Some first responders have the ability to measure carboxyhemoglobin in the blood using a device called a pulse carbon monoxide oximeter. Specifically, the pulse CO-oximeter measures the saturation of carbon monoxide in the hemoglobin (SpCO). It uses light waves (usually shone through the fingertips) to measure carbon monoxide saturation noninvasively.
Another form of noninvasive measurement uses exhaled air to determine levels of carbon monoxide. Some research has found exhaled CO to be inaccurate as a determinate of carbon monoxide poisoning.
Traditional pulse oximetry, used to measure only whether hemoglobin is saturated with oxgyen or not, is fooled by carbon monoxide poisoning into showing artificially high saturation of oxygen when carboxyhemoglobin is present. This makes it even more important to obtain a good history and physical examination of the patient.