Pulse oximetry is so commonly used in medical care that it is often referred to as the fifth vital sign besides pulse rate, body temperature, respiration rate, and blood pressure. The purpose of an oximeter reading is to measure the oxygen saturation of the blood indirectly as against a direct measurement that is done through a blood sample. Several conditions affect lung function and blood oxygen levels. A pulse oximeter is used especially in conditions such as: Pneumonia Lung cancer Asthma Chronic Obstructive Pulmonary Disease Anaemia Congenital heart disease COVID 19