What is PO2 in a Blood Test?

PO2, or partial pressure of oxygen, in a blood test measures the amount of oxygen dissolved in your blood. This indicates how well your lungs are taking in oxygen and your blood is carrying it. It's a crucial part of an arterial blood gas (ABG) test, which assesses your blood's oxygen and carbon dioxide levels, and its acidity (pH).

• What it measures: PO2 specifically reflects the pressure exerted by dissolved oxygen gas in your blood, not the total amount of oxygen present. A small percentage (1-2%) of the total blood oxygen is actually dissolved; the majority is bound to hemoglobin. [Source: Radiometer]
• How it's used: Doctors use PO2 levels to diagnose and monitor various respiratory and circulatory conditions. Low PO2 (hypoxemia) suggests problems with oxygen uptake in the lungs or oxygen delivery to the tissues. [Source: Cleveland Clinic, Mount Sinai]
• Normal range: A typical normal range for PO2 is 80-100 mmHg (millimeters of mercury), or 10.5-13.5 kPa (kilopascals). This can vary slightly depending on the lab and individual factors. [Source: Mount Sinai, Iowa State University] However, values outside this range may indicate issues that require further medical examination. [Source: Medical News Today]
• Related Tests: PO2 is often measured alongside other parameters like PCO2 (partial pressure of carbon dioxide) and blood pH in an ABG test to get a complete picture of respiratory function. [Source: GLOWM, NCBI Bookshelf]

Where PO2 is Measured

PO2 is most accurately measured from an arterial blood sample because arterial blood carries oxygen from the lungs to the body's tissues. While samples from arterialized sites like earlobes can be used, they may not provide the same accuracy. [Source: PubMed]

Example: A PO2 reading of 60 mmHg suggests hypoxemia, potentially indicating lung disease, heart failure, or other underlying health problems requiring further investigation.