A small round CGM sensor patch worn on the back of the upper arm

The Diabetic Patch: How Continuous Glucose Monitor Sensors Work

Key Takeaways

  • No official source uses the words "diabetic patch". The device people mean is a continuous glucose monitor (CGM) sensor, which sits under the skin and is held on by a sticky patch.[1]
  • A CGM reads glucose in the fluid under your skin, not in blood. Readings run a few minutes behind, and the gap grows when glucose is moving fast.[2][3]
  • Everyone using a CGM still needs a finger prick meter at times. The ADA and NICE both say so.[3][4]
  • The ADA recommends CGM for anyone on insulin. In England the NHS offers it to people with type 1, and to adults with type 2 on insulin who meet set criteria.[3][2][5][4][6]
  • In trials in type 2 diabetes, HbA1c was about 0.3 percentage points (about 3.3 mmol/mol) less with CGM than with finger pricks. One of the largest trials, MOBILE, was paid for by the sensor maker.[7][8]

Search for a diabetic patch, also sold as a glucose patch, and you will see photos of a small white disc on the back of someone's arm. That is a continuous glucose monitor sensor, CGM for short. We looked for the words "diabetic patch" in the 2026 ADA Standards of Care, the NICE guidelines, and the NHS, NIDDK, Diabetes UK and FDA pages. None of them use the term. So this guide explains what the device under that name really is, how it works, who can get one, and what it cannot do.

We also read the main trials behind it, and we name who paid for each one.

This guide is general education. If you use insulin or other glucose medicines, follow the plan your diabetes team gave you.

What is a diabetic patch?

A diabetic patch is a CGM sensor. The NIDDK, part of the US National Institutes of Health, describes a CGM as a device with three parts. First, a tiny sensor goes under your skin, often on your belly or arm, "with a sticky patch that helps it stay there". Second, a transmitter sends the readings without wires. Third, software on a smartphone, an insulin pump or a separate reader shows them.[1] The NHS calls it "a small device you attach to your arm or tummy that senses how much glucose is in the fluid under your skin".[2]

The ADA lists three types. Prescription real-time CGM streams readings and has alarms. Over the counter CGM has no alarms, and the ADA says it can be used by people not taking diabetes medicines that raise the risk of low blood sugar. Professional CGM is worn for a short time and read in a clinic.[3] The NHS splits the first type in two. A real-time monitor sends readings to a phone or reader every few minutes. A flash glucose monitoring sensor stores readings until you scan it. The NHS page, reviewed in October 2024, says the only flash monitor available is the Abbott FreeStyle Libre 2.[2] Diabetes UK says that sensor was phased out in August 2025 and the FreeStyle Libre 2 Plus is now the only sensor that works as a flash monitor.[6]

A disposable sensor is replaced every 7 to 14 days, and some implanted sensors last up to 180 days.[1] The current Libre 2 Plus and Libre 3 Plus sensors are made to last 15 days.[9] Some models can be used by children as young as 2.[1]

How does a CGM sensor work?

The sensor does not read blood. It reads the fluid between your cells, called interstitial fluid. The ADA says this "correlates well with plasma glucose, although at times, it can lag if glucose levels are rising or falling rapidly".[3] The NHS says the readings are "a few minutes behind your blood glucose levels".[2] One small study measured the gap directly. In 6 fasting adults with type 1 diabetes, glucose took a median of 6.8 minutes, and at most 9.8, to move from blood into the fluid under the skin.[10] Diabetes UK puts the lag at up to 15 minutes, and says the gap between the sensor and a finger prick is more likely to be bigger when you are eating or exercising.[6]

Accuracy is reported as MARD, the average gap between the sensor and a lab test. A study of the Dexcom G7 in 316 adults over 10.5 days found a MARD of 8.2% on the arm and 9.1% on the abdomen. It was paid for by Dexcom, and 4 authors work there.[11] A study of the 15 day Libre 2 Plus and 3 Plus sensors in 149 adults and 124 children found a MARD of 8.2% and 8.1%. Abbott funded it, and 3 authors work there.[9] So in maker funded studies, current sensors are off by about 8 to 9 percent on average against a lab reference.

Some models need a finger prick to calibrate them.[1] The Libre 2 Plus and 3 Plus sensors are calibrated in the factory.[9] Some substances can throw readings off. The ADA says sensor users should be taught about interfering substances, and names hydroxyurea, a drug for some blood conditions, as a recent example.[3] For finger prick meters, the FDA names vitamin C and acetaminophen (paracetamol) as substances that may affect the result.[12] The Libre Plus sensors were redesigned to cut vitamin C interference.[9]

Who can get a CGM?

The ADA recommends CGM at diagnosis and any time after for children and adults who use insulin. That carries its top evidence grade. It also recommends CGM, with a moderate evidence grade, for people on non-insulin medicines that can cause low blood sugar (such as a sulfonylurea like gliclazide or glimepiride), and for anyone whose treatment goes better with it. The device and how it is used should match the person's circumstances, preferences and needs.[3] People on insulin should wear it as close to daily as possible.[3]

In England the rules are narrower for type 2. NICE tells clinicians to offer adults with type 1 diabetes a choice of real-time CGM or flash, based on their preferences, needs and the features of the devices.[5] For adults with type 2 diabetes, NICE tells clinicians to offer flash to those on multiple daily insulin injections who meet one of four criteria. These are recurrent or severe low blood sugar, impaired awareness of lows, a condition or disability that stops them doing finger prick tests, or needing to test at least 8 times a day. It also offers flash to adults on insulin who would otherwise need a care worker or health professional to check their glucose. Real-time CGM is an option if it costs the same or less.[4]

NICE found evidence that flash was cost effective for people on insulin "but no evidence for populations not using insulin", and said the effect on HbA1c was minimal.[4]

Diabetes UK says that if you are 18 or over, live in England, Scotland or Wales and have type 1 diabetes, you should be offered a CGM. If you do not qualify, "your main option is to self-fund". The charity puts the cost at roughly Ā£50 to Ā£150 (about $65 to $195) a month, with no method shown. It also reports that nearly half of people who tried to get diabetes technology had been refused at some point, again with no method shown.[6]

CGM or finger prick meter: which is right for you?

