Can a mobile phone measure blood oxygen? Is it accurate?

Audit expert: Gu Haitong

Deputy Chief Physician, Department of Respiratory Medicine, Beijing Tongren Hospital, Capital Medical University

During the Spring Festival, many migrant workers return home from all over the country. Under the current situation, people can't help but worry about the health of the elderly at home. Among the various monitoring indicators of physical condition, the blood oxygen index can measure the lung function and circulatory function, which can more intuitively reflect the health status.

When it is not possible to buy a blood oximeter, some people use other electronic devices to measure blood oxygen, including sports bracelets or watches, and mobile phones are also marked with a blood oxygen SPO₂ (transcutaneous blood oxygen saturation) measurement function. But we still have to ask, are their measurement results accurate?

Blood oxygen determination indicators

The full name of "blood oxygen" we usually talk about is blood oxygen saturation. As we all know, the oxygen inhaled by the human body through breathing will dissolve in the blood and combine with hemoglobin, and blood oxygen is the degree of combination of oxygen and hemoglobin, expressed as the percentage of oxygenated hemoglobin in the blood to the total hemoglobin capacity. This indicator can be used as a reference for the health of the human heart and lungs.

Source: Pixabay

What is the normal range of blood oxygen for a person? The human body's blood oxygen index is divided into venous blood oxygen and arterial blood oxygen, and the oximeter monitors arterial blood oxygen. The normal blood oxygen saturation of the human body is about 98% , mostly in the range of 95% to 100%. If the blood oxygen is lower than 95%, then be careful, this is a manifestation of insufficient oxygen supply to the body, which is mild hypoxia.

Blood oxygen saturation is one of the important diagnostic indicators for COVID-19. Several consecutive editions of the "Diagnosis and Treatment Plan for New Coronavirus Pneumonia" have pointed out that when the oxygen saturation under inhaled air conditions (oxygen concentration 21%) is lower than 93%, the patient is seriously ill and needs to seek medical attention as soon as possible for assisted breathing treatment.

Insufficient oxygen supply to the body can easily have a negative impact on important organs such as the heart, lungs, and brain. At this time, oxygen inhalation is needed to increase the oxygen supply. More seriously, if the blood oxygen level is lower than 90%, this is severe hypoxia. At this time, the most important thing is to seek medical attention as soon as possible for emergency treatment.

Source: Sina Finance

The blood oxygen index is a barometer of the human body's physical condition. The testing methods include invasive testing - drawing arterial blood for spectrophotometer testing; and non-invasive testing - using in vitro testing instruments for testing. The latter is the choice of more people for blood oxygen testing.

Common blood oxygen detection instruments include finger clip type, wristband type, palm type and desktop type. Among them, the finger clip type is more popular among families.

Finger Clip Oximeter

Source: Pixabay

The finger clip oximeter only needs to be clipped on the finger, and after clicking the test, the instrument can quickly read the blood oxygen saturation index and pulse rate.

The principle is based on the difference in the absorption spectrum characteristics of hemoglobin and oxygenated hemoglobin in arterial blood in the red and infrared light regions. Lambert-Beer's law is used to establish a data empirical formula, and finally, through the data processing algorithm, accurate sensing is achieved to obtain the blood oxygen reading. The principle is exactly the transmission type shown in the figure below.

The principle of finger clip oximeters is mostly transmission type, while wearable bracelets measure blood oxygen mostly by reflection type.

Source: Salt Finance

How does a mobile phone measure blood oxygen?

Nowadays, people pay much more attention to health monitoring, and many smart wearable bracelets are equipped with blood oxygen measurement function.

Due to the poor light transmittance at the wrist, the detection principle is different from the projection type of the finger clip oximeter, and is mostly reflective, that is, the receiving and transmitting instruments are at the same end. However, compared with the fingertips, the distribution of blood vessels at the wrist is relatively more complicated, making it more difficult to measure blood oxygen, and the accuracy of the test results is somewhat different from that of the finger clip type.

Reflective blood oxygen detection principle diagram

Source: Sohu

Today, when blood oxygen measurement using oximeters and smart bracelets is widely used, a new way to measure blood oxygen has emerged, which is measuring blood oxygen using a mobile phone.

The method of measuring blood oxygen with a mobile phone includes placing a finger in front of the camera and flash, or pointing the mobile phone camera at the face to record a video. It takes a short time and the results can be obtained in about two minutes.

Blood oxygen measurement page of an APP

Source: Sohu

Is it scientific to measure blood oxygen with a mobile phone?

For the first measurement method of pointing the camera at the finger, the mobile phone uses a flash to emit white light, and the camera acts as a sensor to receive the reflected signal of the white light. The blood oxygen saturation is measured by detecting the difference in light reflected by oxygen-saturated hemoglobin.

Although this method is convenient, the blood oxygen test readings may not be accurate due to the different models and parameters of various mobile phone cameras on the market. At the same time, during the measurement process, the mobile phone cannot place the finger in a relatively dark environment like a finger-clip oximeter. Therefore, the blood oxygen measurement of the mobile phone is easily disturbed by the ambient light, resulting in inaccurate readings.

Mobile phone camera to measure blood oxygen

Source | "Smartphone camera oximetry in an induced hypoxemia study"

As for the second method, which measures blood oxygen by taking a video of the face and reading the blood flow information from the pulse fluctuations of the face, this method has greater uncertainty than the first method and is more affected by ambient light. It can be seen from this that the accuracy of blood oxygen measurement by mobile phones is far inferior to that of finger-clip oximeters, and the data can only be used for reference.

Source丨Editor

It is true that there are errors in measuring blood oxygen with mobile phones, but there is no need to stay away from it. The blood oxygen content of a healthy person is above 95%, and it will not be lower than this value under normal circumstances. If the value measured by the mobile phone falls within this range, it can confirm to a certain extent that your physical condition is normal and healthy.

The blood oximeter is a medical device and is approved by the State Food and Drug Administration. Therefore, it is strictly managed and meets medical standards. Other electronic devices that monitor blood oxygen do not meet such standards.

Nowadays, people are increasingly aware of their health protection. In addition to blood oxygen testing, heart rate, pulse and other tests are also very popular. Behind all kinds of tests, maintaining good living habits, eating a healthy diet and avoiding risks as much as possible are the only ways to ensure good health.