How accurate is a pulse oximeter? American Thoracic Society

How accurate is the pulse oximeter? 

• A pulse oximeter may also be less accurate with very low oxygen saturation levels (below 80%) or with very dark skin.
• False high readings are also always obtained from smokers - readings are affected for up to four hours after smoking a cigarette (Dobson, 1993).
• Most oximeters give a reading 2% over or 2% under what your saturation would be if obtained by an arterial blood gas. For example, if your oxygen saturation reads 92% on the pulse oximeter, it may be actually anywhere from 90 to 94%. 

• https://www.thoracic.org/patients/patient-resources/resources/pulse-oximetry.pdf
• Pulse Oximetry | Measuring Oxygen Status | Nursing Times
• Pulse oximetry (nih.gov)