Do Cold Hands or Poor Circulation Throw Off Blood Oxygen Readings?
Most oximeter models stayed accurate in poorly perfused adults. In one 146-person study, low blood flow plus dark skin gave the largest missed readings.
Evidence rating for the proposition “Pulse oximeter measurement bias varies systematically with skin pigmentation”: Uncertain · KnowYourPrime Evidence Registry, Finding KYP-ER-0002
Most oximeters stay accurate with poor circulation, but not for everyone. A review of 22 studies found 75% of oximeter models accurate in adults with poor circulation. Newer models and earlobe placement did better. In a 146-person study of two clinical finger oximeters, missed low oxygen under low blood flow was 1.1% in light skin, 8.2% in medium skin and 21.1% in dark skin, and errors read high. No source here tested a consumer wrist wearable under controlled poor circulation.
Do oximeters stay accurate when circulation is poor?
Most did. A 2022 systematic review covered 22 studies of adults with conditions that cause poor peripheral perfusion. These included hypothermia, hypotension, hypovolemia and vasoconstricting drugs, plus experimental conditions. Arterial blood gas readings were the comparison.
Seventy-five percent of oximeter models were accurate in poorly perfused patients. Modern oximeters with more complex algorithms were more likely to be accurate than older models. Earlobe placement seemed more accurate than the fingertip.
The review flags gaps. Only one study controlled for skin pigmentation. None strictly followed FDA recommendations for oximeter accuracy experiments.
1 study
- In 22 studies of adults with poor peripheral perfusion, 75% of oximeter models were deemed accurate. Modern oximeters using more complex algorithms were more likely to be accurate, earlobe placement seemed more accurate than fingertip, and only one study controlled for skin pigmentation.
Which way does poor circulation push the reading?
Reviews say low, and one trial found high. A 2024 review of 23 studies concluded low perfusion, cold skin, nail polish or tattoos, anemia and altitude training may lead to underestimation of oxygen saturation. Increased skin pigmentation, hemoglobinopathies and high skin temperature may lead to overestimation.
The review notes variability and heterogeneity across the studies. It says these limit the consistency and precision of the evidence.
The directions can interact. A prospective study found that in lightly pigmented people only low perfusion was linked to high-reading bias. In medium and dark skin, bias increased with both low perfusion and the degree of low oxygen.
Does skin tone change what poor circulation does to a reading?
In this study, yes. The Nellcor N-595 and Masimo Radical 7 were tested in 146 healthy people: 25 with light skin, 78 with medium and 43 with dark. Researchers analyzed 9,763 matched readings during stable low oxygen, with arterial saturation from 68% to 100%.
Skin pigment, perfusion index and the degree of low oxygen all contributed to error in both devices. Sex and age did not.
A missed diagnosis of hypoxemia meant a reading of 92% to 96% when true saturation was under 88%. Under low perfusion, this happened 1.1% of the time in light skin, 8.2% in medium skin and 21.1% in dark skin. The authors conclude that low perfusion plus darker skin leads to clinically significant high-reading errors.
An earlier study of 21 people found finger oximeters overestimated saturation by 3.56% at 60 to 70% in dark skin against 0.37% in light skin. Bias grew roughly in proportion to desaturation.
2 studies
- In 146 healthy people using the Nellcor N-595 and Masimo Radical 7, missed diagnosis of hypoxemia under low perfusion was 1.1% in light skin, 8.2% in medium skin and 21.1% in dark skin. Skin pigment, perfusion index and degree of low oxygen all contributed to error.
- In 11 people with dark skin and 10 with light skin, three finger oximeters overestimated saturation by 3.56% at 60 to 70% in dark skin against 0.37% in light skin.
What about motion and older models?
Both matter. In a 2002 laboratory test, 20 oximeters were studied during hand motion and low oxygen. The share of time the reading stayed within 7% of control was 94% for the Masimo SET, 69% for the Nellcor N-395 and 28% for the older Criticare 5040.
That study predates today's algorithms. It shows why model and signal processing count. See whether a wearable's blood oxygen reading works the same for everyone, how wearables measure blood oxygen and wrist versus finger accuracy.
What does this not settle?
None of these sources tests a consumer wrist wearable under controlled poor circulation. The main studies used clinical finger oximeters in healthy volunteers or adults with specific conditions.
The review found the evidence on skin pigmentation was thin. The two directions of bias, low from poor circulation and high from darker skin, have not been sorted out for wearables.
The skin tone and perfusion figures come from clinical finger oximeters in 146 healthy volunteers, and the review found only one poor-perfusion study that controlled for skin pigmentation. None tested a consumer wrist wearable, cold hands in everyday use, or people with circulation disease wearing one.
Common questions
Does poor circulation make pulse oximeters inaccurate?
Mostly not. In a review of 22 studies, 75% of oximeter models were accurate in adults with poor perfusion, and newer models did better.
Does skin tone change the effect of poor circulation?
In a 146-person study, missed hypoxemia under low perfusion was 1.1% in light skin, 8.2% in medium skin and 21.1% in dark skin, with high-reading errors.
Does poor circulation make a reading too low or too high?
A 2024 review said low perfusion and cold skin may underestimate saturation, while darker skin may overestimate it. A prospective study found high-reading bias with low perfusion, especially in medium and dark skin.
Is the earlobe more accurate than the finger?
Earlobe placement seemed more accurate than fingertip in poorly perfused adults in a review of 22 studies.
Has a smartwatch been tested under poor circulation?
Not in the sources reviewed here, which used clinical finger oximeters.
KnowYourPrime Evidence Registry: Finding KYP-ER-0019: Blood Oxygen Readings With Poor Circulation · Finding KYP-ER-0001: Smartwatch Blood Oxygen (SpO2) Accuracy Against Arterial Blood (SaO2)
Sources
- Accuracy of pulse oximeters in measuring oxygen saturation in patients with poor peripheral perfusion: a systematic review. [funding listed from a ResMed-endowed research chair]
- Determining factors of pulse oximetry accuracy: a literature review.
- Low Perfusion and Missed Diagnosis of Hypoxemia by Pulse Oximetry in Darkly Pigmented Skin: A Prospective Study.
- Effects of skin pigmentation on pulse oximeter accuracy at low saturation.
- "Motion-resistant" pulse oximetry: a comparison of new and old models.