{
  "registry": "KnowYourPrime Evidence Registry",
  "license": {
    "name": "CC BY 4.0",
    "url": "https://creativecommons.org/licenses/by/4.0/",
    "attribution": "Credit KnowYourPrime and link to the finding URL."
  },
  "fields": {
    "devices": "Devices this finding names, including models it says it does not cover. What was actually tested is in scope.applies_to; exclusions are in scope.does_not_cover.",
    "evidence": "Studies by role: anchor (the rating rests on it), conflicting, null_result, supporting.",
    "industry_ties": "Device-maker ties listed in Europe PMC metadata: author_affiliations names makers an author lists as an affiliation, funders names makers listed as funding. stated_ties holds ties a paper states only in its own conflict, funding or acknowledgement text, each read from that statement and worded to say only what it says. Sources are Europe PMC metadata, funding printed in the abstract, and those reviewed statements. An empty list means no tie was found there, not that the study is independent: many papers have no open full text to read. Metadata, not a judgment of the study. checked false means no Europe PMC metadata was available."
  },
  "id": "KYP-ER-0001",
  "version": "1.1",
  "reviewed": "2026-10-25",
  "url": "https://knowyourprime.com/evidence-wearable-blood-oxygen-accuracy",
  "title": "Smartwatch Blood Oxygen (SpO2) Accuracy Against Arterial Blood (SaO2)",
  "question": "Do consumer smartwatches and rings measure blood oxygen saturation (SpO2) closely enough to arterial blood oxygen (SaO2) to be meaningful?",
  "measurement": "Blood oxygen (SpO2)",
  "devices": [
    "Apple Watch",
    "Samsung Galaxy Watch",
    "Withings ScanWatch",
    "Garmin"
  ],
  "rating": {
    "label": "Uncertain",
    "code": "uncertain",
    "definition": "Evidence is conflicting, inconsistent, or difficult to interpret.",
    "rule_version": "1.4",
    "rule_reasons": [
      "Anchor-grade evidence affirms the core relationship.",
      "Multiple supporting studies are consistent with the core relationship.",
      "An anchor study is present but its own reported finding does not cleanly affirm this claim, so it does not count toward the Established threshold.",
      "A clean anchor supports this claim, but an unresolved conflicting study contradicts it on the core relationship, so the evidence is treated as in genuine dispute.",
      "Some evidence conflicts on secondary points that do not change the core direction."
    ]
  },
  "conclusion": "At normal and moderately low oxygen levels, some tested watches land close to a medical reference, but the evidence splits by device and by how low oxygen falls. Two Garmin models failed their tests outright, and an Apple Watch Series 7 lost accuracy once oxygen fell well below normal, which is where the reading matters most.",
  "reasoning": [
    "SpO2 is the estimate a pulse oximeter makes from light passing through skin; SaO2 is the oxygen saturation of arterial blood measured directly by a blood gas analyzer. The question is how close the first comes to the second when the sensor is on a wrist or finger ring rather than a clinical finger clip.",
    "Several direct tests affirm close agreement. Under deliberately induced low oxygen, an Apple Watch 8, a Samsung Galaxy Watch 5 and a Withings ScanWatch all stayed within the 4 percent accuracy limit that medical oximeters must meet, and in hospital patients with a COPD flare an Apple Watch 6 differed from arterial blood by less than half a percentage point on average.",
    "Other tests contradict it. A Garmin fenix 6 failed its pre-set accuracy criteria for blood oxygen under every condition tested, and a Garmin Forerunner 245 read too high more than half the time at simulated altitude. An Apple Watch Series 7 study found the error grew once saturation fell below 88 percent. Because the evidence contains both clean affirmations and core-hitting contradictions, the rule treats it as genuinely disputed and rates it Uncertain."
