Site pictogram Think & Create

Suspicious Reading in Pulse Oximeter? It’s OK

As the rise of COVID-19 patient in Indonesia is climbing, the need in medical supports increases proportionally. These medical supports include Oxygen Supply, Pulse Oximeter, and supplements to aid home-care treatment since most of the hospitals in Indonesia are occupied. Tips and tricks to survive COVID-19 are also circulated in internet through social media or Whatsapp chat.

Recently, one of the most intriguing messages that I received is about ‘Fake Pulse Oximeter’ Here I show you the picture from the footage of person demonstrating which Pulse Oximeter is ‘Fake’:

According to the footage, the blue pulse oximeter is abnormally reading pencil’s saturation that is supposed to be not the object to be read. The blue pulse oximeter is instantly considered as ‘fake’ product while the white pulse oximeter is the example of good pulse oximeter. This footage affects people’s trust to medical tools they own. Although, it is safe to own better accuracy medical devices, it is also important to know why this error happens and whether we need to worry or not.

As one of my internship project in my University is making pulse oximeter, I feel obliged to explain what I know about pulse oximeter from how it works, how this ‘error’ can happen, and conclude whether you really need new pulse oximeter or not. Especially for people who are not coming from engineering background, I need to rewrite some explanation in my language.

How it Works

Healthy human’s blood in the vein has darker color which indicates the blood contains O2. The pulse Oximeter emits and receives infra red and red light. When the finger is clipped by pulse Oximeter this infra red and red light will pass through the skin and vein and collect the amount of light that is received. If the intensity of the received light is almost equal to the emitted, that means the user has low O2 in their blood and need O2 supply immediately. While if the intensity of the received light is less than the emitted, the person has richer O2 because the color saturation ‘blocked’ the light to pass through.

Image from

How this ‘Error’ can Happen

Pulse Oximeter is a great example of analogue electronic application where the ratio between of light intensity from infra red and red light is equal to the blood color saturation.

Deoxy Hb (Red) and Oxy Hb (Blue) based on ratio of red light and infra red absorbance

Let’s go back to the pulse oximeter that clipped pencil color. As you can see the blue pulse oximeter reads the object to have 98% oxygen saturation. The reason of this nature is of course, the pulse oximeter seeing the red color on the pencil body as healthy human blood. This is not the first time pulse oximeter is considered inaccurate. That’s why reading blood saturation from people who has darker color skin is more difficult for pulse oximeter to perceive the blood saturation.


The abnormality that might happen to the blue pulse oximeter as shown as picture above is the oversensitive reading to non-human object. For more accurate reading, it is best to have pulse oximeter that is supported with threshold for more sensitive reading. I believe, medical departments are required to have accurate pulse oximeter. However, for first-aid-kit home care, this blue pulse oximeter still can be used for reading oxygen saturation. Probably, this pulse oximeter is not ideal for measuring person with darker skin. This blue pulse oximeter is suitable for inexpensive and emergency need only. My only advice when you are using blue pulse oximeter, make sure you have clean fingers and no clothing covering the fingers while measuring your Oxygen Saturation.

I hope this helps you to prioritize what you need to improve for COVID-19 first-aid home care. My explanation is supported by some images from howequipmentworks. All explanation is originally written by me, for more detail you can also read it in howequipmentworks. For more question, feel free to contact me through email.

Featured images from:

Mobiele versie afsluiten