Care
Anion gap calculations are essential in emergency medicine, critical care, and internal medicine for diagnosing metabolic acidosis and guiding treatment decisions.
Emergency Department
In emergency settings, anion gap helps rapidly assess patients with altered mental status, suspected poisoning, or metabolic derangements.
Intensive Care Unit
In ICU settings, serial anion gap measurements help monitor treatment response and guide fluid and electrolyte management.

Clinical Scenarios

  • Diabetic ketoacidosis management
  • Toxic alcohol poisoning
  • Renal failure assessment

Common Misconceptions and Correct Methods

  • Formula Variations
  • Interpretation Errors
  • Clinical Context
A common misconception is that anion gap alone provides a complete acid-base assessment. In reality, it must be interpreted in conjunction with pH, bicarbonate, and clinical context.
Formula Considerations
Some laboratories use different formulas or include additional electrolytes. The corrected anion gap accounts for albumin and phosphate levels, providing more accurate assessment in certain conditions.
Clinical Correlation
Anion gap values must always be correlated with patient symptoms, medical history, and other laboratory values for accurate diagnosis and treatment planning.

Key Points

  • Normal anion gap doesn't exclude acidosis
  • High anion gap suggests specific causes
  • Corrected anion gap for hypoalbuminemia

Mathematical Derivation and Examples

  • Formula Derivation
  • Calculation Examples
  • Clinical Correlations
The anion gap formula is derived from the principle of electrical neutrality in body fluids. The sum of all cations must equal the sum of all anions to maintain electrical balance.
Mathematical Basis
In serum, the major measured cations are Na+ and K+, while the major measured anions are Cl- and HCO3-. The difference represents unmeasured anions or cations.
Clinical Examples
In diabetic ketoacidosis, ketone bodies (unmeasured anions) accumulate, increasing the anion gap. In renal tubular acidosis, the anion gap remains normal despite acidosis.

Calculation Examples

  • DKA: AG = (140 + 4) - (95 + 12) = 37 mEq/L
  • Normal: AG = (140 + 4) - (102 + 24) = 18 mEq/L
  • RTA: AG = (138 + 3.8) - (110 + 18) = 13.8 mEq/L