In children, the normal pulse ox reading that measures the amount of oxygen in the blood is 96 to 98 percent, states AboutKidsHealth. Anything under 95 percent is abnormally low and may cause doctors to order additional testing, states Children's National Health System.
The pulse ox, or pulse oxidation, test measures oxygen saturation with a device that shines a red light through the child's finger or toe where the detector on the other side measures the oxygen levels, states AboutKidsHealth. Doctors use this test to detect congenital heart disease in infants, according to Children's National Health System. Other possible causes of low blood oxygen levels, or hypoxemia, include asthma attacks, anemia and lung diseases, states WebMD.