Which pulmonary function test measures the oxygen saturation of a patient's blood?

The measurement of oxygen saturation of a patient's blood is most accurately done using pulse oximetry. This non-invasive test uses a device, typically attached to a finger or earlobe, which emits light wavelengths that measure the percentage of hemoglobin in the blood that is saturated with oxygen. A normal reading usually indicates sufficient oxygenation of the blood, crucial for assessing respiratory function and determining how well oxygen is being delivered to the body tissues.

Spirometry is primarily used to measure the amount of air a patient can inhale and exhale, helping to diagnose conditions like asthma and chronic obstructive pulmonary disease (COPD), but it does not provide information about oxygen saturation. A peak flow meter measures the maximum speed of expiration, which is important for managing asthma but again does not assess oxygen levels. A chest X-ray is an imaging test used to view the lungs and surrounding structures, helping identify abnormalities such as infections or lung disease, but it does not measure oxygen saturation directly. Therefore, pulse oximetry is the correct choice for assessing oxygen levels in the blood.