Continuous Glucose Monitoring (CGM) with Medtronic Enlite® sensor and Guardian® Link Transmitter

Type 1 Diabetes management is an all-the-time thing, every minute of each day. The body no longer produces (enough) insulin and so a highly complicated automated physical function now has to be done manually. One of the big potholes we hit after our daughter was diagnosed and was set-up with an insulin pump, was not knowing what her glucose levels were most of the time and thus being unable to help her artificially raise or lower them.

We experimented with Abbot’s Freestyle Libre flash glucose monitor, but hit two problems it could not overcome: (i) we couldn’t calibrate it, which reduced its accuracy and reliability and (ii) it’s a passive system. Our daughter struggles with nocturnal hypoglycemia and we wouldn’t know she was low unless we happen to be scanning with the Libre sensor at that moment. Her levels have dropped so low that we had difficulty waking her and when we finally managed it, she was highly resistant to treatment.

Medtronic’s CGM system offered the solution – it can be calibrated and it’s integrated with her Medtronic insulin pump. It continuously monitors her glucose levels with updates every 5 minutes and has customizable built-in alarms. It even goes one step further – suspending insulin basal delivery when low or when approaching low to prevent hypoglycemia.

Product Information

Retailer: Medtronic +                   

Price: ±£490 Starter pack (1 month supply). After that £55 per sensor (lasts 6 days). A Guardian Link Transmitter is £490.

Discount: Medtronic’s CGM is rarely available through the NHS and only in exceptional circumstances. Self-funding is an option (even if your insulin pump is via the NHS). Medtronic offers a 3-tier loyalty scheme that reduces the cost. The platinum scheme offers the biggest discount: £490 for the starter pack and thereafter £210 monthly (which will result in a second guardian link transmitter gratis after 12 months). More information here.

About Medtronic

Medtronic is a global company founded in 1949 and headquartered in Dublin, Ireland and Minnesota in the US. They are the world’s largest medical technology developer and employ almost 100,000 people. They are at the forefront of diabetic equipment research as well as spinal, cardiac and neuromodulation devices.

Design

This CGM system requires three components: (i) A compatible Medtronic insulin pump (640G in the UK, 630G in the US), (ii) Enlite sensors (each sensor lasts 6 days each and are not reusable) and (iii) one Guardian Link Transmitter that attaches to the sensor. The complete package really has three primary functions:

Continuous glucose monitoring

CGMs are increasing both in use and popularity. It’s difficult to control your glucose levels when you don’t know what they are at a given point in time. Finger prick tests only give one number at one point of time – it doesn’t tell you if its going up or down, how fast it’s changing or how long it’s been at the level it’s at. Flash monitor systems, like the Libre, only give you a number when you scan it – it doesn’t alert or alarm.

CGMs on the other hand, automatically checks interstitial glucose levels every 5 minutes and display them. They have alarms that can be set to alert the user to significant data and when levels are in range and stable, there’s no need to even think about the numbers, but if you’re curious, the data is always there. Knowing what your blood glucose levels are and will probably be doing over the next hour, is a vital step in controlling them.

The extra data is very useful. We can spot trends, check insulin levels and correct bad habits. It’s much easier to check and correct basal rates, carb and correction factors. She feels safer and more confident with it, happier to venture a bit further without a parent nearby to step in because life is simpler because of it. She gives it four stars out of five because the sensors only last six days, (she’d like them to last a year), they’re a bit painful to insert and they stop sticking well around day 5 when immersed in water a lot. I give it five out of five stars because, as a parent, I feel that’s a small price to pay for the safety net it provides.

Customizable alarms

It sounds like a little thing, but having the option to set your own alarms is a huge benefit. High limits can be set from 5.6 to 22.2 mmol/L whilst low limits can be set from 2.8 to 5.0 mmol/L. There’s the option to alert on high/low as well as before high/low. For low values, it’ll alert 30 minutes prior whilst for highs it can be set for 5 – 30 minutes prior. You can set up to 8 different settings over a 24 hour period. A customizable snooze for high/low alerts is also available.

For those who detest alarms, the ranges can be set wide to only alert the user to potentially serious excursions, whilst for those after tight control, alarms can be set to alert the user up to 30 minutes prior to glucose levels stepping out of range. Alarms are vibrate, audio or both and can also be temporarily silenced with a global setting (except for the low alarm) when you don’t want them – such as during an important meeting.

A note on repeated alarms
Be aware that when the high or low alarm sounds a second time, it doesn’t mean levels are still rising or falling, it just means that the new value is still outside of the set target range. For example: if your SG(sensor glucose) is 3.2 and then fifteen minutes it’s 3.7 and your low level is set at 4.0, it will sound the low alert both times.

SmartGuard

The Smart Guard feature is one of the Minimed system’s appeals. It allows the pump to automatically suspend insulin delivery either on low or before low and then will automatically resume insulin delivery when levels rise. As stated above, the low limit can be set between 2.8 and 5.6 mmol/L. If  “Suspend on low” is selected, insulin delivery will automatically stop when the limit is reached. If “Suspend before low” is selected, insulin delivery will automatically stop if levels are predicted to reach the target low in the next 30 minutes.

Insulin delivery will be resumed afterwards when two conditions are met: (i) insulin level reaches a number 1.1 mmol/L above the set low and (ii) insulin levels will reach at least 2.2 mmol/L above the target low in the next 30 minutes. Insulin delivery will always resume after 2 hours though, whether the above conditions have been met or not. SmartGuard is unavailable for 30 minutes after insulin is resumed (either by user or pump), but if the user is unresponsive to the SmartGuard feature for more than 30 minutes after resumption, it will be unavailable for the next 4 hours.

