Oxygen Saturation: A Guide to Laboratory Assessment

measured spectrophotometrically. (To avoid further confusion, I will use only O2sat and SO2 for the remainder of this article.) CO-oximetry, a more complex and reliable method, measures the concentration of hemoglobin derivatives in the blood, the results of which are then used to calculate various parameters such as hemoglobin derivative fractions (e.g., FO2Hb), total hemoglobin, and oxygen saturation. In most patients, the results—O2sat, SO2, and FO2Hb—from these three methods are virtually identical. But in cases of dyshemoglobinemia, some methods can yield misleading results, so health care professionals need to understand the differences between these methods and the limitations of each. This article will review the basics of oxygen-