Pulse oximetry is a noninvasive screening test used to measure which of the following?

• A. Respiratory rate
• B. Oxygen saturation of the tissues
• C. Heart rate
• D. Blood pressure

Answer: (B)

Pulse oximetry is used to estimate how much oxygen is bound to hemoglobin in the arterial blood, i.e., the oxygen saturation (SpO2). The device shines light through a fingertip (or earlobe) and measures how much light is absorbed by oxyhemoglobin versus deoxyhemoglobin. From that, it provides a percentage that reflects how well oxygen is being carried to the tissues. This is why the test is described as measuring oxygen saturation. It doesn’t directly measure respiratory rate or blood pressure, though many monitors may also display heart rate as a byproduct of the pulse signal. A normal reading is typically around 95–100%, with lower values suggesting potential hypoxemia and the need for assessment or intervention.