Pulse Oximeter at Home: How to Use It and Understand the Reading

What a Pulse Oximeter Measures

A pulse oximeter shines light through the fingertip and estimates the percentage of haemoglobin in the blood that is carrying oxygen. This is called the oxygen saturation, usually shown as SpO₂. Most devices also display the pulse rate and, on many models, a waveform or bar that shows the strength of the pulse signal.

It is an estimate. Laboratory measurement from an artery is more accurate, and fingertip devices sold for home use vary in quality. An oximeter is therefore best used to follow trends in a person whose doctor has asked for monitoring, rather than as a diagnostic test.

Who May Be Asked to Use One

A doctor may suggest home oximetry for some people with chronic lung or heart conditions, during recovery from certain respiratory infections, or when a patient is being monitored at home after illness. If you have not been advised to monitor oxygen levels, occasional readings in a well person are rarely helpful and can cause unnecessary worry.

Step by Step: Taking a Reading

1. Sit and rest for about five minutes before measuring, unless the doctor has asked for a reading during activity.
2. Make sure the hand is warm. Rub the hands together if the fingers are cold.
3. Remove nail polish or artificial nails from the finger being used; they can block the light.
4. Place the device on a middle or index finger, with the nail facing up, and rest the hand on the chest or a table at about heart level.
5. Keep still and wait. The reading often changes during the first seconds. Wait until the numbers stop changing and the pulse signal looks strong and regular — usually at least 30 seconds to a minute.
6. Record the steady value, the pulse, the time, and whether the person was at rest or had just been active or using oxygen.

What Can Make Readings Inaccurate

• Cold hands, poor circulation or low blood pressure.
• Movement, shivering or tremor.
• Nail polish, artificial nails or dirt on the finger.
• Very bright light shining directly on the sensor.
• Skin pigmentation: pulse oximeters may overestimate oxygen levels in people with darker skin, which can make a low level look more reassuring than it is.
• Certain conditions, such as carbon monoxide exposure or severe anaemia, which the device cannot detect correctly.
• Low-quality devices that have not been tested for medical accuracy.

Understanding the Reading

Healthy people usually have oxygen saturation readings in the mid-to-high 90s. However, what counts as acceptable varies: some people with long-term lung disease normally live with lower levels, and their doctor may set a specific target range. Readings can also dip briefly with movement or a poor signal.

For this reason, the most useful information comes from comparing readings with the person's usual level and noticing a downward trend. If your doctor has asked you to monitor oxygen levels, ask them to tell you the level at which you should contact them and the level at which you should seek emergency care.

The pulse rate shown on the device can also be helpful, but irregular heart rhythms may not be counted accurately. If the pulse reading seems unusual, check it by feeling the pulse at the wrist or by using a blood pressure monitor.

When to Seek Medical Help

Contact your doctor if readings are lower than the level they have advised, are falling over time, or if breathlessness is gradually getting worse.

Related Guides

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• When Home Care Is Not Enough: Signs You Should Go to Hospital