Liver & KidneysNo Fasting RequiredTurnaround: 10–20 minutes (STAT bedside / emergency analyzer)

Arterial Blood Gas (ABG — pH, pO2, pCO2, Bicarbonate & Oxygen Saturation)

Also known as: ABG Test, Blood Gas Analysis, Arterial Blood Analysis, Acid-Base Gas Panel, Arterial Oxygenation Test

Parameters Measured in the Report

A breakdown of individual biomarkers and biological reference intervals typically found in your report:

Biomarker	Standard Range	Unit	What It Means
Arterial pH (Blood Acidity)	7.35–7.45 (Acidemia: < 7.35 Alkalemia: > 7.45 Critical: < 7.20 or > 7.60)	pH units	Exact hydrogen ion concentration; tightly regulated by renal bicarbonate and lung carbon dioxide exchange.
Partial Pressure of Carbon Dioxide (PaCO2) (Arterial CO2)	35.0–45.0 (Respiratory Acidosis: > 45.0 Respiratory Alkalosis: < 35.0)	mmHg	Respiratory component; elevated in hypoventilation/COPD (hypercapnia); low in hyperventilation.
Partial Pressure of Oxygen (PaO2) (Arterial O2)	80.0–100.0 (Mild Hypoxemia: 60–79 Severe Hypoxemic Failure: < 60.0)	mmHg	Actual physical pressure of dissolved oxygen in arterial blood; assesses lung alveolar gas transfer.
Arterial Bicarbonate (HCO3-) (Actual Bicarbonate)	22.0–26.0 (Metabolic Acidosis: < 22.0 Metabolic Alkalosis: > 26.0)	mEq/L (mmol/L)	Metabolic/renal component; low in metabolic acidosis (DKA, sepsis lactic acidosis); high in metabolic alkalosis.
Base Excess (BE) (Base Deficit)	-2.0 to +2.0	mEq/L	Amount of buffer base required to return pH to 7.40; negative values indicate metabolic acidosis.

* Note: Reference ranges may vary slightly between testing instruments and reagent kits. Always refer to the reference interval printed on your specific pathology report.

Clinical Focus

Arterial blood acidity (pH), partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2), calculated bicarbonate (HCO3-), and base excess.

Sample & Specimen

Arterial blood from radial or femoral artery in pre-heparinized glass syringe kept on ice

Fasting Protocol

No fasting required. Emergency critical care bedside test; record room air or oxygen delivery settings (FiO2).

Turnaround Time

10–20 minutes (STAT bedside / emergency analyzer)

What Is This Test?

An Arterial Blood Gas (ABG) analysis is an emergency diagnostic test performed on oxygenated blood collected directly from an artery (typically the radial artery at the wrist) rather than a vein. Arterial blood reflects the immediate, real-time efficiency of the lungs in oxygenating blood and removing metabolic carbon dioxide, as well as the kidneys’ capacity to buffer acid-base equilibrium. In intensive care units, emergency departments, and pulmonology wards, the ABG is the foundational tool clinicians rely upon to diagnose **hypoxemic and hypercapnic respiratory failure**, identify life-threatening metabolic acidosis (such as septic lactic acidosis or diabetic ketoacidosis), and calibrate mechanical ventilator parameters.

Why Did Your Doctor Order This Test?

Physicians routinely prescribe the Arterial Blood Gas (ABG) in the following clinical scenarios:

Acute severe respiratory distress: rapid shallow breathing, cyanosis (blue lips/fingers), gasping, or acute asthma / COPD exacerbation

Monitoring critically ill patients receiving mechanical ventilation or Non-Invasive Ventilation (BiPAP/CPAP) in the ICU

Evaluation of severe unexplained metabolic acidosis: septic shock, diabetic ketoacidosis (DKA), toxic ingestions (methanol, ethylene glycol)

Determining eligibility for long-term home oxygen therapy (LTOT) in advanced chronic obstructive pulmonary disease (COPD)

Investigating sudden unexplained confusion, lethargy, or CO2 narcosis in patients with severe lung disease

How to Prepare Before Your Test

Fasting Requirement: No fasting required. Emergency critical care bedside test; record room air or oxygen delivery settings (FiO2).

No fasting or special preparation required. This is an urgent, bedside clinical procedure.
A modified Allen’s Test is performed on the patient’s wrist prior to puncture to verify adequate collateral ulnar artery circulation.
The collecting physician must document the exact percentage of oxygen the patient is breathing (e.g., Room Air 21% FiO2, Nasal Cannula 2 L/min, or Venturi Mask).

Understanding Your Results

What higher or lower readings generally mean in clinical practice:

If Values Are Higher Than Normal

High PaCO2 (>45–50 mmHg) with low pH (<7.35) confirms Respiratory Acidosis (hypoventilation, COPD failure, narcotic overdose). Low HCO3- (<22 mEq/L) with low pH confirms Metabolic Acidosis (DKA, severe sepsis, renal failure). PaO2 <60 mmHg confirms Type 1 Hypoxemic Respiratory Failure requiring immediate oxygen therapy.

If Values Are Lower Than Normal

Low PaCO2 (<35 mmHg) with high pH (>7.45) indicates Respiratory Alkalosis (hyperventilation, panic attack, early pulmonary embolism, aspirin toxicity). High HCO3- with high pH indicates Metabolic Alkalosis (prolonged vomiting, severe diuretic overuse).

Frequently Asked Questions

Why is blood taken from an artery in the wrist instead of an arm vein for an ABG?

Veins carry deoxygenated blood that has already delivered oxygen to tissues and picked up waste products from muscles. Arteries carry freshly oxygenated blood straight from the lungs and heart, providing the true measurement of lung efficiency.

What is the "Allen’s Test" performed before an arterial blood draw?

The doctor or nurse compresses both the radial and ulnar arteries in your wrist until the hand turns pale, then releases the ulnar artery. If the hand flushes pink within 5 to 10 seconds, it proves the ulnar artery can safely supply the entire hand if the radial artery spasms.

Related Laboratory Tests

Tests frequently prescribed together or used as follow-up investigations:

Serum Electrolytes (Sodium, Potassium, Chloride, Bicarbonate)

Electrically charged mineral ions: Sodium (Na+), Potassium (K+), Chloride (Cl-), and Bicarbonate (HCO3-).

Kidney Function Test (KFT / RFT / Renal Panel)

Serum Creatinine, Blood Urea Nitrogen (BUN), eGFR (filtration rate), Uric Acid, and Electrolytes.

Complete Blood Count (CBC / Hemogram)

Counts and evaluates red blood cells, white blood cells, hemoglobin, hematocrit, and platelets.

Medical & Diagnostic Disclaimer

This guide is published for educational and patient informational purposes only. It is not a substitute for professional medical evaluation, diagnosis, or clinical advice.

A laboratory result that falls slightly outside standard statistical reference intervals does not automatically indicate disease; conversely, a normal result does not guarantee the absence of medical conditions. Only your attending physician can interpret lab findings in the context of your medical history, physical exam, and symptoms.