According to Minnesota Dept. of Health:
A normal level of oxygen is usually at least 95% or higher. Some people with chronic lung disease or
sleep apnea can have normal levels of around 90%. The SpO2 reading on a pulse oximeter shows the
percentage of oxygen in someone’s blood.
The instructions that came with my home-use pulse oximeter (in German) roughly ...
Yes, it is absolutely possible. There are several poisons, most notably cyanide, which interfere with the body's ability to take up or use oxygen from the blood, despite it being present in ample amounts to otherwise support life. This is known as histotoxic hypoxia.
As an example, a telltale sign of cyanide poisoning is a flushing of the skin, turning deep ...