An arterial blood gas (ABG) test is a vital diagnostic tool that measures the levels of oxygen, carbon dioxide, and blood pH — providing invaluable insight into lung function and acid-base balance. Whether you’re a patient preparing for the test or a family member seeking clarity, this guide will walk you through everything you need to know.

What Is an Arterial Blood Gas Test?

An ABG test analyzes a small sample of arterial blood — usually drawn from the wrist — to assess how well your lungs are oxygenating blood and removing carbon dioxide, as well as how your kidneys and buffers are managing the body’s acid-base balance.

Definition and Purpose

Purpose: Evaluate respiratory function and metabolic status.
Key Measurements: pH (acidity), PaO₂ (arterial oxygen pressure), PaCO₂ (arterial carbon dioxide pressure), HCO₃⁻ (bicarbonate), and O₂ saturation.

Indications for ABG Testing

Common Clinical Indications

Respiratory distress (e.g., COPD exacerbation, asthma attack)
Suspected acid–base disorders (metabolic acidosis/alkalosis)
Monitoring ventilated patients in the ICU
Assessment before major surgery in patients with lung or heart disease

Preparation and Procedure

Patient Preparation

Explain the procedure and obtain consent.
Avoid nicotine or caffeine 30 minutes prior, as they can alter respiratory rate.
Ensure hemodynamic stability (blood pressure and circulation adequate).

Performing the ABG Sample Collection

Site selection: Radial artery is preferred (Allen’s test first to confirm collateral circulation).
Skin antisepsis to reduce infection risk.
Needle insertion at a 45° angle into the artery, drawing 1 mL of blood.
Apply pressure for at least 5 minutes (longer if on anticoagulants).
Label and transport sample on ice to the lab within 15 minutes.

Understanding Normal ABG Values

Parameter	Normal Range
pH	7.35 – 7.45
PaO₂	80 – 100 mm Hg
PaCO₂	35 – 45 mm Hg
HCO₃⁻	22 – 26 mEq/L
O₂ Saturation	95 – 100 %

Why These Values Matter

pH: Overall acid–base status
PaO₂: Efficiency of oxygen uptake
PaCO₂: Respiratory component of acid–base balance
HCO₃⁻: Metabolic component of acid–base balance

Interpretation of ABG Test Results

Acid–Base Disorders

Acidosis vs. Alkalosis: pH <7.35 indicates acidosis; pH >7.45 indicates alkalosis.
Primary vs. Compensation: Determine whether the disturbance is respiratory (PaCO₂) or metabolic (HCO₃⁻).

Respiratory vs. Metabolic Imbalances

Respiratory acidosis: Elevated PaCO₂ (e.g., COPD flare).
Metabolic acidosis: Low HCO₃⁻ (e.g., diabetic ketoacidosis).
Mixed disorders: Both components abnormal—requires careful analysis.

Risks and Complications

Arterial spasm or thrombosis at puncture site
Hemorrhage or hematoma if pressure application is inadequate
Infection (rare with proper aseptic technique)

Conclusion

The arterial blood gas (ABG) test is an indispensable tool for diagnosing and managing respiratory and metabolic disorders. Familiarity with the procedure, normal values, and interpretation can empower you to engage more effectively with your healthcare team.

Resources:

Mayo Clinic – Arterial Blood Gas Test:
https://www.mayoclinic.org/tests-procedures/arterial-blood-gas/about
American Association for Respiratory Care – ABG Analysis
National Heart, Lung, and Blood Institute – Blood Gas Analysis:
https://www.nhlbi.nih.gov/health-topics/blood-gas-analysis

ABG Test Arterial Blood Gas Lung Function

Arterial Blood Gas (ABG) Test Explained: Procedure, Normal Values & Interpretation