CGM Guide Series

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.

CGM Evidence

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.

CGM Systems for Insulin Dosing Comparison Charts — DSN Forum UK and The Glucose Never Lies®
Click the chart to access the full DSN Forum UK CGM Comparison Charts
  • 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
Read the full framework Data sufficiency explained

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

Framework: 5/5 iCGM: Yes
±20/20
95.3%
Outside ±40/40
<0.5%
  • 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
Explore Dexcom G7

Abbott FreeStyle Libre 2 Plus and 3 Plus

Framework: 5/5 iCGM: Yes
±20/20
93.4%
Outside ±40/40
<0.5%
  • 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
Explore Abbott FreeStyle Libre

Roche Accu-Chek SmartGuide

Framework: 5/5
±20/20
91%
Outside ±40/40
<1.0%
  • 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
Explore Roche Accu-Chek SmartGuide

Medtronic Simplera Sync

Framework: 5/5
±20/20
88%
Outside ±40/40
<1%
  • 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
Explore Medtronic Simplera Sync

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)

✓ AID / pump integration – I use or plan to use an automated insulin delivery system
✓ Smallest and most discreet – form factor and visibility matter to me
✓ Alarm sophistication – the most advanced alert options to reduce alarm fatigue
✓ Best for children and families – paediatric approval, follower apps, school use
✓ Optional calibration – the ability to calibrate if the reading feels off
✓ Longest wear / fewest changes – least disruption from sensor changes
✓ Predictive alerts and AI – the most advanced predictive and smart features
✓ Data platform and downloads – clinic download options, app data, and EHR integration
✓ Followers and remote monitoring – family, carers, or school see readings in real time
✓ Customer care and product support – strong support infrastructure if something goes wrong

What the accuracy data actually means

CGM accuracy is typically reported as MARD — mean absolute relative difference. It is a statistical average that tells you very little about what matters clinically. We do not use it as a primary measure.

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.

Full accuracy guide and the black swan

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