A pulse oximeter estimates peripheral oxygen saturation (SpO₂); it does not diagnose why oxygen is low and it does not prescribe oxygen. The FDA warns that readings can be inaccurate under some circumstances.
First: check whether the reading is technically believable
Rest, keep the hand still and allow the reading to stabilize. Poor circulation, skin temperature, movement, nail products, device quality and other factors can affect readings. The FDA also notes evidence of performance differences related to skin pigmentation, which is one reason a single number should not be interpreted in isolation.
Look at symptoms and trends, not only one number
A persistent change from a person's usual readings may be more informative than a single transient value. Record the reading, symptoms, activity at the time and whether supplemental oxygen was being used as prescribed. Follow the individual's clinician-provided action plan.
Why there is no safe universal internet threshold for every person
Clinical oxygen targets and escalation plans can differ, especially in chronic lung disease. ATS home-oxygen guidance defines clinical criteria for particular patient groups, while individual treatment still requires professional assessment. Do not use a generic web threshold to start oxygen or alter a prescribed flow.
When the number and the person disagree
If someone looks seriously unwell despite a reassuring number, seek medical assessment. Conversely, an unexpectedly low reading in someone who feels well should be repeated carefully and discussed with a clinician if it persists. A pulse oximeter is an aid to assessment, not a replacement for it.
What a pulse oximeter cannot tell you
- The cause of breathlessness
- Whether carbon dioxide is high or low
- Which oxygen concentrator capacity to buy
- The correct oxygen flow for an individual
- Whether CPAP or BiPAP is required
Related Respmart guidance
Sources and evidence
- FDA: Pulse Oximeter Basics
- FDA: Pulse Oximeters for Medical Purposes draft guidance
- ATS: Home Oxygen Therapy for Adults
Medical note: This article is general education, not diagnosis or a prescription. Oxygen is a medical treatment. Use it only as prescribed and do not change flow, duration or delivery mode without the treating clinician. Severe or rapidly worsening breathing difficulty, chest pain, confusion, bluish lips or collapse needs urgent medical care.
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