--- title: "Blood Oxygen Readings With Poor Circulation | KnowYourPrime Evidence Registry" description: "Finding KYP-ER-0019, rated Uncertain. On its own, poor circulation is handled reasonably well by modern clinical oximeters, but combined with darker skin the readings miss low oxygen far more often: in a laboratory study of 146 people under low perfusion, low oxygen went undetected in 21.1..." url: https://knowyourprime.com/evidence-blood-oxygen-poor-circulation --- KnowYourPrime Evidence Registry · Finding KYP-ER-0019 # Blood Oxygen Readings With Poor Circulation Question assessedDoes poor circulation make a pulse oximeter or smartwatch blood oxygen reading unreliable? KnowYourPrime evidence rating Uncertain Evidence is conflicting, inconsistent, or difficult to interpret. On its own, poor circulation is handled reasonably well by modern clinical oximeters, but combined with darker skin the readings miss low oxygen far more often: in a laboratory study of 146 people under low perfusion, low oxygen went undetected in 21.1 percent of readings with dark skin against 1.1 percent with light skin. Finding KYP-ER-0019 Version 1.2 Reviewed October 24, 2026 Rating rule 1.6 [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/) ## Why this is rated Uncertain A systematic review of patients with poor perfusion found oximeters accurate, especially newer models and earlobe sensors, which is the clean anchor. It also noted that only one of its studies controlled for skin pigmentation. A prospective study built to fill that gap contradicts the claim on its core: low perfusion and darker skin together produced clinically significant high readings. With both present, the rule rates the claim Uncertain. How the rating rule reads this evidence - Systematic-review or meta-analytic evidence affirms the core relationship. - Multiple supporting studies are consistent with the core relationship. - The claim rests on a single anchor whose finding affirms it; a second independent affirming anchor is needed to reach Established. - 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. ## Key results - A systematic review of 22 studies in adults with poor peripheral perfusion, each compared with arterial blood gas, concluded oximeters were accurate, particularly newer models and earlobe placement. (Poorzargar et al., Journal of Clinical Monitoring and Computing, 2022) - In 146 healthy subjects stratified by skin type, missed hypoxemia under low perfusion occurred 1.1 percent of the time for light skin, 8.2 percent for medium and 21.1 percent for dark. (Gudelunas et al., Anesthesia and Analgesia, 2024) - In 46 critically ill patients over 48 hours, oximetry bias against co-oximetry was -2.29 percent, and with abnormal cardiac index the oximeter overestimated saturation by up to 7 points. (Smatlak et al., American Journal of Critical Care, 1998) ## What this finding covers **Applies to:** Clinical pulse oximeters in adults with poor peripheral circulation, compared with arterial blood. **Does not cover:** Direct tests of consumer smartwatches with poor circulation, which are scarce; cold hands during everyday use, except as a cause manufacturers name; children. ## Limitations - Most evidence is from hospital and laboratory oximeters, not wrist wearables. - Perfusion was defined and measured differently across studies. ## Evidence base 7 studies scored · 1 anchor · 3 conflicting · 3 supporting · Evidence last evaluated Oct 25, 2026 ### Anchor studies The studies the rating rests on. 1. Accuracy of pulse oximeters in measuring oxygen saturation in patients with poor peripheral perfusion: a systematic review.Poorzargar et al., Journal of Clinical Monitoring and Computing, 2022. [doi.org/10.1007/s10877-021-00797-8](https://doi.org/10.1007/s10877-021-00797-8) \[funding listed from a ResMed-endowed research chair\] ### Conflicting studies Studies whose findings run against the claim. 1. Low Perfusion and Missed Diagnosis of Hypoxemia by Pulse Oximetry in Darkly Pigmented Skin: A Prospective Study.Gudelunas et al., Anesthesia and Analgesia, 2024. [doi.org/10.1213/ANE.0000000000006755](https://doi.org/10.1213/ANE.0000000000006755) 2. Pulse oximetry: principles and limitations.Sinex et al., The American Journal of Emergency Medicine, 1999. [doi.org/10.1016/s0735-6757(99)90019-0](https://doi.org/10.1016/s0735-6757(99)90019-0) 3. Clinical evaluation of noninvasive monitoring of oxygen saturation in critically ill patients.Smatlak et al., American Journal of Critical Care, 1998. [pubmed.ncbi.nlm.nih.gov/9740887/](https://pubmed.ncbi.nlm.nih.gov/9740887/) ### Supporting studies Studies consistent with the claim that do not carry the rating on their own. 1. Determining factors of pulse oximetry accuracy: a literature review.León-Valladares et al., Revista Clinica Espanola, 2024. [doi.org/10.1016/j.rceng.2024.04.005](https://doi.org/10.1016/j.rceng.2024.04.005) 2. Accuracy of pulse oximetry in the intensive care unit.Louw et al., Intensive Care Medicine, 2002. [doi.org/10.1007/s001340101064](https://doi.org/10.1007/s001340101064) 3. Pulse oximetry and postoperative hypothermia. An evaluation of the Nellcor N-100 in a cardiac surgical intensive care unit.Gabrielczyk et al., Anaesthesia, 1988. [doi.org/10.1111/j.1365-2044.1988.tb09025.x](https://doi.org/10.1111/j.1365-2044.1988.tb09025.x) ## Version history | Version | Date | Rating | Change | | --- | --- | --- | --- | | 1.0 | October 24, 2026 | Uncertain | First published. | | 1.1 | October 24, 2026 | Uncertain | Opening restated in plain words; the size of the skin-tone difference stays in the key results with its study context. | | 1.2 | October 24, 2026 | Uncertain | Opening restores the skin-tone figures with their study and sample, under the revised opening rule. | Rating history on the research desk: Uncertain (September 29, 2026). ## Cite this finding KnowYourPrime Evidence Registry, Finding KYP-ER-0019, version 1.2, reviewed 2026-10-24. https://knowyourprime.com/evidence-blood-oxygen-poor-circulation Machine-readable: [JSON](https://knowyourprime.com/evidence-blood-oxygen-poor-circulation.json) · [Markdown](https://knowyourprime.com/evidence-blood-oxygen-poor-circulation.md) · [All findings](https://knowyourprime.com/evidence) ## Related - Research desk: [the blood oxygen research desk entry for this question](https://knowyourprime.com/research-desk-spo2#poor_perfusion), with every scored study and its role - Related finding: [Pulse Oximeter Accuracy and Skin Tone](https://knowyourprime.com/evidence-pulse-oximeter-skin-tone-bias) (KYP-ER-0002) - Related finding: [Smartwatch Blood Oxygen (SpO2) Accuracy Against Arterial Blood (SaO2)](https://knowyourprime.com/evidence-wearable-blood-oxygen-accuracy) (KYP-ER-0001) - On this site: [Do Cold Hands or Poor Circulation Throw Off Blood Oxygen Readings?](https://knowyourprime.com/does-poor-circulation-affect-blood-oxygen-sensor-accuracy) - On this site: [Does Wearable SpO2 Work the Same for Everyone?](https://knowyourprime.com/does-your-wearables-blood-oxygen-reading-work-the-same-for-everyone) This is KnowYourPrime's own assessment of the published evidence, rated under the [KnowYourPrime evidence methodology](https://knowyourprime.com/methodology). The rating is set by a fixed rule from the roles of the studies above and moves only when the evidence or the rule changes. Every change to the rating or the text is published as a new dated version. To report an error, write to [corrections@knowyourprime.com](mailto:corrections@knowyourprime.com). ```json { "@context": "https://schema.org", "@type": "Article", "@id": "https://knowyourprime.com/evidence-blood-oxygen-poor-circulation#finding", "headline": "Blood Oxygen Readings With Poor Circulation", "name": "KnowYourPrime Evidence Registry, Finding KYP-ER-0019: Blood Oxygen Readings With Poor Circulation", "license": "https://creativecommons.org/licenses/by/4.0/", "description": "On its own, poor circulation is handled reasonably well by modern clinical oximeters, but combined with darker skin the readings miss low oxygen far more often: in a laboratory study of 146 people under low perfusion, low oxygen went undetected in 21.1 percent of readings with dark skin against 1.1 percent with light skin.", "url": "https://knowyourprime.com/evidence-blood-oxygen-poor-circulation", "identifier": { "@type": "PropertyValue", "propertyID": "KnowYourPrime Evidence Registry finding ID", "value": "KYP-ER-0019" }, "version": "1.2", "datePublished": "2026-10-24", "dateModified": "2026-10-28", "inLanguage": "en", "isPartOf": { "@type": "CreativeWorkSeries", "name": "KnowYourPrime Evidence Registry", "url": "https://knowyourprime.com/evidence" }, "author": { "@type": "Organization", "name": "KnowYourPrime", "url": "https://knowyourprime.com" }, "publisher": { "@type": "Organization", "@id": "https://knowyourprime.com/#organization", "name": "KnowYourPrime", "url": "https://knowyourprime.com" }, "about": "Does poor circulation make a pulse oximeter or smartwatch blood oxygen reading unreliable?", "citation": [ { "@type": "ScholarlyArticle", "name": "Accuracy of pulse oximeters in measuring oxygen saturation in patients with poor peripheral perfusion: a systematic review.", "url": "https://doi.org/10.1007/s10877-021-00797-8", "datePublished": "2022", "isPartOf": { "@type": "Periodical", "name": "Journal of Clinical Monitoring and Computing" } }, { "@type": "ScholarlyArticle", "name": "Low Perfusion and Missed Diagnosis of Hypoxemia by Pulse Oximetry in Darkly Pigmented Skin: A Prospective Study.", "url": "https://doi.org/10.1213/ANE.0000000000006755", "datePublished": "2024", "isPartOf": { "@type": "Periodical", "name": "Anesthesia and Analgesia" } }, { "@type": "ScholarlyArticle", "name": "Pulse oximetry: principles and limitations.", "url": "https://doi.org/10.1016/s0735-6757(99)90019-0", "datePublished": "1999", "isPartOf": { "@type": "Periodical", "name": "The American Journal of Emergency Medicine" } }, { "@type": "ScholarlyArticle", "name": "Clinical evaluation of noninvasive monitoring of oxygen saturation in critically ill patients.", "url": "https://pubmed.ncbi.nlm.nih.gov/9740887/", "datePublished": "1998", "isPartOf": { "@type": "Periodical", "name": "American Journal of Critical Care" } }, { "@type": "ScholarlyArticle", "name": "Determining factors of pulse oximetry accuracy: a literature review.", "url": "https://doi.org/10.1016/j.rceng.2024.04.005", "datePublished": "2024", "isPartOf": { "@type": "Periodical", "name": "Revista Clinica Espanola" } }, { "@type": "ScholarlyArticle", "name": "Accuracy of pulse oximetry in the intensive care unit.", "url": "https://doi.org/10.1007/s001340101064", "datePublished": "2002", "isPartOf": { "@type": "Periodical", "name": "Intensive Care Medicine" } }, { "@type": "ScholarlyArticle", "name": "Pulse oximetry and postoperative hypothermia. 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