Clinical Decision-Making

How to Interpret ABG Results: A Clinical Framework

Master arterial blood gas interpretation with this systematic approach to acid-base disorders.

Quick Medical Calculator Team · December 11, 2025 · 3 min read

Arterial blood gas (ABG) analysis is fundamental to critical care and emergency medicine. This guide provides a step-by-step approach to ABG interpretation.

The 5-Step Approach

Step 1: Assess Oxygenation

Look at PaO2 first:

  • Normal: 80-100 mmHg
  • Hypoxemia: < 80 mmHg

Step 2: Determine pH Status

  • Normal pH: 7.35-7.45
  • Acidemia: pH < 7.35
  • Alkalemia: pH > 7.45

Step 3: Identify Primary Disorder

Compare pH with PaCO2 and HCO3:

DisorderpHPaCO2HCO3
Respiratory Acidosis↓↑Normal initially
Respiratory Alkalosis↑↓Normal initially
Metabolic Acidosis↓Normal initially↓
Metabolic Alkalosis↑Normal initially↑

Step 4: Check for Compensation

The body attempts to normalize pH:

  • Respiratory disorders → Metabolic compensation (takes days)
  • Metabolic disorders → Respiratory compensation (takes hours)

Step 5: Calculate Anion Gap

For metabolic acidosis, calculate: Anion Gap = Na - (Cl + HCO3)

Normal: 8-12 mEq/L

Clinical Pearls

  1. Always correlate with clinical presentation
  2. Consider mixed disorders
  3. Use the delta-delta ratio for complex cases
  4. Remember: compensation never over-corrects

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