Which of the following is NOT a vital sign?

Pulse oximetry measures the oxygen saturation level in the blood, which indicates how well oxygen is being transported throughout the body. While it is an important assessment tool in monitoring a patient's respiratory function and overall health, it is typically categorized as a diagnostic test rather than a traditional vital sign. The conventional vital signs include temperature, blood pressure, pulse (heart rate), and respiratory rate, which are routinely measured to assess the patient's immediate physiological status. Therefore, selecting pulse oximetry as the answer accurately identifies it as the option that does not fit into the standard list of vital signs.