CGM Guide Series
CGM Guide for Type 1 Diabetes
Not all CGMs are built the same. This guide explains the five-question framework we use to assess whether a device has enough published evidence to support insulin dosing, then walks you through every device that meets the mark.
GNL Grace
Not sure which CGM is right for you? Tell Grace what matters and she will walk you through the accuracy data, features, and evidence for each device.
Five questions. Every CGM must answer all five.
This framework was built with the DSN Forum UK. It is not a checklist of features. It is a test of whether a CGM has been studied in a way that allows you to trust the reading when you are deciding how much insulin to take.
- People with type 1 diabetes included, studies in T1D, not just type 2 or healthy volunteers
- Meal challenge included, rapid glucose rises tested, not just stable periods
- Hypoglycaemia challenge included, accuracy tested in the low range where it matters most
- Venous or capillary blood reference, the gold standard reference method, not another CGM
- Population and indication match, studied in the people it will actually be used in, with the right regulatory indication
Devices that currently meet 5/5
Four CGMs have published enough evidence, in the right populations, with the right study design, to earn a place in this guide. Each has a dedicated page with the full accuracy picture, what the evidence actually shows, and what makes it distinctive.
Dexcom G7
- The widest AID integration, Omnipod 5, t:slim X2, CamAPS FX
- Unique alarm features, Urgent Low Soon and Delay First High reduce alarm fatigue while keeping you safe
Abbott FreeStyle Libre 2 Plus and 3 Plus
- 15-day wear, fewest sensor changes of any device in this guide
- Libre 3 Plus is the smallest CGM available, significantly more discreet than competitors
- Simple to use, no calibration, no transmitter, scan or stream
Roche Accu-Chek SmartGuide
- 7-hour overnight hypo prediction, alerts before a low arrives, not after
- 45-minute daytime action prediction and 2-hour awareness window built into the app
- Mandatory 2 calibrations in first 12 hours, 14-day wear
MiniMed Guardian Sensor 4
- The current most-prescribed sensor in the MiniMed 780G portfolio; the established choice for existing 780G users
- 7-day wear; MiniMed-made; CE non-adjunctive from age 2, FDA adjunctive only from age 7 (per Pemberton 2026 Table 1)
- Full page pending; core device facts live on the 780G guide
MiniMed Simplera Sync
- Designed for the MiniMed 780G, the most deeply integrated CGM-pump combination available
- SmartGuard AI algorithm handles insulin delivery decisions automatically, reducing the impact of sensor accuracy on daily management
- One of the two forward-path sensors in the MiniMed 780G portfolio (alongside the 15-day Instinct); Guardian Sensor 4 remains the current most-used installed base
MiniMed Instinct (Abbott-made)
- Designed exclusively by Abbott for MiniMed’s 780G AID system; not interchangeable with FreeStyle Libre 3
- World’s smallest and thinnest integrated CGM; one-hour warm-up; one-handed insertion; no fingersticks
- CE Mark 10 March 2026; US shipping since December 2025; European commercial launch summer 2026; UK TBC. One of the two forward-path sensors for the MiniMed 780G portfolio.
Eversense 365
- The only implantable CGM – one sensor lasts a full year, inserted under local anaesthetic into the upper arm
- On-body vibration alerts and nothing visible on the skin – the most discreet CGM form factor. Adults only; no AID integration.
Two more devices are close. CareSens Air and GlucoMen iCan have both passed the framework criteria, published data is pending or under review. CareSens Air · GlucoMen iCan
Find your best match
Pick the three things that matter most to you. The selector scores each device against your priorities and recommends your top two.
Why only these devices? Every CGM in this selector has passed the five-question clinical framework on this page, or is close enough that its data is worth comparing. Devices without published accuracy studies in the right populations, or without a non-adjunctive indication, are not included. The selector is a starting point for a conversation with your diabetes team, not a substitute for it.
Select 3 priorities (0 of 3 chosen)
What the accuracy data actually means
Marketing material typically leads with a statistical average of how far the sensor is from a reference measurement. That average tells you very little about what matters clinically. GNL reports CGM accuracy using ±20/20 and ±40/40 agreement only – see the accuracy page for why.
What matters is this:
- ±20/20 agreement rate, the proportion of readings accurate enough to support an insulin dosing decision without a confirmatory finger prick. For all four devices in this guide, this is in the range of 93-96%. These are the readings you can act on.
- ±40/40 agreement rate, the proportion of readings within a range where an error would not lead to a seriously wrong insulin dose. For all four devices, approximately 99-99.8% of readings fall within this band.
The readings that fall outside the ±40/40 band, typically between 0.2% and 1% depending on the device, are the ones that could, in theory, lead to a harmful dosing error. This is what we call the black swan. It applies to all four devices in this guide. It is not a reason to avoid CGM. It is a reason to understand when a finger prick is still the right call.
Related guides
Pairs with the AID Guide
Every UK AID system needs a compatible CGM. If you are choosing both, the AID guide carries a matching selector and the IOB Trade-Off article compares how the four algorithms handle insulin.
Pairs with the Adjunctive Therapy Guide
CGM made type 1 diabetes visible, AID automated much of it, and adjunctive therapy (GLP-1RA and GLP-1/GIP) is the third advanced lever for adults. Off-label, specialist-led, and covered end to end in the four-part guide.
Evidence backbone
This page is built on the GNL CGM Evidence Pack. John Pemberton is lead or contributing author on every entry below. The Evidence Pack itself sits inside Grace, the GNL clinical knowledge engine; the source papers are linked here for independent verification.
- Pemberton et al 2026 – International clinical opinion on transparency, standardisation, and calibration alignment in CGM. Modified Delphi consensus, 21 international authors. Diabetes, Obesity and Metabolism. DOI: 10.1111/dom.70460
- Pemberton et al 2023 – CGM accuracy: contrasting CE marking with the FDA and TGA. Narrative review. Diabetes, Obesity and Metabolism. DOI: 10.1111/dom.14962
- Pleus et al 2025 – IFCC Working Group clinical assessment guideline for CGM system performance. John Pemberton co-author. Clinica Chimica Acta. DOI: 10.1016/j.cca.2025.120728
- Moser & Pemberton 2024 – Rethinking the safety and efficacy assessment of HCL systems. The CGM-AID safety bridge. Diabetic Medicine. DOI: 10.1111/dme.15305
- DSNFUK CGM Comparison Framework v2 (March 2026) – The practical UK clinical reference, authored by John Pemberton. DSNFUK chart
Overall evidence grade: C (clinical opinion, consensus guidelines, methodology papers). Confidence: HIGH – John is at the centre of the international consensus on CGM standardisation.