Pulse Oximeters: False Readings Explained

Amid this COVID-19 pandemic, pulse oximeters have become an increasingly common piece of monitoring equipment in most households and clinical settings. People are now more careful and concerned about taking proper safety precautions.

A pulse oximeter is a small, lightweight, and portable device that quickly and easily evaluates the oxygen levels from our fingertips.

Until the COVID-19 pandemic, there wasn’t much awareness about this product. But today, its popularity has surged. However, due to a lack of adequate knowledge of the functioning of the product, there are several misconceptions and confusion around false readings.

So to clear all your misconceptions, please read below. This may involve some technical details, so please read carefully.

Why would a pulse oximeter give a reading when used with a pen or a pencil?

The patient’s condition is detected based on the sensitivity of the amount of red and infrared light falling on the sensor of the pulse oximeter or probe in other machines. When this is obstructed by increasing the distance between the LED and the detector, or by inserting some object inside the probe, the module will think the finger is inserted and will start searching for a pulse. In this condition, the varying intensity of diffused light falling on the detector can cause a pulsating effect and lead to a reading on the pulse oximeter. The pulse oximeter is a very sensitive device. However, if the gap between the LED and the sensor is closed fully, so that no light falls on the detector, the pulse oximeter will sense no pulse and there won’t be any reading.

Pulse oximeter calculating process

Small beams of light pass through the blood in the finger, measuring the amount of oxygen. It does this by measuring changes in light absorption in oxygenated or deoxygenated blood. The pulse oximeter will thus be able to tell you your oxygen saturation levels. The same is observed in all other devices.

How Accurate Are Readings of a Pulse Oximeter

A good Pulse Oximeter displays SpO2 recordings along with a graph. A Pulse Oximeter that comes with a PI indication comes in handy for the physician to better assess your condition. BPL pulse oximeters have an accuracy of ±2, which means that the readings are quite accurate. You should consult a medical professional to give you a better idea of how to read a pulse oximeter for your needs. 

Why the Readings of a Pulse Oximeter Fluctuates  

There are several instances where you might find your pulse oximeter showing irregular readings. This can be due to various factors. Some of them are mentioned below. 

1- Nail Polish

2- Cold Hands

3- Injury on the finger


We strongly suggest you to not insert any objects like a pencil, pen, etc in the pulse oximeter to check the readings. This may damage the sensor of the device and can lead to malfunctioning. 

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