Continuous glucose monitoring (CGM)

What is continuous glucose monitoring (CGM)?

Continuous glucose monitoring (CGM) uses a small sensor worn on the skin, usually on the upper arm or tummy, to measure glucose in the fluid just under the skin. It shows your glucose level and which way it is heading, day and night, without the repeated finger-prick tests many people are used to.

There are two main types. Real-time CGM sends readings automatically to a phone or receiver every few minutes and can sound alerts. Flash (intermittently scanned) monitoring shows a reading when you scan the sensor with a phone or reader. Both help people with diabetes, and their teams, spot patterns, see the effect of food, activity and medicines, and adjust treatment.

CGM is a tool to support diabetes care, not a treatment in itself, and not a cure. It measures glucose in the fluid under the skin, which lags a little behind blood glucose, so readings are not identical to a finger-prick and have their own limits.

This guide explains how CGM works, what it can and cannot do, how accurate it is, and how to get the most from it. It is general information, not personal diabetes advice.

Types, options & approaches

There may be different ways to do this. The right approach depends on the clinical question and your circumstances.

Options at a glance

These are the main approaches described in this guide. The right option depends on the diagnosis, your goals and what your clinician thinks is safe.

Preparing for your test

• Ask your diabetes team which sensor suits you and whether you qualify on the NHS.
• Ask to be shown how to apply the sensor and how to read and understand the data.
• Find out whether you still need any finger-prick checks, for example when readings do not match how you feel.
• Check how the sensor links to your phone or reader and whether your phone is compatible.
• Tell the team about skin problems or adhesive allergies, as some people react to the sticky patch.
• Ask what the alerts mean and how to set them, if your sensor has them.
• Plan sensor changes around work, sport, travel and any scans, as some scans require sensor removal.

What happens

A fine, flexible sensor filament is inserted just under the skin using a simple applicator; most people feel little more than a quick prick, and there is no need for stitches. The sensor sits on the skin held by an adhesive patch and is usually worn for about one to two weeks before being replaced.

With real-time CGM, readings appear automatically on a phone or receiver every few minutes, often with a trend arrow showing the direction of change, and alerts for highs and lows. With flash monitoring, you scan the sensor to see your reading and recent trend.

The data builds a picture of your glucose through the day and night, including overnight, which finger-prick tests can miss. You and your diabetes team review the patterns, such as time spent in your target range, to adjust food, activity, insulin or other medicines. Some people may occasionally still need a finger-prick test to confirm a reading.

Is this test right for me?

A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.

Before you decide

Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.

CGM measures glucose in the fluid under the skin, which trails blood glucose by several minutes, so readings can differ from a finger-prick, particularly when glucose is rising or falling quickly. No sensor is perfectly accurate, and accuracy can be lower in the first hours after insertion. Always treat symptoms of a severe low or high seriously and confirm with a finger-prick if the reading does not match how you feel. Ask your team how to use alerts, when to finger-prick, and how to interpret trends rather than single numbers.

Published figures to discuss

CGM accuracy varies between devices, body sites, and how fast glucose is changing, and it is often lower in the first hours after a new sensor starts. Accuracy is sometimes summarised as a single figure (MARD), but experts caution this can be misleading and should not be the only measure. Because real-world accuracy depends on so many factors, we have kept this qualitative rather than quoting a single percentage.

These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.

What happens afterwards

There is no physical recovery from wearing a CGM. What matters afterwards is learning to read the data well and using it, with your diabetes team, to guide treatment over the following days and weeks.

• Mild itching or a mark under the adhesive that settles
• Getting used to interpreting trend arrows and alerts
• Occasional differences between sensor and finger-prick readings
• Less accurate readings just after a new sensor starts
• Adjusting treatment gradually as patterns become clear

Aftercare

• Rotate sensor sites and follow the maker's instructions for skin preparation.
• Keep a finger-prick kit available for when readings and symptoms do not match.
• Learn what trend arrows mean and act on the direction, not just the number.
• Set alerts sensibly with your team to avoid alarm fatigue.
• Tell your team about skin reactions so alternatives can be tried.
• Remove the sensor before scans (such as MRI or CT) if the maker advises, and replace it afterwards.
• Review your glucose patterns with your diabetes team and adjust treatment together.

• Compatible phone or reader set up
• Spare sensors and applicator to hand
• A finger-prick kit for back-up checks
• Knowledge of what each alert means and how to respond
• A plan for sensor changes around work, sport and travel
• Skin-care plan if the adhesive causes irritation
• A booked review with your diabetes team to look at the data

⚠ Get urgent help if…

• Symptoms of a severe low (hypo) such as confusion, shakiness, sweating or near-collapse — treat immediately and do not wait for the sensor.
• Symptoms of very high glucose with vomiting, deep breathing, tummy pain or drowsiness (possible diabetic ketoacidosis) — seek urgent help.
• A sensor reading that strongly disagrees with how you feel — confirm with a finger-prick.
• Spreading redness, swelling, pain or pus at the sensor site (possible infection).
• Repeated unexplained lows or highs despite the data.
• A severe skin reaction under the adhesive.

Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.

General guidance — it doesn't replace the specific advice your specialist gives you.

Results & realistic expectations

A good result from CGM is clearer insight into your glucose patterns, more time in your target range, fewer or less severe hypos, and treatment that is better tailored to you. Teams often look at 'time in range' and overnight patterns rather than single readings.

CGM gives information to guide care; it does not lower glucose by itself, and it cannot replace good diabetes management or guarantee perfect control. Because readings come from the fluid under the skin, they are a close guide rather than an exact match to blood glucose, and they need interpreting alongside how you feel.

Each sensor lasts about one to two weeks before it is replaced, so CGM is an ongoing tool rather than a one-off test. Devices and software change over time; for example, some sensors are being updated or replaced by newer versions. The value of CGM lasts as long as the data is reviewed and acted on, with your team, to keep guiding treatment.

Related tests, treatments or support

CGM is often used alongside insulin or other diabetes medicines, and for some people it links to an insulin pump to adjust insulin automatically (hybrid closed loop), set up by a specialist team. It complements, and for many reduces, finger-prick testing, and the data is reviewed together with HbA1c blood tests, which give a longer-term average.

Follow-up & long-term care

Follow-up is with your diabetes team, who review your glucose patterns, time in range and any alerts, and adjust treatment with you. They also check how you are getting on with wearing the sensor and reading the data. How often you are seen depends on your diabetes and how stable your glucose is.

• Replacing the sensor about every one to two weeks
• Rotating sites and caring for the skin under the adhesive
• Keeping the phone or reader and app updated
• Occasional finger-prick checks for back-up and calibration where needed
• Regular review of glucose data with the diabetes team
• Periodic HbA1c blood tests for the longer-term picture

Repeat, follow-on and what comes next

• Sensors are routinely replaced about every one to two weeks.
• A sensor that fails early or reads inaccurately may need replacing sooner.
• Alert settings are often adjusted to balance safety against alarm fatigue.
• Switching device type or site is common if accuracy, comfort or skin reactions are a problem.

Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.

What good aftercare looks like

• Education on applying sensors, reading trends and responding to alerts.
• Clear guidance on when to finger-prick and how to treat lows and highs.
• Regular review of glucose data with the diabetes team and treatment adjustment.
• A plan for skin care and for sensor changes around daily life and scans.
• A named contact for device problems and diabetes support.

What affects the cost

Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:

• The type of sensor and how often it must be replaced
• Whether a separate reader is needed or a compatible phone is used
• Whether the system links to an insulin pump (hybrid closed loop)
• Diabetes team support and education to set up and interpret the device
• Ongoing review appointments to adjust treatment
• Any additional finger-prick test strips kept for back-up

• The cost per sensor and how many are needed over time
• Whether a reader, app or subscription is included
• What set-up and education by the diabetes team is included
• The cost of follow-up appointments to review the data
• What back-up finger-prick supplies are recommended
• What happens, and what it costs, if a sensor fails early
• Whether you might qualify for NHS-funded CGM instead

On the NHS? CGM and flash monitoring are available on the NHS for everyone with type 1 diabetes and some people with type 2 diabetes, subject to national guidance; CGM is also available privately for those who do not qualify or who prefer to self-fund.

You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.

Consent traps and marketing red flags

These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.

Choosing a specialist safely

• Check the specialist is on the GMC Specialist Register for this area.
• Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
• You're entitled to time to consider and to have your questions answered before you agree — the specialist who looks after you should explain it, not a salesperson.
• Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
• You're entitled to your total cost in writing — including any follow-up — before you decide.

How Vuemedics verifies every consultant →

Take this to your consultation. A good specialist will welcome every one of these.

• Which type of sensor suits me, and do I qualify for it on the NHS?
• How should I respond to a low or high reading, and to the trend arrows?
• Do I still need finger-prick tests, and when?
• How will we use the data to change my treatment?
• What should I do if my readings do not match how I feel?
• What targets, such as time in range, are we aiming for?
• Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
• Will you be the specialist who carries out my test, and who looks after me afterwards?
• What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
• What does a realistic result look like — and what can this test not achieve?
• What are my options, including waiting, doing nothing for now, or choosing a different approach?
• Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
• What is the total cost in writing, including any follow-ups, and how much time do I have to decide?

Find a verified specialist for continuous glucose monitoring (cgm)

Every consultant is GMC-checked and independently reviewed. Search by postcode and distance, or switch to a map. Ordered by rating, relevance and recency — never by who pays.

How we made this page

Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →

Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.

Sources & standards: Diabetes UK — Can I get CGM on the NHS? NHS — Continuous glucose monitoring and hybrid closed loop NICE — Dexcom G6 for real-time CGM: the technology Benefits and limitations of MARD for CGM accuracy — PMC Continuous glucose monitoring technologies — Endotext (NCBI)

Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.

Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.