According to the Mayo Clinic, a normal pulse oximeter reading ranges from 95 to 100 percent; any value under 90 percent is considered to be a low reading. A low reading likely means that a person has hypoxemia or low blood oxygen.
About.com states that those with chronic respiratory illnesses often have hypoxemia. A pulse oximetry test is a non-invasive and pain-free test that measures the amount of hemoglobin combined with oxygen in the arterial blood of a patient. There are home pulse oximeters available, but there is a risk for a false reading in some cases. They may also be ineffective during circumstances that cause poor circulation.