  ],
  "key_results": [
    {
      "text": "Apple Watch 8, Samsung Galaxy Watch 5 and Withings ScanWatch all met the 4 percent root-mean-square limit of ISO 80601-2-61 against a Masimo Radical-7, at normal oxygen and below 90 percent saturation, in 18 healthy adults; Apple Watch 8 had the lowest bias.",
      "source": "doi:10.3390/s23229164",
      "source_url": "https://doi.org/10.3390/s23229164",
      "source_citation": "Walzel et al., Sensors, 2023"
    },
    {
      "text": "In 167 patients with an acute COPD flare, Apple Watch 6 differed from arterial blood by a mean of 0.458 percent (SD 2.78, limits of agreement -5.9 to 5.0) and correlated with a medical pulse oximeter at r = 0.89. Patients whose watch needed more than 2 minutes or eight attempts were excluded.",
      "source": "doi:10.1007/s11845-023-03456-w",
      "source_url": "https://doi.org/10.1007/s11845-023-03456-w",
      "source_citation": "Arslan et al., Irish Journal of Medical Science, 2024"
    },
    {
      "text": "Below 88 percent saturation, Apple Watch Series 7 had a root-mean-square error of 5.82 percent against 3.52 percent for a clinical finger oximeter, and landed within 2 percent of arterial blood 32.14 percent of the time against 49.03 percent. Both devices overestimated oxygen.",
      "source": "doi:10.2196/85253",
      "source_url": "https://doi.org/10.2196/85253",
      "source_citation": "Jiang et al., JMIR Formative Research, 2026"
    },
    {
      "text": "Garmin fenix 6 failed to measure blood oxygen accurately under any condition, with a concordance correlation of 0.10 against a medical-grade oximeter, below the study's pre-set threshold of 0.7.",
      "source": "doi:10.3390/s25010275",
      "source_url": "https://doi.org/10.3390/s25010275",
      "source_citation": "Carrier et al., Sensors, 2025"
    },
    {
      "text": "Garmin Forerunner 245 read blood oxygen higher than the reference with an error rate above 50 percent overall and above 80 percent at simulated altitudes over 4,800 m, in 10 healthy adults.",
      "source": "doi:10.1055/a-1337-2790",
      "source_url": "https://doi.org/10.1055/a-1337-2790",
      "source_citation": "Hermand et al., International Journal of Sports Medicine, 2021"
    }
  ],
  "scope": {
    "applies_to": "Wrist-worn and ring-worn consumer pulse oximeters compared with arterial blood gas or a clinical reference oximeter, in healthy adults under induced low oxygen and in hospital patients. Device-level results apply only to the models named.",
    "does_not_cover": "Apple Watch Series 9 and later, Ultra models and the US version that calculates on the paired iPhone, none of which has a published independent test; diagnosis of any condition; children; finger-clip oximeters except as references."
  },
  "limitations": [
    "Most tests are small, from 10 to 18 healthy adults under induced low oxygen; the largest clinical sample is 167 patients with one condition.",
    "Accuracy depends on how low oxygen goes, and several studies did not test below 88 to 90 percent, where clinical decisions are made.",
    "One of the main reference oximeters is made by Masimo, a company in patent litigation with Apple over the blood oxygen feature.",
    "Skin pigmentation was not tested in the arterial blood studies cited here. One cited Apple Watch study tested it against a fingertip oximeter in 49 patients and found no significant difference in error across skin tone groups (Jiang et al., PLOS Digital Health, 2023); see the related finding on skin tone."
