Freestyle Libre Inaccurate? Here’s Why and What to Do About It

Posted August 26, 2020 by Michael Chamberlain - See Editorial Guidelines
Freestyle Libre inaccurate

Investing in diabetes equipment takes time and money. So, it can be disappointing to end up with equipment that does not meet up to the amount invested in it.

It’s particularly frustrating when equipment like glucose monitoring systems do not meet your standards, as they could end up providing inaccurate readings.

With many CGM’s potentially presenting inaccurate readings, the Freestyle Libre is one such device. This article will give a clear understanding of what’s making your Freestyle Libre inaccurate, what you might be doing wrong, and how to get accurate readings.

Let’s get you a quick summary answer before we move on to more details.

Freestyle Libre Inaccurate? Inaccuracies in freestyle Libre occur because of two main reasons. Either it does not measure the glucose in the blood, but rather the glucose in the interstitial fluid, or because of user error. There may be some other rare instances that can cause inaccuracies in your Freestyle Libre.

Now that we’ve seen the quick answer, let’s get into some of the reasons why these might be the case and how to deal with them.

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Freestyle Libre Inaccuracies

Freestyle Libre Inaccurate

Before talking about inaccuracies, it’s prudent to state that Freestyle Libre cannot always be 100% accurate. Most of these inaccuracies come in the form of a beginner’s challenges, the time it takes for the body to get used to the device, and the way the sensor works.

However, if you experience continuous inaccuracies with your Freestyle Libre, then we recommended looking to get a replacement.

Remember that the Freestyle Libre is factory calibrated. This means that you cannot calibrate it yourself. So, if you find inaccuracies in the sensor, there’s actually little you can do about it other than getting a replacement.

The reason for most of the inaccuracies in Freestyle Libre stems from the purpose of the equipment itself.

Below are a couple of reasons why the Freestyle Libre can be giving out inaccurate readings. 

Measures Interstitial Fluid, Not Blood Glucose

When you test your blood sugar using a fingerprick and glucometer, you measure the glucose directly in your blood. However, the Freestyle Libre and other CGMs measure glucose in the interstitial fluid, rather than the blood. The interstitial fluid is a layer of fluid that surrounds cells below your skin.

This is also why a fingerprick test in which actual blood is tested is considered more accurate than any other equipment.

So, since the Freestyle Libre measures glucose in the interstitial fluid, the results can never be 100% accurate. This is because the glucose in the interstitial fluid is delayed when compared to the blood.

If you have blood sugar levels rising and falling at a fast speed, then the inaccuracies can be greater. There’s typically a delay of 5-15 minutes between the glucose levels in the blood and the interstitial fluid.

This means that the results from a blood glucose meter are often not instantly the same as the Freestyle Libre. Therefore, some patients may perform fingerprick tests from time to time to ensure their blood sugar levels are stable.

Another possible reason why many find the Freestyle Libre inaccurate is that the older models don’t warn you or have any alarms in case of hypoglycemia or hyperglycemia.

The reason is there’s no automated connection between the sensor and the reader device. The sensor continuously measures glucose levels, keeps track of, and stores data, but only transmits it when the reader scans the sensor.

It is important to note here that the manufacturer of the Freestyle Libre has recently (at the time of writing this) released a new model that has optional glucose alarms.

While these are problems that can occur with the device itself for inaccurate readings, other issues can make the Freestyle Libre inaccurate.

Freestyle Libre Inaccurate

User Errors Producing Inaccurate Readings in Freestyle Libre

Some causes of inaccurate readings come from wrong positioning or insertion angles of the sensor.

Freestyle Libre Inaccurate

When you apply the sensor, a small filament sits just underneath the skin in the subcutaneous layer. If the user inserts the sensor at an odd angle or in a place not approved by the manufacturer, it can cause the filament to bend or become flawed. Inaccurate readings can then occur more often.

The other possible cause comes from how the sensor settles underneath the skin. The filament should not be hitting any blood vessels or extending to the muscles. If this happens, the probability of getting inaccurate readings is greater.

Another potential cause for inaccurate readings comes from how well the filament is sitting in the interstitial fluid. This means that the more the sensor is in touch with the fluid, the more probability for the device to give out accurate readings. 

It is important to remember that everybody’s skin is different and the amount of fat in the recommended place of insertion may be less for some patients.

Therefore, we recommend consulting your doctor for the most accurate advice when it comes to applying your Freestyle Libre to help prevent inaccurate readings.

Device Rejection – Rare Cases

Sometimes, in very rare cases, a person’s body may reject the device for a period, especially during the first few uses. So, keep this in mind, and allow some time for adjustment and check how it is working before coming to any conclusions about inaccurate readings.

Some users have found that applying the sensor but delaying the start of it for 24-48 hours can help with avoiding inaccurate readings.

Individuals that are having problems with device rejection may have skin irritation around the sensor along with red or inflamed skin around the area.

What to Do About Inaccurate Readings 

One of the best and most obvious actions to take is to make sure you are not making the mistakes discussed above. Apart from this, one other factor is to allow the gadget to settle in for 24 hours after installation before activating it.

You could, with a doctor’s advice, also try switching application sites. Ensure you’re adequately hydrated before taking readings and avoid sleeping on the sensor. This will help prevent farther problems with the sensor.

Experiencing inaccurate readings can be dangerous as you may not notice severe high or low blood sugar levels, which can be detrimental to your health. If there is something wrong with the sensor, then you can always call the manufacturer. They will often replace malfunctioning sensors free of charge.


We hope this has given you some confidence in using your Freestyle Libre and helps you troubleshoot any inaccuracies as you get used to using your device.

As always, this article is not intended to be complete medical guidance. We would, of course, always recommend consulting your doctor before taking any drugs you feel may not be suitable or effective.

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