Oxyhemoglobin (co-oximetry)

This test measures the fraction of your hemoglobin that is carrying oxygen, called oxyhemoglobin. It is performed by co-oximetry, a method that shines multiple wavelengths of light through a blood sample to directly determine different forms of hemoglobin.

It is usually done on a blood gas sample from an artery or sometimes from another blood source. The result reflects how much of your total hemoglobin is actually bound to oxygen at the moment of testing, taking into account abnormal forms of hemoglobin that cannot carry oxygen.

Your body relies on hemoglobin to transport oxygen to organs and tissues. The oxyhemoglobin fraction helps clinicians understand how well your blood is being oxygenated and whether problems like lung disease, heart issues, or exposure to certain chemicals are affecting oxygen delivery.

This test is often ordered along with blood gases when you have breathing difficulties, chest symptoms, or are being monitored in emergency or intensive care settings. It can be especially helpful when pulse oximetry is unreliable or when abnormal hemoglobins such as carboxyhemoglobin or methemoglobin are suspected.

A lower than expected oxyhemoglobin fraction can occur with lung conditions that limit oxygen transfer, low oxygen in the air you breathe, or circulation problems. It can also be reduced if nonfunctional hemoglobins are present, such as after carbon monoxide exposure or with certain drug effects. In contrast, supplemental oxygen or improved breathing may increase the proportion of hemoglobin carrying oxygen.

Your healthcare team will interpret this result together with your symptoms, vital signs, pulse oximetry, blood gas values, total hemoglobin, and related measurements like carboxyhemoglobin and methemoglobin. If results are outside the expected range, next steps may include adjusting oxygen therapy, checking for exposure risks, reviewing medications, or investigating lung or heart conditions. Ask your clinician what your specific result means in your situation and whether any follow-up testing is needed.