  ],
  "evidence": {
    "anchor": [
      {
        "key": "doi:10.2196/85253",
        "title": "Performance of Wearable Pulse Oximetry During Controlled Hypoxia Induction: Instrument Validation Study.",
        "first_author": "Jiang",
        "journal": "JMIR formative research",
        "year": 2026,
        "url": "https://doi.org/10.2196/85253",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1007/s11845-023-03456-w",
        "title": "Accuracy of the Apple Watch in measuring oxygen saturation: comparison with pulse oximetry and ABG.",
        "first_author": "Arslan",
        "journal": "Irish journal of medical science",
        "year": 2024,
        "url": "https://doi.org/10.1007/s11845-023-03456-w",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.5664/jcsm.11178",
        "title": "Performance of a commercial smart watch compared to polysomnography reference for overnight continuous oximetry measurement and sleep apnea evaluation.",
        "first_author": "Browne",
        "journal": "Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine",
        "year": 2024,
        "url": "https://doi.org/10.5664/jcsm.11178",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": [
            "funding statement: six authors had a Samsung Electronics research grant"
          ]
        }
      },
      {
        "key": "doi:10.3390/s23229164",
        "title": "Evaluation of Leading Smartwatches for the Detection of Hypoxemia: Comparison to Reference Oximeter.",
        "first_author": "Walzel",
        "journal": "Sensors (Basel, Switzerland)",
        "year": 2023,
        "url": "https://doi.org/10.3390/s23229164",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.2196/27503",
        "title": "Validation of the Withings ScanWatch as a Wrist-Worn Reflective Pulse Oximeter: Prospective Interventional Clinical Study.",
        "first_author": "Kirszenblat",
        "journal": "Journal of medical Internet research",
        "year": 2023,
        "url": "https://doi.org/10.2196/27503",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [
            "Withings"
          ],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1016/j.sleh.2022.04.003",
        "title": "Performance evaluation of a wrist-worn reflectance pulse oximeter during sleep.",
        "first_author": "Jung",
        "journal": "Sleep health",
        "year": 2022,
        "url": "https://doi.org/10.1016/j.sleh.2022.04.003",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [
            "Samsung Electronics"
          ],
          "funders": [
            "Samsung"
          ],
          "stated_ties": []
        }
      }
    ],
    "conflicting": [
      {
        "key": "doi:10.3390/s25010275",
        "title": "Validation of Aerobic Capacity (VO2max) and Pulse Oximetry in Wearable Technology.",
        "first_author": "Carrier",
        "journal": "Sensors (Basel, Switzerland)",
        "year": 2025,
        "url": "https://doi.org/10.3390/s25010275",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1016/j.mcpdig.2024.02.001",
        "title": "Accuracy of Smartwatch Pulse Oximetry Measurements in Hospitalized Patients With Coronavirus Disease 2019",
        "first_author": "K. Rajakariar",
        "journal": "Mayo Clinic Proceedings Digital Health",
        "year": 2024,
        "url": "https://doi.org/10.1016/j.mcpdig.2024.02.001",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1055/a-1337-2790",
        "title": "Accuracy and Reliability of Pulse O2 Saturation Measured by a Wrist-worn Oximeter.",
        "first_author": "Hermand",
        "journal": "International journal of sports medicine",
        "year": 2021,
        "url": "https://doi.org/10.1055/a-1337-2790",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.4187/respcare.07670",
        "title": "Reliability of Smartphone Pulse Oximetry in Subjects at Risk for Hypoxemia.",
        "first_author": "Modi",
        "journal": "Respiratory care",
        "year": 2021,
        "url": "https://doi.org/10.4187/respcare.07670",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      }
    ],
    "supporting": [
      {
        "key": "doi:10.1007/s10439-025-03936-3",
        "title": "An Adjustable Smart Ring to Monitor Pulse Rate and Peripheral Blood Oxygen Saturation.",
        "first_author": "Montenegro",
        "journal": "Annals of biomedical engineering",
        "year": 2026,
