O2Hb Mixed

O2Hb Mixed measures the fraction of hemoglobin in a mixed venous blood sample that is bound to oxygen. Mixed venous blood is typically obtained from a pulmonary artery catheter, which blends venous blood returning from the entire body and provides a global picture of oxygen balance.

The test is performed by co-oximetry on a blood gas analyzer, which distinguishes oxyhemoglobin from other hemoglobin species. It differs from arterial oxygen saturation or pulse oximetry because it reflects what oxygen remains after tissues have extracted what they need.

This test helps your care team assess whether your body is receiving and using enough oxygen overall. It is often used in critical care, after major heart surgery, in shock, in heart failure, and during complex procedures where oxygen delivery and demand can shift quickly.

Lower results may suggest reduced oxygen delivery or increased tissue demand. Higher results can occur when tissues cannot use oxygen effectively or when delivery exceeds current needs. Your team looks at trends alongside vital signs, hemoglobin level, and cardiac output to guide decisions about fluids, medications, ventilation, and transfusion.

Your result is interpreted together with where the sample was drawn, your hemoglobin level, your breathing support, and your overall condition. A true mixed venous sample comes from a pulmonary artery catheter; central venous samples are related but not identical. Co-oximetry also reports other hemoglobin forms, such as carboxyhemoglobin and methemoglobin, which can influence interpretation.

If your value is unexpected, your clinicians may verify the sampling site, repeat the test, or check related measures like arterial blood gases, lactate, and cardiac output. Follow-up focuses on the cause, which may include improving oxygen delivery, reducing excess demand, or addressing problems with how tissues use oxygen.