You can use the spo2 reading to determine whether there’s a risk that you may be having a medical emergency such as a heart attack or stroke. In general, it’s good to see over 95% of the oxygen in the blood but less than 100%. The “sweet spot” is said to be 98-100%, although there are many factors that influence this number. Feel free to follow up with your doctor if you receive an alarmingly low reading. It's not uncommon to see lower levels when you're active. however, if the number remains low after you've stopped moving for at least 10 minutes, it could be a sign of a problem. Spo2 levels also depend on the region of the body where they're measured.