Limitations of pulse oximeters and the effect of skin pigmentation

COVID-19 has caused an increase in pulse oximeters being used to help estimate blood oxygen levels and therefore assist in monitoring a person with COVID-19 infection. Recent reports have highlighted that multiple factors, including skin pigmentation, can impact the accuracy of pulse oximeters. Overreliance on pulse oximeters could lead to suboptimal management of patients whose oxygen levels are below normal. This risk is higher in persons with darker skin.

What pulse oximeters are and how they work

A pulse oximeter is a device that is used to estimate the oxygen saturation of the blood. The device is usually placed on a fingertip. It displays values as a percentage, usually 95-100% for healthy individuals, alongside the pulse rate. These devices work by shining light through the skin. The oxygen transporters in blood reflect light differently depending on how much oxygen they contain.

Concerns about accuracy

Pulse oximeters may over or under-estimate oxygen saturation. The accuracy of the measurement has been long known to be affected by many factors, including skin pigmentation. Other factors include correct fitting of the device, peripheral blood flow, nail coatings, tattoos and dyes, and maintenance and cleaning of devices.

Some studies have shown pulse oximeters may over-estimate oxygen saturation levels in people with darker skin pigmentation, which means low oxygen levels (hypoxia) could go unrecognised and untreated (Sjoding et al, Bickler et al). These inaccuracies are greater at lower levels of oxygenation. However, they also occur at saturation levels where key decisions are often made around supplemental oxygen and hospital admission (SaO2 88-94%), with measures that are 3-4 percentage points above the actual oxygen saturation (as determined by gold-standard arterial blood gases) more frequently reported in darker skinned persons. The effect in persons with intermediate skin tones may be in between that of darker and fairer skin tones. The extent of potential inaccuracies varies between devices, but there is insufficient available evidence for the TGA to make recommendations about specific devices.

Home use of pulse oximeters

Pulse oximeters are commonly used in the healthcare setting by clinicians. During COVID-19 there has been increasing home use of these devices by people at home, to assess how the infection is affecting them and to determine if medical intervention is required. Home use of pulse oximeters is safer and more effective when done as part of medical management, overseen by a doctor who will consider other factors when recommending treatment, and may be able to recommend a particular pulse oximeter for use.

Advice for healthcare professionals

Clinicians are reminded that pulse oximeter devices may not accurately detect hypoxaemia. Recent evidence increases concerns that oxygen saturations may more frequently be overestimated by these devices in persons with darker skin (Valbuena). Refer to the device labelling and instructions for use, or the manufacturer's website, to understand the accuracy of a particular pulse oximeter and sensor. Different pulse oximeters and sensors (finger clip versus adhesive) may have different accuracy levels. For example, a pulse oximeter saturation reading of 90% may represent a true arterial blood saturation of 86-94%.

Consider accuracy limitations when using the pulse oximeter to assist in diagnosis and treatment decisions and when developing and utilising clinical guidelines and protocols. Interpret pulse oximeter readings within the context of a patient's entire clinical presentation and incorporate other clinical information into decision-making. Use serial readings and note trends. Recognise that the systems-level risk associated with this issue has increased because of the respiratory pandemic and increased reliance on home-based management.

Advice for patients and consumers

Consumers are reminded that pulse oximeters should not be used in isolation as an indicator of the severity of a patient's illness. The patient's complete clinical presentation must be taken into consideration when making decisions about clinical care. Consumers are also reminded to always follow the instructions for use provided with the device to ensure appropriate use. Factors such as long fingernails, artificial fingernails, nail polish and darker skin pigmentation can result in these types of devices providing inaccurate results.

The TGA recommends that home use of pulse oximeters is safest and most effective when done as part of treatment provided by a Doctor. It is important to learn how to take an accurate measurement, through following the instructions for use and being guided by health professionals. Remember that not all pulse oximeters are of the same quality and accuracy. One US study showed that some cheaper devices without regulatory approval sold to consumers were significantly less accurate than approved devices used in healthcare settings. (Lipnick et al)

Statements from other jurisdictions

The regulatory agencies in the US and UK have also made similar statements regarding pulse oximeters:

• FDA (https://www.fda.gov/medical-devices/safety-communications/pulse-oximeter-accuracy-and-limitations-fda-safety-communication)
• MHRA (https://www.gov.uk/guidance/the-use-and-regulation-of-pulse-oximeters-information-for-healthcare-professionals)

Further actions

The TGA will communicate with clinicians and industry to determine what other actions could help address the risks associated with this issue.

Reporting problems

Consumers and health professionals are encouraged to report problems with medical devices. Your report will contribute to the TGA's monitoring of these products. For more information, see the TGA Incident Reporting and Investigation Scheme (IRIS) or contact the TGA's Devices Post Market Monitoring Section on 1800 809 361.

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For correspondence or further information about Medical Devices Safety Update, contact the TGA's Medical Devices Branch at iris@tga.gov.au or 1800 809 361.