Respiratory Health

Is Your Blood Oxygen Saturation Level Safe?

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Oxygen is vital to life. All the tissues, organs, and cells in the body require an uninterrupted supply of oxygen for their survival and function. A specific amount of oxygen is needed by the body to perform optimally. This amount, known as oxygen saturation, must be between 95% and 100%. But in people with chronic lung conditions such as asthma, chronic obstructive pulmonary disorder (COPD), and more recently COVID-19, the levels may drop below the desired levels requiring prompt medical attention.

What is oxygen saturation?

Oxygen saturation refers to the amount of oxygen bound to the hemoglobin molecules in the red blood cells (RBCs). Hemoglobin is the iron-containing protein and pigment in the RBCs that binds with oxygen. Hemoglobin carries oxygen through the bloodstream to all the cells, tissues, and organs of the body.
Oxygen saturation is expressed as arterial (SaO2) and venous (Sv02) oxygen saturation, and is an indicator of how well the oxygen from the lungs is distributed to all the cells.

What is a safe oxygen saturation level?

Oxygen saturation levels (SaO2) ranging between 95% and 100% are considered normal. SaO2 levels lower than 90% (hypoxemia) may lead to health complications and if it drops below 70%, the outcome may be fatal.
Some of the symptoms of a drop in the blood oxygen level below the normal range include rapid heartbeat, shortness of breath, chest pain, high blood pressure, dizziness and restlessness, wheezing, and headache.

Which conditions cause a dip in the levels of blood oxygen saturation?

Many conditions can interrupt the delivery of oxygen thereby lowering the blood oxygen level. For example, diseases affecting the lungs that make it hard to breathe air in and out of the lungs. Blood disorders and problems with blood circulation can prevent adequate absorption or transport of oxygen.
Some conditions that affect normal oxygen saturation includes:
  • COPD (Chronic obstructive pulmonary disease)
  • Asthma
  • Collapsed lung
  • Anemia
  • Heart disease
  • Congenital heart defects
High altitudes and strong pain medications may also cause blood oxygen levels to drop below the normal range.

Factors affecting oxygen saturation

Oxygen saturation depends on:
  • The amount of oxygen available in the air
  • The ability of oxygen molecules to reach the tiny air sacs in the lungs and diffuse into the bloodstream
  • The number of hemoglobin molecules present in the red blood cells
  • The affinity of hemoglobin towards oxygen

How is the blood oxygen saturation level measured?

Blood oxygen saturation level is measured by two metrics - Arterial blood gas test and pulse oximetry.
  • Arterial blood gas (ABG) test: ABG test is generally used to determine the function of the lungs for gaseous exchange. The test uses a blood sample drawn from an artery and hence accurately measures the oxygen saturation of arterial blood. This means that the oxygen level is checked before it enters the body tissues.
  • Pulse oximetry: This is a non-invasive test that measures the amount of oxygen carried by the blood to body tissues. The test uses a device called a pulse oximeter with a probe that can be attached to a finger or earlobe. It measures oxygen through beams of light (red light and infrared light) sent from the device. The oxygenated blood is measured in terms of absorption of infrared light.

Method of test

Normal value

Low value

Arterial blood gas test

75 to 100 mmHg

Below 60 mmHg

Pulse oximetry

95% to 100%

Below 90%

Does blood oxygen level need to be monitored?

Blood oxygen levels need not be closely monitored unless you have a health condition. In such cases, the ideal range for the specific condition will be informed by the doctor. The doctor may also prescribe supplemental oxygen if the blood oxygen levels are too low.
In recent times, blood oxygen saturation has been identified as an important vital to monitor the health of patients affected by COVID-19. Certain patients with the virus do not experience breathlessness but have been tested with significantly a low level of oxygen saturation when checked. In such cases, frequent monitoring of the blood oxygen by using a pulse oximeter can help by cautioning the patient to seek medical help before their condition worsens.


Oxygen saturation levels may go low in people with lung diseases such as COVID-19, pneumonia, COPD, and asthma. These individuals may have to test and monitor their blood oxygen levels regularly by using a pulse oximeter. Blood oxygen levels can be improved through a few self-care measures such as getting fresh air, eating healthy, and taking up regular physical activity.
If you have any questions, you can:

Talk to a COVID-19 Expert


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