If you are in a hurry
- For a home SpO2 reading, look at the change from the person’s usual value together with symptoms such as breathlessness, rather than at the number itself.
- If alertness is abnormal, the lips look purplish, or breathing is so hard that the person cannot speak, call 119 (Japan’s emergency number) whatever the number is.
- Even if the number is good, see a doctor quickly if breathing is fast, the person is breathing with the shoulders, or speaking is difficult.
Hello. I am Shunichi Gamo, MD, PhD, a board-certified pulmonologist and the director of Sendai Airport North Clinic.
More and more people pick up a home pulse oximeter (a small device clipped on a fingertip that measures the amount of oxygen in the blood) when a cough or fever continues.
“I measured and it was 97%. I can relax now, right?”
I am often asked this. In fact, feeling reassured by this number alone is the biggest pitfall.
To state the conclusion first, home SpO2 (the proportion of oxygen in the blood) is a tool for judging by the change from the usual value together with symptoms, not by a single number. Even if the number is good, see a doctor quickly if breathing is fast, the person is breathing with the shoulders, or speaking is difficult.
In this article, as a pulmonologist, I explain how to read SpO2 numbers, how to measure correctly, what makes the numbers inaccurate, where to draw the line for seeing a doctor quickly, and points to watch for people with chronic lung conditions.
First, a note about our Sunday and holiday fever clinic. For influenza and COVID-19, PCR testing (a test that copies the virus’s genetic material to detect it) gives results the same day.
From October 4, 2026, we also run the fever clinic on Sundays and holidays
10:00 to 15:00 (no lunch break). No reservation is needed; you check in on the day. We give you the PCR result the same day. On Sundays and holidays we see fever patients only, and we do not offer regular outpatient care or IV drips. We are closed on Sunday, October 25, and from November we are open, in principle, every Sunday and holiday. Announcement: Sunday and holiday fever clinic
Shunichi Gamo, MD, PhD
Director, Sendai International Airport North Clinic
Born and raised locally, he attended Yuriage Elementary School and Yuriage Junior High School in Natori City. After graduating from Tohoku University School of Medicine, he worked at Sendai Open Hospital and Kesennuma City Hospital, and then at Tohoku University Hospital. In April 2021, in the middle of the COVID-19 pandemic, he opened Sendai International Airport North Clinic. Holding to a fever clinic that never turns patients away, he cared for well over 20,000 patients with fever in the two years before COVID-19 was moved to Class 5 under Japan’s infectious disease law.
Society memberships and board certifications
Certified Member and Board Certified Fellow, Japanese Society of Internal Medicine
Board Certified Pulmonologist, Japanese Respiratory Society
Board Certified Allergist, Japanese Society of Allergology
Board Certified Specialist, Japanese Society of Anti-Aging Medicine
PhD in Medicine (Tohoku University)
What is the point of measuring SpO2 at home?
The point of measuring at home is to get a clue that lets you notice a lack of oxygen in the body early.
According to the Japanese Respiratory Society, oxygen saturation (SpO2) is a value, checked through the skin, of what percentage of the hemoglobin (the component that carries oxygen) in the red blood cells is bound to oxygen[1]. In general, 96 to 99% is considered the standard range[1].
At the same time, the Japanese Respiratory Society also states that COVID-19 cannot be diagnosed from the number alone[2]. The number is not the answer to a diagnosis; it is one guide for looking at a person’s condition.
When using it at home, please look at these three things.
- [The number]
What is the value measured correctly at rest? How does it compare with the usual value? - [Breathing]
Is breathing fast? Is the person breathing with the shoulders? Do they run out of breath when speaking? - [Alertness and color]
Do they answer as usual when called? Do the lips or the face look unwell?
Of these, symptoms take priority over the number. The detailed dividing lines are summarized in the “Signs to see a doctor quickly” section below.
How should I read SpO2 numbers?
The clinical guide of the Ministry of Health, Labour and Welfare divides SpO2 into three bands: 96% or higher, above 93% and below 96%, and 93% or lower[3].
| SpO2 | Category in the guide | Clinical meaning |
|---|---|---|
| 96% or higher | Mild | If there are no respiratory symptoms, most people move toward recovery, but they can suddenly worsen[3] |
| Above 93% and below 96% | Moderate I | If there is breathlessness or signs of pneumonia, we watch carefully, considering hospital admission[3] |
| 93% or lower | Moderate II | A state that needs oxygen (respiratory failure); referral to a facility that can provide more advanced care is also considered[3] |
This table is the standard that health care professionals use to judge severity in the care of COVID-19 pneumonia[3]. It is not a table for judging on your own at home.
The guide also says an error of 3% is to be expected in SpO2[3]. For example, even if the display shows 94%, the real value may be off by a few percent. It is important not to be thrown by a difference of 1%.