        "url": "https://doi.org/10.1007/s10439-025-03936-3",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.2196/81955",
        "title": "Reliability and Safety of Smartwatch Blood Pressure and Oxygen Saturation Measurements in Older Adults: Instrument Validation Study.",
        "first_author": "Madeira",
        "journal": "JMIR formative research",
        "year": 2026,
        "url": "https://doi.org/10.2196/81955",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1007/s10877-024-01229-z",
        "title": "Clinical evaluation of a smart wristband for monitoring oxygen saturation, pulse rate, and respiratory rate.",
        "first_author": "Monnink",
        "journal": "Journal of clinical monitoring and computing",
        "year": 2025,
        "url": "https://doi.org/10.1007/s10877-024-01229-z",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1109/embc58623.2025.11252834",
        "title": "Continuous SpO 2 Monitoring Using Reflectance Pulse Oximetry at the Wrist and Upper Arm During Overnight Sleep Apnea Recordings.",
        "first_author": "Adam",
        "journal": "Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference",
        "year": 2025,
        "url": "https://doi.org/10.1109/EMBC58623.2025.11252834",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.3390/s25051286",
        "title": "Evaluation of Pulse Oximetry Accuracy in a Commercial Smartphone and Smartwatch Device During Human Hypoxia Laboratory Testing.",
        "first_author": "Browne",
        "journal": "Sensors (Basel, Switzerland)",
        "year": 2025,
        "url": "https://doi.org/10.3390/s25051286",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [
            "Samsung"
          ],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.4187/respcare.11258",
        "title": "The Accuracy of Readily Available Consumer-Grade Oxygen Saturation Monitors in Pediatric Patients.",
        "first_author": "Kovesi",
        "journal": "Respiratory care",
        "year": 2024,
        "url": "https://doi.org/10.4187/respcare.11258",
        "industry_ties": {
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          "author_affiliations": [],
          "funders": [],
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        }
      },
      {
        "key": "doi:10.1249/mss.0000000000003460",
        "title": "Validation of Polar Elixir™ Pulse Oximeter against Arterial Blood Gases during Stepwise Steady-State Inspired Hypoxia.",
        "first_author": "Russell",
        "journal": "Medicine and science in sports and exercise",
        "year": 2024,
        "url": "https://doi.org/10.1249/MSS.0000000000003460",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [
            "Polar Electro"
          ],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.7759/cureus.35355",
        "title": "Accuracy of the Apple Watch Oxygen Saturation Measurement in Adults: A Systematic Review",
        "first_author": "Paul Y. Windisch",
        "journal": "Cureus",
        "year": 2023,
        "url": "https://doi.org/10.7759/cureus.35355",
        "industry_ties": {
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          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1371/journal.pdig.0000296",
        "title": "Investigating the accuracy of blood oxygen saturation measurements in common consumer smartwatches",
        "first_author": "Yihang Jiang",
        "journal": "PLOS Digital Health",
        "year": 2023,
        "url": "https://doi.org/10.1371/journal.pdig.0000296",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.4187/respcare.09795",
        "title": "Pulse Oximeter Performance, Racial Inequity, and the Work Ahead.",
        "first_author": "Okunlola",
        "journal": "Respiratory care",
        "year": 2022,
        "url": "https://doi.org/10.4187/respcare.09795",
        "industry_ties": {
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          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1080/02701367.2020.1759768",
        "title": "Accuracy and Reliability of Commercial Wrist-Worn Pulse Oximeter During Normobaric Hypoxia Exposure Under Resting Conditions.",
        "first_author": "Lauterbach",
        "journal": "Research quarterly for exercise and sport",
        "year": 2021,
        "url": "https://doi.org/10.1080/02701367.2020.1759768",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1186/s12890-019-1007-3",
