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Know Your Blood Oxygen Numbers

Nina Ghamrawi, MS, RD, CDE
January 24, 2022

Checking your blood oxygen is simple enough: just put the meter on your finger and wait, right? But how do you read the number? What does ‘low’ blood oxygen really mean? Many of our patients first diagnosed with COPD will say that their oxygen levels are always ‘low,’ but also always similar. Here’s how to know when your low blood oxygen is just your usual, or baseline, and when low oxygen is truly a risk for you.

How to Read Your Blood Oximeter and Know your Numbers

There are 2 numbers on the machine, itself: the blood oxygen (SpO2%), on the left, reading as low as 70 and up to 100%, and the Pulse rate measuring range, reading as low as 30 and up to 250 bpm (PRbpm) on the right. Besides these two numbers on your device, there’s a third number that you’ll need to know when you open the app, and that is called the ‘perfusion index.’

First, the Blood Oxygen Level

Critical Low Low Normal High Critical High
≤84.9 85-88.9 89-100 N/A N/A

Next, the Pulse Rate Range

The normal resting pulse rate is between 60 and 100 beats per minute. Many factors can influence pulse rate, including exercise, usual fitness level, emotional state, body weight, medications and body position. If you have a pulse below 50, and you are not an endurance athlete, then this may be too low for you. Follow guidelines to take a perfect oxygen reading, and call your doctor if you are concerned.

Perfusion Index

In your app, you may notice something called PI. This is the pulse strength that your machine detects. The PI ranges from 0.01%(very weak pulse strength) to 20%(very strong pulse strength). PI is a relative number and varies a lot depending on which body part you are measuring blood oxygen, and other physiologic conditions. It is meant as a guide for accuracy. If you notice that your PI is typically on the lower end, some basic things to keep in mind are:

  • Keep your hand warm
  • Keep your nails short, and make sure your fingertip is all-the-way in
  • Don’t wear nail polish

If you continue to have issues with a low PI, review the best practices for how to take a measurement and improve accuracy.

How to Take a Baseline Reading

When first starting to monitor blood oxygen, one of the most important things you could do is to check your baseline, or typical blood oxygen level. To get a baseline, check your blood oxygen saturation levels 3 times daily for the first 3 days of getting your device. Average all these readings together to get your baseline, or typical levels.

You may need to recheck your baseline when:

  • The doctor suggests to do so
  • You have a change in COPD medications
  • You have a change in health condition

What Blood Oxygen Range is Right for Me?

First ask: What is my baseline? If you know your baseline, then normal for you will be that baseline.

Oxygen Saturation What to Do:
Normal range for people without COPD:
95% and above
This is normal for people without COPD
Normal/goal for people with COPD:
88-92%, or at or above your baseline

Measure twice per day or as directed by your physician; measure especially at night.
Review trends regularly with your team.
Low for people with COPD:
86-88%, or 1% or more below your baseline.

1. Double check that you are taking the measurement correctly
2. Take oxygen or use an inhaler
3. Recheck every 30 minutes until SpO2 gets to the goal

If the current oxygen therapy or medication cannot bring the SpO2 to the goal, call emergency.
If you are not on oxygen therapy, and you are not feeling well*, contact your doctor and call emergency.
Critically Low for people with COPD:
85% and below
1. Double check that you are taking the measurement correctly
2. Take oxygen or use an inhaler
3. Call emergency if you are feeling unwell. *
4. Recheck every 15 minutes and give oxygen or use an inhaler to get blood oxygen back to baseline.

*If you are feeling fine, and have not had any symptoms in recent days, then double-check the best practices and retest immediately. Your provider will still be notified and may reach out to you to double-check, as needed.

Note: Most guidance on blood oxygen levels and risks are based on continuous blood oxygen saturation monitoring. However, iHealth blood oximeter is designed only for home SpO2 monitoring and spot-checks. As a result, home monitoring is not a replacement for emergency room care or Pulmonology specialist recommendations. If you are concerned about your results, don’t try to interpret them. Talk to your pulmonologist or regular doctor if you have questions about your condition or readings.  Always practice best practices when taking a measurement to make sure your readings are accurate. SpO2 below 80-85% may lead to brain/organ damage. If you are having any symptoms of lows, always talk to your provider.


Regardless of your oxygen levels, knowing how to read your monitor and what the numbers mean is the first way to empower you to care for your condition. You should always be aware of your symptoms, and your typical range, or baseline, as that will help you to recognize false alarms and better notify your doctor in times of urgency.