Furthermore, for Moderate I, the guide cautions that a person may have hypoxemia (low oxygen in the blood) without complaining of breathlessness[3]. So we cannot say, “I am not in distress, so I am fine.”
Dr. GamoIf you are unsure how to read the numbers, please write down the “usual value” and “how the breathing looks” and show them to us as they are. That alone moves the examination along a great deal.
How do I measure correctly?
The key to measuring correctly is to warm the hands, sit still, and measure with nothing on the nails.
The US Food and Drug Administration (FDA) recommends keeping the hand warm and relaxed, and placing it below the level of the heart[4]. It asks that nail polish be removed from the finger being measured, and that you sit without moving the part where the device is attached[4].
- Warm the hands: if your fingertips are cold, rub them together or warm them before measuring
- Sit and rest: avoid measuring right after walking or while talking; measure after settling a little
- Clean the nails: avoid fingers with nail polish and the like; remove it before measuring
- Do not move: keep the finger and arm still, and read the number once it settles
- Measure under the same conditions: use the same device, the same finger and the same posture, at the same time of day such as morning and evening
If you keep measuring under the same conditions, you will learn the usual value. Please be sure to record a family member’s values when they are well.
What pitfalls make the numbers inaccurate?
The main causes of inaccurate numbers are cold fingertips, nail polish, body movement and skin color.
The Japanese Respiratory Society explains that accurate measurement may not be possible when body movement shifts the light emitter and receiver, when cold fingertips reduce blood flow, or when nail polish blocks the passage of light[1]. The FDA also states that poor blood flow, skin color, skin thickness and skin temperature can affect accuracy[4].
| Pitfall | What happens | What to do |
|---|---|---|
| Cold fingertips | Blood flow is low, so accurate measurement may not be possible[1] | Warm the hands and measure again[4] |
| Nail polish | The passage of light is blocked, and the number may be off[1] | Measure on a finger with the polish removed[4] |
| Body movement | The sensor position shifts and the number becomes unstable[1] | Sit without moving while measuring[4] |
| Skin color, thickness, temperature | Considered factors that affect accuracy[4] | Do not rely on the number alone; look at symptoms too[4] |
The FDA states that there is scientific evidence that accuracy may differ between people with darker skin and people with lighter skin[4]. If you have darker skin, please take symptoms seriously even when the number looks good.
Another big pitfall is that a normal number is not always reassuring. The FDA warns that some people do not have these symptoms even when their oxygen is low, and asks that the number be considered together with other information such as symptoms[4].
[Signs to see a doctor quickly] When should I hurry even if SpO2 is good?
Even if the number is good, see a doctor quickly if breathing is fast, the person is breathing with the shoulders, or speaking is difficult. This is my firm rule as a pulmonologist.
Even if SpO2 is 95% or higher, if any of these is present, please see a doctor the same day or consider calling 119.
Call 119 right away
If even one of the following applies, call 119 without hesitation, whatever the number is. This is the same at night and on holidays.
- Does not answer when called, or is dazed
- Breathing is so hard that the person cannot speak or cannot lie down
- Breathing with the shoulders, and the lips look purplish
- A seizure that does not stop
- SpO2 is 90% or lower even after measuring again, and there is also breathlessness[1]
The Japanese Respiratory Society states that with an SpO2 of 90% or lower there may be respiratory failure, in which enough oxygen cannot be delivered to the organs of the whole body, and appropriate action is needed[1].
See a doctor the same day, even at night or on a holiday
In the following cases, do not wait until morning; go to an emergency department even at night or on a holiday. If the person is in distress and cannot be moved, call 119.
- Even after warming the hands and measuring again, SpO2 stays at 93% or lower (the guide’s threshold at which oxygen is needed)[3]
- SpO2 is good, but at rest breathing is clearly faster than usual
- SpO2 is good, but the person is breathing with the shoulders or runs out of breath when speaking
- Can hardly drink, and is limp
See a doctor the same day (the next morning if it is night)
Even if breathing and alertness are maintained, in the following cases please do not wait too long, and talk to a fever clinic or similar. The earlier you are seen, the sooner the next step is decided.
- SpO2 stays above 93% and below 96% even after measuring again[3]
- A reading that stays 3 to 4% or more below the usual value (a guide for people with chronic lung or heart conditions)[1]
- Cough or fever continues, and the body feels more tired than usual
- The number is not worrying, but you feel “something is off with my breathing”
If the person’s condition changes during the night, go back to the “119” guide above at that moment and judge again.
Are the guides different for people with chronic lung or heart conditions?
Yes, they are. People with chronic lung or heart conditions may have a lower usual value, so the way of setting the standard differs.
The Japanese Respiratory Society says that for people who already have a lung disease, the judgment of the number at which to seek advice differs[2]. For people with chronic lung or heart disease, it recommends the following. When breathlessness or wheezing (a whistling breathing sound) becomes stronger and SpO2 drops 3 to 4% from the usual, contact your regular doctor or see a doctor[1].
