CGM, continuous glucose monitoring, has been around for about a decade, but has only really started making it into the mainstream diabetes community in the last few years.  They work by putting a small sensor under the skin that measures the glucose levels in the interstitial fluid. A reading is taken about every 5 minutes and displayed either on a dedicated receiver, a smart phone or an insulin pump as a number as well as a line graph.

It’s important to know that CGM’s do not measure the glucose levels in the blood, but in the interstitial fluid which is the next location in the glucose chain. The common wisdom is therefore that CGM readings are between 5 and 15 minutes delayed from finger prick blood readings. This isn’t actually quite accurate, but it’s a reasonable enough assumption to start off with.

There are three big brands available on the market – the Freestyle Libre from Abbot, Guardian and Enlite from Medtronic and the G4 and G5 from Dexcom. Each of the systems has it’s own advantages and disadvantages.

Free Style Libre

The Libre is the simplest and the cheapest at just over £50 a sensor that lasts for two weeks and £60 for a reader. It’s small, last two weeks and widely available, but you have to manually scan the sensor to get a reading, it doesn’t have alarms and you can’t calibrate it. This is generally fine for the day time, but it unless someone is awake to scan, less helpful for night time hypoglycemia detection. We’ve tried the Libre, but as our main focus is preventing Cass’ serious night time lows, we didn’t find a sustainable solution for us.

Medtronic’s Guardian and Enlite Sensor System

The Guardian and Enlite work in conjunction with some specific Medtronic pumps but need around £400 of setup for a transmitter and inserter and then cost around £55 for a sensor that lasts six days.  The Medtronic systems are highly accurate, can be calibrated, have customizable alarms and can switch off your insulin to prevent lows, but they are only available if you have the correct pump, only last six days and Medtronic have had some supply problems and are not currently accepting new patients in the UK.

We’ve used the Medtronic Enlite sensors with a 640g Pump for 6 months and found them accurate and useful, but not without issues. We do appreciate the customizable alarms and the ability to suspend insulin delivery as it can prevent hypoglycemia and we’ve avoided severe lows for these six months due to the alert and automatic insulin suspension.

Dexcom’s G4 and G5

The G4 costs £350 for a rechargeable receiver, £260 for a transmitter that lasts around six months and then £51 for a sensor that lasts between 7 and 12 days. The G5 uses your phone as a receiver and the transmitter costs £200 with the sensors costing £51 and they last for 7 – 12 days as well. The Dexcom systems are the most flexible and hackable and have a great reputation, can be calibrated, have customizable alarms, but they don’t interact with your pump.

We’ll be testing the Dexcom G5 later in August – and will update on our results.

The Ergohacks Verdict on CGMs

We think a CGM and insulin pump combination is the best choice of management for Cass. It’s allows more flexibility, tighter control without causing more episodes of hypoglycemia and has been instrumental in reducing out of range figures. Most importantly, it has made a significant difference in her quality of life. It’s made such a big difference, that we’re funding it ourselves.

In the UK, CGMs are rarely available on the NHS. Cass doesn’t qualify despite pretty gruesome (to us) night time lows with no identifiable cause and a secondary condition that directly impacts on both insulin delivery and carbohydrate absorption. The economic argument for them in the short term is hard to make and the NHS resists change. There is also a postcode lottery and availability is dependent on where you happen to live and receive treatment. Unless you have a child under 5 and severe, clearly documented hypos with hypo unawareness, you’re unlikely to get one on the NHS. Most hospital’s will however be happy to write a letter saying that should have one and that will let you self fund it.

Few things have been as instrumental to lifting the burden of living with Type 1 Diabetes as Cass’ CGM. We can make better informed decisions, the graph trends alerts us to cannulas not working properly, sugar that isn’t being absorbed in her stomach and it helps us mediate the impact of her chronic digestive issues, skin laxity that makes cannulas shift and partially occlude, severe pain and help us weather the storms of frequent viral infections. She can test less, saving the fragile skin on her fingers some trauma and dislocations (finger prick test often dislocate her finger tips) and we can sleep a bit more at night, knowing it’ll alarm when her levels trend out of range. We couldn’t make it through the day without one.