Meaning of Blood Oxygen Saturation SpO2

Blood oxygen saturation level (SpO2) is a measure of the amount of oxygen carried in the hemoglobin. SpO2 is expressed as a percentage of the maximum amount of oxygen that hemoglobin in the blood can carry. Since hemoglobin accounts for over 90% of oxygen in blood, SpO2 also measures the amount of oxygen in blood. Since each hemoglobin molecule can transport 4 oxygen molecules, if 100 hemoglobin modules carry 396 oxygen molecules, SpO2 is rated at 99%.

SpO2 for a normal healthy person at sea level should be at or above 94%. Patients with chronic pulmonary disease will try to maintain their SpO2 above 90% by using supplementary oxygen. It is important for people with breathing and heart problems to monitor their oxygen levels. Talk to your doctor to determine what is your "acceptable" SpO2 level.

There are many factors that may affect one's blood oxygen saturation level, e.g. health conditions, apnea, insufficient oxygen in air, and exercising. People living in high altitudes, such as Denver and Mexico City, would have relatively lower SpO2 levels. People with respiratory issues should be careful while visiting these places. Pilots and high altitude mountain climbers also need to know their SpO2 while working.

SpO2 refers to the oxygen saturation level obtained using pulse oximetry. This is the easiest and most common way of measuring oxygen saturation level as it is fast, inexpensive, and relatively accurate since new technologies and the use of algorithms allow for inexpensive portable units to measure Spo2 levels with a negligible error rate (2%). The other alternative is to measure the oxygen level from a blood sample, which is costly and invasive. Sometimes this may be the only option.