- Ask your regular doctor for your own “usual value” and “value at which to contact them”
- Record your values when you are well, with dates
- Even if the number is the same, get in touch if breathlessness becomes stronger
- If you are in so much distress that you cannot speak, or your lips look purplish, call 119
These differ from person to person. It is safest to set your own standard with your regular doctor.
What should I tell you when I see a doctor?
At the visit, please tell us not only the number you measured but also how it has changed and how you measured it.
- How the numbers changed: for example, “97% three days ago, 95% yesterday, 93% today”
- The usual value: the SpO2 when you are well
- How you measured: the name of the device, which finger, whether the hand was warm, whether anything was on the nail
- Symptoms: breathlessness, cough, fever, and since when
- Chronic conditions and medicines: lung or heart disease, your medication notebook
Even a single sheet of notes about the numbers is a great help in the examination.
Dr. GamoSome people get anxious from “measuring too much.” A few times a day at set times is enough. Please do not chase the numbers too much; watch how the person is breathing.
Frequently asked questions
- Even if SpO2 is 97%, should I see a doctor if I am short of breath?
-
Yes, please do. Even if the number is good, if there are symptoms such as breathlessness, fast breathing, breathing with the shoulders or difficulty speaking, see a doctor the same day. If breathing is so hard that the person cannot speak, or the lips look purplish, call 119.
- Are the numbers the same on a home device and a hospital device?
-
The principle is the same, but the numbers can be off depending on how it is used and the conditions. Cold fingertips, nail polish and body movement all have an effect[1]. Keep measuring under the same conditions and use the numbers as a guide to see changes.
- My SpO2 was 94%. Do I need to see a doctor right away?
-
In the guide’s categories, 94% falls in the band above 93% and below 96%[3]. Warm your hands and measure again, and if it continues, see a doctor the same day, or the next morning if it is night. If breathlessness is strong, see a doctor right away.
- I have a chronic lung condition and my usual value is low. At what percentage should I get in touch?
-
It differs from person to person, so it is safest to decide in advance with your regular doctor. As a guide, the Japanese Respiratory Society recommends getting in touch or seeing a doctor when breathlessness becomes stronger and the value drops 3 to 4% from the usual[1].
- I became short of breath in the middle of the night and cannot decide what to do. What should I do?
-
If alertness is abnormal, breathing is so hard that the person cannot speak, or the lips look purplish, call 119 without hesitation. If the reading stays at 93% or lower even after measuring again, go to an emergency department even at night[3].
Summary: Do not rely on the number alone; watch the breathing and see a doctor early
- For a home SpO2 reading, look at the change from the person’s usual value together with symptoms such as breathlessness, rather than at the number itself.
- If alertness is abnormal, the lips look purplish, or breathing is so hard that the person cannot speak, call 119 whatever the number is.
- Even if the number is good, see a doctor quickly if breathing is fast, the person is breathing with the shoulders, or speaking is difficult.
- Warm the hands, sit and rest, and remove nail polish before measuring. Keep measuring under the same conditions.
- There are bands of 96% or higher, above 93% and below 96%, and 93% or lower, but there is an error of 3%, so do not decide from a single number[3].
- People with chronic lung or heart conditions should decide their usual value and the point at which to get in touch with their regular doctor.
- When you see a doctor, tell us how the numbers changed, how you measured, and your chronic conditions and medicines.
If you are concerned about how the breathing looks, please feel free to talk to us, even if the number is good. Please leave the medical side to us.
That’s all.
Disclaimer
This article is intended to provide general medical information and does not replace an examination, diagnosis or treatment by a doctor. The content is based on medical knowledge at the time of publication, but the appropriate response differs from person to person. If you are worried about your symptoms, please consult a medical institution.
References
- The Japanese Respiratory Society. Q28. What is a pulse oximeter? Respiratory Q&A (in Japanese). The Japanese Respiratory Society website. Accessed October 2026. https://www.jrs.or.jp/citizen/faq/q28.html
- The Japanese Respiratory Society, Committee on Pulmonary Physiology. A request regarding the use of pulse oximeters. COVID-19 (in Japanese). The Japanese Respiratory Society website. Accessed October 2026. https://www.jrs.or.jp/covid19/general/20210204155237.html
- Editorial Committee for the Clinical Guide (MHLW Health and Labour Sciences Research Group). Clinical management of patients with COVID-19, version 10.1 (in Japanese). Ministry of Health, Labour and Welfare website. 2024. https://www.mhlw.go.jp/content/001248424.pdf
- U.S. Food and Drug Administration. Pulse Oximeter Basics. FDA website. Accessed October 2026. https://www.fda.gov/consumers/consumer-updates/pulse-oximeter-basics
▶ Overview of this topic: Sunday and holiday fever clinic (from October 4, 2026, 10:00 to 15:00)
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