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Arterial blood gas (ABG) test
Category: Biopsies, Lab & Pathology Tests · All biopsies, lab & pathology tests
What it is
An arterial blood gas measures oxygen, carbon dioxide and acidity (pH) in arterial blood, plus calculated values such as bicarbonate. It shows how well the lungs are exchanging gas and how the body is balancing acid and base — essential in acute illness and respiratory medicine.
Why it is done
It is used in breathlessness and respiratory failure assessment, COPD exacerbations (to detect carbon dioxide retention), severe infections and sepsis, diabetic emergencies, kidney and metabolic problems, and intensive care monitoring.
How to prepare
Tell the clinician about blood thinners and any fistula in the arm (dialysis patients — the fistula arm must not be used). If you are on oxygen, the amount is recorded with the sample because it changes interpretation. An Allen test may check hand circulation first.
What happens during the procedure
The sample is taken from an artery — usually the wrist (radial artery), sometimes the groin or elbow — with a fine needle into a heparinised syringe. It is more uncomfortable than a venous blood test; local anaesthetic is sometimes used. Pressure is applied for several minutes afterwards and the sample goes on ice or straight to the analyser.
Afterwards — recovery & results
Results are available within minutes and are acted on by the treating team the same day — for example adjusting oxygen or starting non-invasive ventilation in COPD. You simply keep pressure on the site and report increasing pain, swelling or hand paleness.
Risks & considerations
Risks include bruising/haematoma, pain, and very rarely artery spasm or damage affecting hand circulation (checked beforehand and monitored). Venous blood gas is a less painful alternative that answers many (not all) of the same questions.
Watch: Arterial blood gas (ABG) test videos
Real procedure videos from the MedicalVideos.com library. Some clinical footage is graphic — that is the nature of a medical video library.
Related guides on MedicalVideos.com
Frequently asked questions
Why arterial, when veins are easier?
Only arterial blood shows what the lungs have just delivered — oxygen levels and the true gas exchange picture. Venous values differ, though they approximate pH and CO2 reasonably.
Why does it hurt more than a blood test?
Arteries are deeper, muscular and pressure-filled, with more nerve supply around them. A skilled operator and, where offered, local anaesthetic reduce this considerably.
Related procedures — Biopsies, Lab & Pathology Tests
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