Coping with CGM challenges

Woman using Freestyle Libre glucose monitor

 While there are many benefits to continuous glucose monitoring, including having access to 24/7 readings and trend arrows, the reduced need for fingerprick glucose checks and alerts to inform the wearer of out-of-target readings, the devices aren’t without their problems. 

In this post I discuss some of the challenges of CGM along with tips for navigating these challenges.

With recent changes to the Australian Government access to subsidised continuous and flash glucose monitoring through the NDSS, an increasing number of Australians with diabetes are now using continuous glucose monitoring (CGM) devices.

While there are many benefits to this technology, including having access to 24/7 readings and trend arrows, the reduced need for fingerprick glucose checks and alerts to inform the wearer of out-of-target readings, the devices aren’t without their problems.  In this post I discuss some of the challenges of CGM along with tips for navigating these challenges.


It can be frustrating when your CGM device and blood glucose meter show quite different readings. There are a few reasons this might happen, but the main one is what’s called lag time. CGM devices measure glucose levels in the interstitial fluid (the fluid between your cells) rather than the blood.

Glucose travels to the blood first and then to the interstitial fluid, which means that CGM and blood glucose levels normally won’t be exactly the same. When glucose levels are stable, the readings should be close, but there will be a greater difference when your levels are rising or falling quickly. When rising quickly, your blood glucose reading will likely be higher than the CGM. When dropping quickly, your blood glucose reading will probably be lower than the CGM.

For devices that need calibrating, the accuracy also depends on calibrating correctly. This means following the directions from your device manufacturer as to when and how often to calibrate (each device is different), using the same blood glucose meter for all calibrations, washing your hands before doing a calibration finger prick reading and only calibrating when blood glucose levels are between 2.2 and 22.2mmol/L. The devices can’t be calibrated above or below this range.

Finally, some medications may affect your readings, so it’s important to know if there are any interactions with the device you use. For example, medications containing acetaminophen (paracetamol) can affect the accuracy of some CGM devices (giving falsely high readings for up to 8 hours after taking the medication), while others may be affected by high doses of vitamin C. Speak to your health professionals about which medications can affect your device and suitable alternatives.

If you’ve considered all the factors above but are still having problems with sensor accuracy, speak with your diabetes educator. You can also ring the device manufacturer’s 24/7 helpline and they can troubleshoot any problems with you and may replace the sensor if they determine that it’s faulty.

Information overload

One of the major benefits of CGM is the amount of additional information it provides, from 24/7 readings to trend arrows and statistics. But it can also be overwhelming to see what your glucose levels are doing all the time.

The key is learning how to use and interpret the information provided by your device so you can use it to improve your diabetes management rather than letting it become something else to worry about.  This is where your diabetes educator or diabetes specialist can help. Getting the right training upfront along with ongoing help, can ensure that CGM is something that supports your diabetes management rather than just stressing you out.

Being attached

Wearing the sensor and transmitter 24/7 can take some getting used to and some people find it uncomfortable. Finding a suitable site can be more difficult in young children and adults who are slim, as they don’t have much body fat. If you also use an insulin pump, it means having two different devices attached to your body and rotating where you place them both can be more challenging.

For sensors placed on your tummy, an important consideration is the clothing you usually wear and avoiding placing the sensor at your waistline/beltline where it might rub or be at risk of getting knocked off. Instead, if you wear high waisted pants or skirts you might want to consider placing your sensor on the lower part of your tummy and if you wear low waisted clothing consider placing it above your waistband.

If you are struggling to find a site that works, speak with your diabetes educator who can discuss the options and help you work out the best place to insert your sensors, depending on which device you are using.

Staying attached

While some people find their sensors easily stay in place, others find it hard to keep the sensor and transmitter attached. This can be more of a challenge if you are active, particularly if you sweat a lot during exercise, spend a lot of time in water or play contact sports. It’s also possible to knock the device off while drying yourself after a shower, getting dressed, sleeping or for young children, while playing.

Unfortunately, sensors can’t be reused if they come off, so if you are having ongoing problems with staying attached, it’s worth looking at using extra tape to secure the device. There are many options available and your health professional can provide advice on which tape might be best for you, but some options to check out include Rockadex and Not Just a Patch.

Alert fatigue or distress

The alarms and alerts on CGM devices are one of the major reasons many people choose to start CGM. If you have impaired awareness of hypoglycaemia (meaning you don’t detect the early warning signs) or are a parent of a young child with type 1 diabetes, they can be a lifesaver and provide significant peace of mind. They are also particularly useful for alerting you to overnight hypos, which can be harder to detect.

But when you first get started, or if the device is alarming frequently, you may find the alarms annoying, disruptive or stressful.

Understand that these alerts are designed to help you but if they’re causing distress they can be changed or turned off so you’re only alerted when it’s important to you. The key is setting the right targets for you or your child – something that’s important to discuss with your diabetes educator or doctor when you set up the device.

The low alerts are most important but you might want to set your high alert a bit higher initially, or even turn it off completely, until you get used to the device. Also consider setting alerts so they only sound at times where you would take action to correct high or low glucose levels.  For example, you might want to keep your readings between 4 and 10mmol/L but if you wouldn’t correct a high reading until it reaches 13mmol/L, then consider setting your high alert at this reading.

These settings can be changed at any time, particularly as you become more familiar with CGM.

 CGM doesn’t mean the end of fingerprick checks

Using CGM can certainly reduce the number of fingerprick checks needed to manage your diabetes and this is the major reason many people make the switch.  However, using CGM doesn’t mean doing away with your regular blood glucose meter for good.

Some CGM devices still need calibrating at least twice per day, by entering a fingerprick glucose reading.  And not all devices are currently approved for self-adjustment of insulin doses which means that a finger prick reading is still recommended before making decisions about adjusting insulin doses.

Finally, for all devices, fingerprick checks are still recommended when glucose levels are changing rapidly, to confirm hypoglycemia, before giving a correction dose for high glucose levels, and when symptoms don’t match your CGM reading.

Staying connected and capturing all data 

With real-time CGM devices (such as Dexcom and Medtronic) your phone, pump or receiver needs to be within six metres of your sensor/transmitter. With some devices, the transmitter will hold data for a certain period of time (3 to 10 hours) but after this, there will be a gap in your data until you come back in range. With other devices there will be a gap for the entire time the receiver and sensor/transmitter are out of range.

For flash glucose monitors (Freestyle Libre) the sensor stores 8 hours of data, so you need to ‘scan’ your sensor with your phone or reader at least every 8 hours to avoid a gap in data.  This means remembering to scan just before you go to sleep and first thing on waking, to see your overnight data, and at least every 8 hours during the day

Finally, remember that just because you’ve started on CGM, it doesn’t mean you are stuck with it.  While you will get the most benefit from CGM if you wear it full-time, that doesn’t mean you (or your child) can’t take a break. If you are feeling overwhelmed by all the data, getting frustrated at the alarms or finding your device uncomfortable to wear, speak to your health professionals about whether having a CGM ‘holiday’ would help or whether they can suggest some other solutions for dealing with these issues.


This article was originally published in Diabetic Living Magazine and has been republished with permission.