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Blood oxygen saturation
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Oxygen saturation is a percentage: the proportion of hemoglobin, the oxygen-carrying protein inside the red blood cell, that is occupied by oxygen.
Hemoglobin is a tetramer, meaning it is built from four pieces. Each of those subunits can carry one oxygen molecule, so the whole protein can carry four.
The four pieces work together. When the first oxygen molecule binds, the ones that follow bind more easily, and that interaction between subunits is called cooperativity.
That is where the number falls short. It does not always reflect content, which is how much oxygen the blood carries in total: in a person with anemia, who has little hemoglobin, saturation can approach 100 percent while total content is low. It is like the occupied seats on a bus: they tell you how full it is, not how many buses there are.
In brief
Oxygen saturation is the percentage of hemoglobin that is occupied by oxygen.
Hemoglobin is a tetramer, and each of its four subunits can carry one oxygen molecule.
Once the first one binds, the rest bind more easily, an interaction between subunits called cooperativity.
The number does not always reflect content: in anemia it can approach 100 percent while total content is low.
Occupied seats on a bus: it tells you how full it is, not how many buses there are.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Oxyhemoglobin Dissociation Curve, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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