What are the causes of low blood oxygen level?

Updated June 13, 2017

Hypoxaemia, or hypoxia, is the medical term for a low oxygen level. This condition can be characterised by shortness of breath and reduced exercise capacity, with fatigue occurring quickly after physical exertion. Learning about the causes of a low blood oxygen level can help you to understand how this condition is diagnosed and treated.


Low blood oxygen levels are significant because the body's cells rely on oxygen for proper functioning. When oxygen levels are reduced, the cells cannot function normally. Tissues can also become damaged due to a lack of oxygen. Several causes of low blood oxygen levels can be life-threatening. Once the cause of hypoxaemia is identified, it should be treated to ensure that tissue damage and more serious consequences do not occur.


Low blood oxygen levels are most often caused by conditions that affect the lungs and heart. The Mayo Clinic reports that respiratory conditions that contribute to hypoxaemia include airway obstruction, chronic obstructive pulmonary disease (COPD), emphysema, interstitial lung disease, pneumonia and blood clots in the lungs. Cardiac causes of low blood oxygen levels include low cardiac output and birth defects of the heart. Other causes of hypoxaemia include anaemia, shock, sleep apnoea and living or visiting areas with high altitudes.


Hypoxaemia can be diagnosed with an arterial blood gas test or the use of a pulse oximeter. Arterial blood gas testing involves taking a sample of blood from an artery. The sample is analysed to determine the concentration of oxygen and carbon dioxide present. Pulse oximeters are medical devices that measure the concentration of oxygen in the blood. If the level of oxygen in the blood is low, further testing may be needed to determine the cause of the hypoxaemia. Computerised tomography (CT) scanning and magnetic resonance imaging (MRI) can be used to diagnose heart and lung conditions that may be causing hypoxaemia. Specialised tests such as pulmonary function testing, electrocardiography and echocardiography may also be used to check the structure and function of the heart or lungs.


Oxygen treatment is used to increase the amount of oxygen in the bloodstream and lungs. This reduces the symptoms associated with low blood oxygen levels. Portable oxygen tanks make it possible to receive this treatment at home instead of in the hospital. The University of Michigan Health System indicates that oxygen gas cylinders, oxygen concentrators and liquid oxygen devices can be used to administer oxygen to patients with low blood oxygen levels. Treating the underlying cause of hypoxaemia can help prevent low blood oxygen levels from occurring consistently.


Prolonged periods of low blood oxygen levels can be very serious. In addition to tissue damage, hypoxaemia can cause life-threatening complications. Geoff Bellingan, a senior lecturer at the Centre for Respiratory Research at the Rayne Institute in London, reports that low blood oxygen levels result in an inflammatory response by the body. This results in leaks in the tiny blood vessels known as capillaries. If hypoxaemia persists, fatal pulmonary or cardiac complications may occur.

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About the Author

Leigh Zaykoski has been a writer and editor for six years. Her medical writing has appeared on dozens of websites. Zaykoski attended the University of Pittsburgh and Keystone College, studying microbiology and business administration. She is currently pursuing a medical writing certification.