Oxygen is the gas of life. It’s essential for the bulk of life processes and adequate functioning of the different cells, tissues, and systems of the body. 

The ideal level of oxygen in the blood for an adult is between 90/95-100%; anything lower than 88% points to a condition called hypoxia. Hypoxia is classed by the blood oxygen level being too low. It’s hazardous to health as it kills the tissues of the brain, lungs, and heart. That’s why it’s important to consistently measure blood oxygen levels if you have a reason to need to. 

Early detection of low oxygen levels can prevent health-related complications and allow for timely administration of artificial oxygen.

There are two key ways of checking blood oxygen levels:

  • Pulse Oximetry
  • Blood Gas test

Pulse Oximetry

This method is non-invasive and involves the use of a device called a pulse oximeter to measure the oxygen saturation in arterial blood, offering an instant reading. This method is fast, easy and also provides a heart rate measurement.

Mode of Action

The pulse oximeter functions on the unique principle of light absorption by the blood. When clipped to the patient’s finger, the clip of the pulse oximeter shines a broad spectrum light through the finger. As oxygenated and deoxygenated blood absorbs light at different wavelengths, the device can determine blood oxygen levels through a diode at the other end, which checks the wavelength at which the patient’s blood absorbs the light. A reference curve saved into the device’s memory allows it to calibrate its readings, thus giving accurate results. A pulse oximeter must be calibrated properly to work – see here for more details: https://www.sensoronics.com/pages/guide-to-correctly-calibrating-oxygen-sensors


  • Ergonomic; can be operated with little instruction
  • Results are obtained promptly
  • The device itself is very portable and readily available in physical and online health stores
  • Non-invasive
  • Also checks your heart rate


Readings are affected by:

  • Pulse and blood flow to the fingers
  • Cold hands, dehydration, and dirty probe
  • The patient moving excessively during the test.
  • Nail varnish and false nails.
  • Anemia
  • Raynaud’s syndrome

Blood Gas Test

As the name implies,a blood gas test checks the levels of certain gases in the blood. Asides from being a more accurate measure of blood oxygen levels, this test also indicates the level of carbon dioxide in the blood and how efficiently your lungs are exchanging oxygen and carbon dioxide. The test also indicates the pH of the blood. There are two forms of the blood gas test:

  • Arterial blood gas test, where the blood sample is taken from the wrist or insides of the elbow
  • Capillary blood gas test, when the sample is taken from the earlobe


  • Results are more accurate
  • Readings are not affected by the physical conditions of the patient (temperature, blood flow, etc.)
  • Also checks blood levels of carbon dioxide


  • More invasive than pulse oximetry.
  • Can’t be performed at home
  • Can’t be used when you’re unwell or have conditions like COPD (Chronic Obstructive Pulmonary Disease), pulmonary fibrosis, pulmonary hypertension, etc.