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The ratio of the substance fraction of oxyhemoglobin to the substance fraction of all forms of hemoglobin. This quantity takes into account the effects of abnormal hemoglobins such as carboxyhemoglobin, methemoglobin, or sulfhemoglobin. Thus, in the presence of abnormal hemoglobins, the fractional oxyhemoglobin may be decreased while the oxygen saturation is normal.
See also: oxyhemoglobin