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What is a CGM? Flash glucose monitoring and CGM.

There’s been a lot of talk lately about CGM because of the #cgm4all campaign. But what exactly is a CGM? What is flash glucose monitoring? And how do you decide what’s best for you? Here’s all you need to know to make an informed decision.

What is a CGM? Continuous Glucose Monitoring

A CGM is a Continuous Glucose Monitor: a sensor that is inserted into your body (usually your stomach, upper arm or thigh) that takes constant blood sugar readings throughout the day. When the sensor is inserted, there’s a needle to open the skin, and then a tiny filament is left behind. This filament takes glucose readings in the interstitial fluid (the fluid surrounding the cells) all day and night – 24 hours a day. 

These readings are sent to a reader, usually an app on your smartphone. This means you can see what your blood sugar is doing every hour of the day. Most CGMs also come with high and low alerts, so they will sound an alarm if your blood sugar is above or below your target range. Because the readings are coming from the interstitial fluid and not the blood, they are generally around 10 minutes ‘behind’ a fingerstick blood glucose test.

CGMs need to be ‘calibrated’ every day – which means you take a normal fingerstick blood glucose test and compare it to the number the CGM is giving you, and input any differences.

There are two CGMs available in South Africa: the Dexcom and the Medtronic Guardian Connect.  

what is a cgm

All about flash glucose monitoring

At the moment there is only one flash glucose monitor on the market – the Abbott FreeStyle Libre. This system also has a small sensor that is inserted into the back of the arm (the size of a R5 coin) and you get your readings by scanning this sensor with a reader or an app installed on your compatible smartphone. 

You don’t need to calibrate your FreeStyle Libre with fingerstick blood tests, but if the reading you are given doesn’t match how you feel (if you feel your blood sugar is going low, but it says you’re fine) then the user’s guide suggests testing with a blood glucose monitor to be sure.

The biggest differences between CGM and flash glucose monitors are price and alarms. You don’t get alarms with a flash glucose monitor (because you have to scan the sensor to get readings, they aren’t automatically sent to your reader). Your doctor will advise you what is best for you – alarms can be necessary for those who are hypo unaware (who can’t feel low blood sugar) or for children. 

Price is the other big difference – the FreeStyle Libre system in South Africa is significantly cheaper than any other CGMS on the market. It costs R1980 for a month (two sensors of 14 days each). You can read our FAQ about the FreeStyle Libre system here

Why it’s so helpful

Both CGMs and flash glucose monitors are enormously helpful. Life-changing, even. Instead of just 4 or 5 readings at points during the day, you get to see a wealth of data to understand your diabetes. You can see at a glance what your blood sugar is doing now, and where it’s going. Trend arrows are probably the most powerful part of this tech, as they tell you not only what your blood sugar is doing right now, but if it’s going up or down. And if it’s going up or down, is it a gradual increase or decrease, or an urgent one? It is much easier to avoid high highs and low lows with this information.

Trends and reports

The other kind of data available to you is trend graphs (so you can see if you tend to go high or low at a certain time of day), time in target percentage (so you know how much of every day you’re spending in your target range) and average blood glucose. Because all the data is online, it’s also much easier to share with your doctor remotely. This is particularly helpful during COVID-19, as you want to avoid doctors offices and hospitals as much as possible. 

Of course, there are plenty of long-term benefits to using a CGM or flash glucose monitor, too. Numerous studies have shown that this diabetes tech can improve HbA1c, reduce time spent in hypoglycemia (low blood sugar) and increase time spent in a normal blood sugar range. Read the studies here, here and here.

You can also easily track your insulin doses, carbs and exercise so it acts as a diet diary and a reminder of what time you took your insulin. This is invaluable because it can let you know if you need to wait a while before giving a correction dose (if you’re going high) or whether you need to react immediately. 

How to decide what’s right for you

If you are ready to take control of your diabetes, a CGM or flash glucose monitor can be life-changing. The information it offers is a full picture of how your blood sugar behaves all day and night. This can empower you to make the right decisions regarding food and exercise, discuss your diabetes treatment plan with your doctor and if you need to change your insulin dosage, and help you spend more of your time in your target range.

The choice of which CGM or flash glucose monitor is right for you is a personal one – and one that you need to discuss with your doctor. Many prefer the FreeStyle Libre because it is smaller and slimmer than other CGM options. The price is also a big decision factor. Others would prefer to pay more for the alarms – especially parents of Type 1 diabetic children, or those who suffer from night hypoglycemia and need to be woken up by an alarm if their blood sugar goes too low. And there are those who don’t want to do any fingerstick blood tests, so they prefer the option of a flash glucose monitor that doesn’t need to be calibrated.

You can always test out the various systems and discuss what works for you with your doctor.

How to get a CGM / flash glucose monitor


The #cgm4all campaign has highlighted the need for medical aids to listen to Type 1 diabetics, and so many people with diabetes have spoken up in support of it – check out all the videos and posts here. We will hopefully be reporting on the good news that medical aids support diabetes tech for people living with Type 1 diabetes in the near future! In the meantime, you can appeal to your medical aid to cover your CGM or flash glucose monitor.

Abbott (who manufactures the FreeStyle Libre system) have a free patient support programme that helps you to apply to your medical aid to get it covered.
Simply email abbottdiabetescaresa@supportwindow.co.za or call 010 786 0316 to get started.

If you’re ready to get a CGM or flash glucose monitor, here’s how you do it:

Dexcom: Fill out this form and a Dexcom representative will call you.

Medtronic Guardian Connect: Call 0800 MED PUMP (633 7867) to get started.

Abbott FreeStyle Libre: Sensors are available online from the CDE Online Store (free shipping when you order two or more sensors) or Pharmacy Direct, a courier pharmacy that delivers anywhere in South Africa. You can also buy it in person at the CDE Pharmacy in Houghton, Johannesburg, or from M-Kem in Durbanville, Cape Town.

Any more questions about CGMs or flash glucose monitors?

We hope this has answered all your questions about how CGMs and flash glucose monitors work. If you still have questions, ask us below and we’ll find the answers! 

ADC-25467 v1 Aug 2020

Published inCommunityResearch

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