        "title": "A multicentre prospective observational study comparing arterial blood gas values to those obtained by pulse oximeters used in adult patients attending Australian and New Zealand hospitals.",
        "first_author": "Pilcher",
        "journal": "BMC pulmonary medicine",
        "year": 2020,
        "url": "https://doi.org/10.1186/s12890-019-1007-3",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1097/aln.0000000000002002",
        "title": "Four Types of Pulse Oximeters Accurately Detect Hypoxia during Low Perfusion and Motion.",
        "first_author": "Louie",
        "journal": "Anesthesiology",
        "year": 2019,
        "url": "https://doi.org/10.1097/ALN.0000000000002002",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1213/ane.0000000000001300",
        "title": "The Accuracy of 6 Inexpensive Pulse Oximeters Not Cleared by the Food and Drug Administration: The Possible Global Public Health Implications.",
        "first_author": "Lipnick",
        "journal": "Anesthesia and analgesia",
        "year": 2017,
        "url": "https://doi.org/10.1213/ANE.0000000000001300",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1097/00000539-200210000-00033",
        "title": "\"Motion-resistant\" pulse oximetry: a comparison of new and old models.",
        "first_author": "Barker",
        "journal": "Anesthesia and analgesia",
        "year": 2002,
        "url": "https://doi.org/10.1097/00000539-200210000-00033",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1016/s0147-9563(98)90086-3",
        "title": "Meta-analysis of arterial oxygen saturation monitoring by pulse oximetry in adults.",
        "first_author": "Jensen",
        "journal": "Heart & lung : the journal of critical care",
        "year": 1999,
        "url": "https://doi.org/10.1016/s0147-9563(98)90086-3",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1016/s0735-6757(99)90019-0",
        "title": "Pulse oximetry: principles and limitations.",
        "first_author": "Sinex",
        "journal": "The American journal of emergency medicine",
        "year": 1999,
        "url": "https://doi.org/10.1016/s0735-6757(99)90019-0",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "pmid:8914569",
        "title": "Accuracy of pulse oximetry in pigmented patients.",
        "first_author": "Bothma",
        "journal": "South African medical journal = Suid-Afrikaanse tydskrif vir geneeskunde",
        "year": 1997,
        "url": "https://pubmed.ncbi.nlm.nih.gov/8914569/",
        "industry_ties": {
          "checked": false
        }
      },
      {
        "key": "doi:10.1111/j.1365-2044.1991.tb09410.x",
        "title": "Potential errors in pulse oximetry. I. Pulse oximeter evaluation.",
        "first_author": "Ralston",
        "journal": "Anaesthesia",
        "year": 1991,
        "url": "https://doi.org/10.1111/j.1365-2044.1991.tb09410.x",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      }
    ]
  },
  "evidence_last_evaluated": "Oct 25, 2026",
  "rating_history": [
    {
      "date": "2026-07-21",
      "rating": "Established",
      "from": null,
      "rule_version": "1.4"
    },
    {
      "date": "2026-09-04",
      "rating": "Emerging",
      "from": "Established",
      "rule_version": "1.4"
    },
    {
      "date": "2026-09-17",
      "rating": "Uncertain",
      "from": "Emerging",
      "rule_version": "1.4"
    }
  ],
  "versions": [
    {
      "version": "1.0",
      "date": "2026-10-24",
      "rating": "Uncertain",
      "change": "First published."
    },
    {
      "version": "1.1",
      "date": "2026-10-25",
      "rating": "Uncertain",
      "change": "Corrected a limitation: one cited Apple Watch study did test skin tone, against a fingertip oximeter rather than arterial blood."
    }
  ],
  "research_desk": "https://knowyourprime.com/research-desk-spo2#measurement_validity",
  "related_findings": [
    "https://knowyourprime.com/evidence-pulse-oximeter-skin-tone-bias"
  ],
  "related_articles": [
    "https://knowyourprime.com/how-accurate-is-apple-watchs-blood-oxygen-reading",
    "https://knowyourprime.com/whats-the-difference-between-sao2-and-spo2",
    "https://knowyourprime.com/wearable-blood-oxygen-vs-finger-pulse-oximeter-accuracy",
    "https://knowyourprime.com/wearable-spo2-accuracy-at-altitude"
  ],
  "methodology": "https://knowyourprime.com/methodology",
  "citation": "KnowYourPrime Evidence Registry, Finding KYP-ER-0001, version 1.1, reviewed 2026-10-25. https://knowyourprime.com/evidence-wearable-blood-oxygen-accuracy"
}