Blood oxygen saturation levels below 90 percent are considered low and may indicate serious health problems such as anemia, COPD or interstitial lung disease, explains the Mayo Clinic. Normal blood oxygen levels are between 95 to 100 percent. Having a low blood oxygen level is known as hypoxemia.
Hypoxemia may result in shortness of breath, according to the Mayo Clinic. Doctors measure blood oxygen levels most often by using a device called a pulse oximeter. Pulse oximeters can give reliable estimates of blood oxygen saturation levels when clipped onto the patient's finger. For more accurate readings of blood oxygen levels, doctors must collect a blood sample from the patient and run laboratory tests on the sample.