Pulse oximeter: how to read it, accuracy limits, and when to call
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- Zacurate 500 Series fingertip pulse oximeter. Best for: Simple spot checks at home. See options on Amazon
- Fingertip oximeter with waveform and alarm. Best for: People tracking a lung condition with their provider. See options on Amazon
- Bluetooth fingertip pulse oximeter. Best for: Logging readings in an app. See options on Amazon
What a pulse oximeter does
The FDA describes a pulse oximeter as a device usually placed on a fingertip that uses light beams to estimate the oxygen saturation of the blood and the pulse rate, without drawing blood. MedlinePlus explains that a sensor measures the light passing through your skin, and after a few seconds the device shows your heart rate and oxygen level. The light may make your fingertip look red, but it does not hurt.
MedlinePlus says an at-home oximeter may be helpful if you have a serious or chronic lung disease, and that your provider can guide you on buying and using one.
MedlinePlus lists reasons a provider may check oxygen with pulse oximetry, including conditions that affect lung function such as COPD, lung cancer, heart failure, asthma and COVID-19; taking medicine for lung disease; surgery; sleep apnea; oxygen therapy, to check the flow rate; and shortness of breath.
What the numbers mean
| SpO2 reading | What MedlinePlus says | Action |
|---|---|---|
| 95% to 100% | Normal oxygen saturation | Keep tracking as advised |
| Somewhat lower | May be acceptable with lung disease such as COPD, or at high elevation | Follow your provider's target |
| 92% or lower | Contact your provider | Call your provider |
| 88% or lower | Seek immediate medical attention | Get care now |
MedlinePlus adds that results may be 2% to 4% higher or lower than your actual blood oxygen level, and a blood test called an arterial blood gas is more accurate.
What affects accuracy
The FDA says that although pulse oximetry is useful for estimating blood oxygen, oximeters have limitations and a risk of inaccuracy. Factors it lists include poor circulation, skin pigmentation, skin thickness, skin temperature, current tobacco use and fingernail polish. MedlinePlus also mentions dark nail polish, artificial nails, darker skin pigmentation, poor circulation, cold skin and tobacco use.
The FDA has studied ongoing concerns that oximeters may be less accurate in people with darker skin, and in January 2025 proposed updated recommendations for testing and labeling to improve performance across skin tones.
How to take a reading at home
- Remove nail polish or artificial nails from the finger you use, since both can affect the reading, per MedlinePlus.
- Warm your hands if they are cold, since cold skin and poor circulation affect accuracy.
- Rest and keep still while the device reads; wait a few seconds for the number to settle.
- Write it down with the time, so you and your provider can see trends.
The FDA says if you use a pulse oximeter at home and are concerned about the reading, contact a health care provider, and do not rely only on the oximeter.
Symptoms matter more than the number
MedlinePlus lists signs of low oxygen to watch for with an at-home oximeter: lips, nails or face that look bluish, trouble breathing or shortness of breath, chest pain or tightness, and a fast heart rate. The FDA says to keep track of how you feel and contact a provider if symptoms are serious or get worse. Get emergency help for severe trouble breathing or bluish lips, whatever the oximeter shows.
Choosing a home oximeter
Most home units are fingertip clips. Listings commonly mention extras such as a waveform display (plethysmograph), alarms, rechargeable batteries or app tracking; pick the features your provider wants you to use for logging. Some oximeters are sold for sports and wellness rather than medical use. If you are monitoring a health condition, ask your provider which type to buy, as MedlinePlus suggests. For other home tools, see our upper arm blood pressure monitor guide and heart rate monitor guide.
What to look for when you buy
Zacurate 500 Series fingertip pulse oximeter
Best for: Simple spot checks at home
A fingertip clip that shows SpO2 and pulse rate, the two readings the FDA describes.
Watch out: Remove nail polish and warm cold hands before reading.
See options on AmazonFingertip oximeter with waveform and alarm
Best for: People tracking a lung condition with their provider
Innovo lists a plethysmograph (waveform) display and an alarm on its iP900 models.
Watch out: Do not rely only on the number; track symptoms too, per the FDA.
See options on AmazonBluetooth fingertip pulse oximeter
Best for: Logging readings in an app
App logging makes it easier to share trends with your provider.
Watch out: Check whether it is sold for medical or wellness use.
See options on AmazonQuestions people ask
- What is a normal pulse oximeter reading?
- MedlinePlus says normal oxygen saturation is 95% to 100%.
- When should I call a doctor about my oxygen level?
- Contact your provider at 92% or lower; seek immediate care at 88% or lower.
- How accurate are pulse oximeters?
- Readings may be 2% to 4% off, and the FDA lists factors such as skin pigmentation, circulation and nail polish that affect accuracy.
- Does nail polish affect a pulse oximeter?
- Yes. MedlinePlus says dark nail polish can block the light.
- Can I rely on a pulse oximeter alone?
- No. The FDA says track your symptoms and contact a provider if they are serious or worsen.
Sources
- Pulse Oximeters (fda.gov), U.S. Food and Drug Administration
- Pulse Oximetry (medlineplus.gov), MedlinePlus, U.S. National Library of Medicine