Carboxyhemoglobin is a compound formed when carbon monoxide (CO) binds to hemoglobin in red blood cells. Hemoglobin is responsible for transporting oxygen throughout the body, but when it binds with carbon monoxide, it reduces the blood's ability to carry oxygen. This can lead to serious health issues, including tissue damage and even death, depending on the level of exposure. The presence of carboxyhemoglobin in the blood can be measured through a blood test. High levels are often associated with carbon monoxide poisoning, which can occur from sources like faulty heaters, car exhaust, or smoke inhalation. Prompt treatment is essential to prevent severe complications.