It’s not a perfect solution to hypoglycemia – if glucose levels are rapidly dropping, suspending basal insulin won’t be enough to prevent hypoglycemia. Suspending basal insulin offers no guarantee that glucose levels will spontaneously recover – testing and treating hypoglycemia remains vital. If the SmartGuard feature activates multiple times a day – it can really mess up basal delivery, but conversely, that’s also an excellent indicator that basal insulin rates are not appropriate.

We’ve experimented with the feature – using suspend on low and suspend before low as well as setting the low threshold anywhere between 3.2 and 4.8. After ten weeks of use, we’ve mainly settled on suspend before low whilst setting the low figure at 3.6. It means that insulin tends to suspend when glucose levels reach the 4s and are dropping steadily or it actives in the 5s when levels are rapidly dropping. The great advantage is in the resume which happens at 4.7ish when levels are set to reach 5.8 within half an hour, which for us avoids a second low as well as any spikes.

Features

  • Continuous glucose monitoring
  • Customizable alarms
  • SmartGuard
  • Data compatible with Nightscout

Environment & People

ergonomicinclusivedesignBuild quality

Cost-Effective

Medtronic’s CGM system is not a budget option. It’s a prime product with a high build quality, but it’s worth every penny. The starter kit is £490 and after that the loyalty scheme brings the cost down to around £7 per day (£210 per month). It is rarely available on the NHS for exceptional cases, but Medtronic is set-up for NHS pump-users to self-fund their CGM and sensors should they choose to do so.

Included in the price is not only the hardware, but also excellent 24-hour customer support. We had a lovely lady talk our terrified 6-year old through her first insertion for 2 hours – showing her videos, explaining the process and answering a million questions until she was comfortable to proceed. We’ve called up for the odd error that has popped up or when sensor readings were surprisingly inaccurate. Every time, expert advice was on hand and in all but one case, the problem was fixed with a phone call. The one occasion where it wasn’t, a replacement sensor was dispatched free of charge without us even asking for it.

Requirements

internet accesswifi accessdexterityrequirementbwPhysical requirement

* Compatible Medtronic insulin pump
* Some technical expertise

Verdict

Diabetes management is complex, time consuming and difficult. Every extra piece of technology we’ve picked up along the way has made a significant improvement, but Medtronic’s CGM system has by far made the most significant impact on her life quality, our stress levels and our joint competency in managing her day-to-day glucose levels.

The SmartGuard basal suspend has made a notable difference in the frequency and severity of lows and in combination with conservative alarms, makes it easy to quickly react to rising or falling levels before they become problematic. Management is much easier when we know not only what her levels are, but how they are changing and how fast. There’s no need to wonder and worry like we did with just finger pricking, there’s no need to constantly check and evaluate, like we had to do with the Libre, we can forget about it when we want to until her pump alarm sounds.

The system isn’t perfect. The sensor regularly drops out for a few minutes, sometimes longer for no obvious reason. It doesn’t work in places with lots of bluetooth devices – like Southampton’s Ikea – and although the sensors are highly accurate the vast majority of the time – it isn’t all the time. CGM results are not actionable – before treating lows or bolusing insulin, a finger prick test is needed to confirm its values. In addition, CareLink™ Personal, Medtronic’s proprietary software application used to download the data from the pump, is antiquated and no longer works on a Mac or the latest version of browsers. Medtronic recommends not installing software patches – including security patches – an unsustainable solution. We hope that a new system will take its place in the near future, but there’s been no news on any developments.

Despite the system’s few imperfections, it’s on the cutting edge of Diabetes technology, made to a high standard by one of the world’s leading companies in diabetes care and supported by a robust 24-hour helpline. Living with Type 1 Diabetes (and being the parent of a child with Type 1 Diabetes) is a time-consuming, stressful, unrelenting roller coaster, but Medtronic’s CGM system has made it easier, more predictable and safer.

May 2017 Update: New verdict – wait to buy

We’ve run into some issues in April and May with the Enlite sensors. The four sensors we received at the end of March did not meet the performance we’ve come to expect. They dropped out frequently as soon as glucose levels were changing – so during meals, exercise and quick drops at night that often lead to hypoglycemia, so the times when we rely on them most. They popped back in again automatically within an hour, but not all the time. One malfunctioned entirely and had to be replaced a day early – we were promised a replacement sensor, but for the first time it was never sent out.

We were hoping it was just a sub-par batch and opened up the May box with glee yesterday. The first sensor in the box has not inspired confidence. It just wouldn’t calibrate despite her glucose levels being fairly stable. We called the helpline and was reassured that we’d done everything right, that it should be working and that values were comfortably in range and to wait an hour then try one more time and if that doesn’t work, replace the sensor. It worked! Multiple glucose tests and almost 3 hours later, it finally accepted a calibration. Disappointingly, it’s already dropped out three times in the last four hours.

We’ve also received an email from Medtronic this week stating that they’re having supply problems. The representative we spoke to today said that orders were back-logged at least a month. Our last order took longer than usual to dispatch and although we’ve already put in an order for June, we don’t know if it’ll actually arrive on time. We’re hoping it’s a temporary problem, but there’s no way to know. For the time being, until these issues are resolved, we’d recommend waiting to buy.

The review is based on the Enlite Sensors, Guardian Transmitter integrated with the Medtronic 640G insulin pump and tested for 10 weeks.  This article was first published on 21 March 2017.


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