A pulse oximeter estimates oxygen saturation and pulse rate. It can offer a measurement, but it does not explain what is causing a result or replace a clinical assessment.
Readings can be affected
The FDA notes that circulation, skin pigmentation, skin thickness, skin temperature, tobacco use, and fingernail polish can affect accuracy. Follow the specific device instructions.
Consider the whole picture
Do not treat a single number as a diagnosis. Consider readings with symptoms and other information. A health care provider is the person who can diagnose a medical condition.
When you have questions
If a reading concerns you or you have symptoms, contact a qualified health care professional. For urgent symptoms, seek urgent or emergency care.
Source
Read the FDA Pulse Oximeter Basics. This article is educational, not medical advice.