Arterial blood gas (ABG)
A blood test taken from an artery that reads several things at once — the blood's acidity (pH), carbon dioxide, oxygen and bicarbonate. It gives a fast, complete picture of the acid-base balance and breathing, and is used mainly in acutely unwell patients.
What it measures
An arterial blood gas is a panel run on blood drawn from an artery (usually at the wrist), giving several linked measurements together: the blood's acidity (pH), the partial pressures of carbon dioxide (CO2) and oxygen (O2), the bicarbonate level, and a derived value called base excess. Read together, these describe two things at once. First, the acid-base balance: whether the blood is too acidic (acidosis) or too alkaline (alkalosis), and whether the cause is respiratory (driven by CO2, i.e. breathing) or metabolic (driven by bicarbonate and acids like lactate or ketones). Second, oxygenation: how well oxygen is getting into the blood, which matters in lung disease and critical illness. Because it captures breathing, kidney and metabolic contributions in one snapshot, the ABG is a core test in emergency and intensive care — for severe breathlessness, a suspected diabetic ketoacidosis, sepsis, poisoning, or any seriously unwell patient. A venous blood gas is a less invasive alternative that gives most of the same information except accurate oxygen. It is not a routine screening test but a targeted one for the acutely ill.
What a high value can mean
- A high CO2 — the lungs are not clearing enough carbon dioxide (respiratory acidosis), as in severe asthma, COPD or a depressed breathing drive.
- A high pH (alkalosis) — the blood is too alkaline, from over-breathing (low CO2) or from vomiting and some metabolic causes.
- A high bicarbonate or base excess — a metabolic alkalosis, or compensation for a chronic high CO2.
What a low value can mean
- A low pH (acidosis) — the blood is too acidic; from retained CO2 (breathing) or added acid/lost bicarbonate (metabolic), e.g. diabetic ketoacidosis or lactic acidosis.
- A low bicarbonate or base excess — a metabolic acidosis.
- A low oxygen — impaired oxygenation from a lung or circulation problem.
When to discuss with a doctor
An arterial blood gas is an acute-care test, not one you would arrange for yourself — it is used when someone is seriously unwell to read their breathing and acid-base state quickly. Its findings guide urgent decisions: whether a person needs oxygen or breathing support, whether an acidosis (such as diabetic ketoacidosis, lactic acidosis or a poisoning) is present and how severe it is, and how treatment is working. Every value is interpreted together and in the clinical context — a single number in isolation means little. Mediora.AI can display the components of a blood gas alongside your electrolytes and lactate so the acid-base pattern is visible in one place, but a blood gas is ordered and interpreted within acute medical care by your treating team.