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Blood Gas Analysis/Arterial Blood Gas, ABG

Arterial Blood Gas (ABG) is a blood test that measures the levels of oxygen (O₂), carbon dioxide (CO₂), and acid-base balance (pH) in your blood. It is taken from an artery, usually at the wrist, and is a crucial tool to understand how well your lungs and kidneys are functioning in maintaining the body’s internal balance.

Why is ABG Done?

ABG helps to evaluate:

How well oxygen is entering the blood from the lungs.
How well carbon dioxide is being removed.
The acidity or alkalinity (pH) of your blood.
How your lungs and kidneys respond to illness.

It is used in emergencies and chronic diseases like:

COPD, asthma, or lung failure.
Severe infections, pneumonia, or sepsis.
Ketoacidosis, renal failure, or shock.
Monitoring patients on ventilators or oxygen therapy.

How to prepare for the test?

There is no special preparation which is usually needed before the test.
You should inform the doctors if you are on blood thinners.
You have to stay still during the test as the movement may make it harder to draw arterial blood.

How the Test is done?

A small needle is inserted into an artery, commonly the radial artery at the wrist.
Then that site may be numbed with local anesthesia.
The blood is drawn into a syringe and immediately sent to the lab.
A pressure bandage is applied afterward to avoid bruising or bleeding.
The test is quick (usually <5 minutes), though a bit more painful than a vein sample.

What It Measures?

pH – Acid-base balance (normal: 7.35–7.45)
PaO₂ – Partial pressure of oxygen
PaCO₂ – Partial pressure of carbon dioxide
HCO₃⁻ (Bicarbonate) – Buffer that maintains pH
O₂ Saturation – How much oxygen your blood is carrying

Frequently Asked Questions (FAQs)

1. Is ABG more painful than other blood tests?

Yes, because it’s drawn from an artery which lies deeper and under higher pressure, it may feel sharper than a regular blood test.

2. Can ABG results change quickly?

Yes, ABG reflects your current respiratory and metabolic status, so the results may vary based on breathing rate, oxygen levels, or illness progression.

3. What’s the difference between ABG and pulse oximetry?

Pulse oximetry only measures the oxygen saturation, while ABG gives detailed information on oxygen, carbon dioxide, and pH balance.

4. Are there any risks or side effects?

You might have a temporary pain, bruising, or bleeding. Serious complications are rare but can include arterial injury or poor blood flow in people with circulation issues.

Blood Gas Analysis/Arterial Blood Gas, ABG)