For most people on insulin, the answer in both the US and the UK is a CGM plus a meter as back-up. The ADA says people using a CGM "must also have access to BGM at all times", meaning a finger prick meter.[3] It lists the moments a finger prick is still needed. These are when you suspect the sensor is wrong, while a new sensor warms up, when the signal drops, for calibration or after a warning message, and when sensor supplies are late. A finger prick is also needed whenever glucose is changing faster than 2 mg/dL (about 0.1 mmol/L) a minute.[3] The NHS adds two everyday cases: when you drive and when you have a hypo.[2]

NICE tells adults with type 2 on CGM that they will still need finger prick checks, though less often, and that anyone who does not want a sensor should be offered a meter.[4]

Without a sensor, intensive insulin use means a lot of pricks. The ADA says that for many people using a meter alone, this "requires doing finger sticks" 6 to 10 times a day.[3] The NHS tells people with type 1 to check at least 4 times a day.[2]

For people not on insulin, the ADA says finger prick testing "has not consistently shown clinically significant reductions in A1C (HbA1c) levels", though it can help when changing meals, activity or medicines.[3] Use an approved meter with in-date strips. Never use a reading from an alternative sampling site to calibrate a CGM or to work out an insulin dose.[3][12] Low blood sugar usually means below 4 mmol/L (72 mg/dL) in the UK or below 70 mg/dL (3.9 mmol/L) in the US.[2][1] Our guide to low blood sugar covers the warning signs. In the UK, the NHS says to call 999 if someone may have very low blood sugar and is not responding normally or is unconscious, and a glucagon injection is not available or you do not know how to use it, or they have not recovered within 10 minutes of a glucagon injection, or they have been drinking alcohol.[2] In the US, the ADA and NIDDK say to call 911 right away if someone is unconscious and glucagon is not available or no one knows how to use it, or right after giving glucagon.[1][3]

Feature. Real-time CGM. Flash monitor. Finger prick meter.
What it measures. Fluid under the skin.[2] Fluid under the skin.[2] Blood from a finger.[12]
How you get a reading. Sent to a phone or reader every few minutes.[2] You scan the sensor.[2] One strip per test.[12]
Delay. A few minutes.[2] A few minutes.[2] None.[2][12]
Alarms for lows. Yes, can be switched off.[2] Optional on some devices.[2] No.[2][12]
How long it lasts. 7 to 15 days per sensor.[1][9] 7 to 15 days per sensor.[1][9] Meter lasts years, strips are single use.[12]
Finger prick still needed. Yes, at set moments.[3] Yes, at set moments.[3] Every test.[3][12]

What do the trials show?

In type 2 diabetes, people given a CGM ended up with HbA1c about 0.3 to 0.4 percentage points (about 3.3 to 4.4 mmol/mol) less than people on finger pricks, in trials that were not blinded.[7][8] One of the largest is MOBILE. At 15 US primary care centres, 175 adults on once a day background (basal) insulin were randomly given a CGM or a finger prick meter for 8 months. HbA1c went from 9.1% (76 mmol/mol) to 8.0% (64 mmol/mol) in the CGM group and from 9.0% (75 mmol/mol) to 8.4% (68 mmol/mol) in the meter group, an adjusted difference of 0.4 percentage points (about 4.4 mmol/mol). Time in the target range was 59% with CGM and 43% with the meter. One person in each group had a severe low.[8] HbA1c changed in both groups, the trial was not blinded, and Dexcom paid for it, supplied the sensors and helped design it.[8]

A 2024 review pooled 12 trials with 1,248 adults with type 2 diabetes. HbA1c was 0.31 percentage points (3.43 mmol/mol) less with a sensor than with finger pricks, and time in range was 6.36 percentage points higher. In all the trials people knew which device they had, and data on severe lows and long term complications were scarce. The review had no specific funding and the authors declared no competing ties.[7] Our HbA1c guide explains what a 0.3 percentage point (about 3.3 mmol/mol) change means.

What about patches that claim to deliver medicine through the skin?

A CGM sensor only measures. Its three parts are a sensor, a transmitter and software. None of them holds insulin, a herb or any other medicine.[1] The one skin-worn device that does deliver a medicine is a patch pump, an insulin pump without tubing that is prescribed and set up by a diabetes team.[3][13] It is a pump with a cannula, not a sticker. We found nothing in the ADA Standards, the NICE guidelines or the NHS pages about a stick-on patch that delivers a diabetes medicine through the skin, or that replaces one. If a product sold as a "diabetic patch" promises that, it is not a device described in any of these sources. Do not stop or change a prescribed medicine for it. Ask your pharmacist or diabetes team first.

Costs and practical tips

The NIDDK says a CGM costs more than a standard meter but may be covered by health insurance.[1] For the UK, Diabetes UK's self-funding estimate is in the section above.

Skin reactions are reported with every device that sticks to the skin.[3] In a survey of 139 children and teenagers with type 1 diabetes, 51.1% had skin reactions from patch pumps or sensors, and sensors caused most of them. Barrier bandages were the fix people used most.[13] In 2017, doctors reported an adhesive allergy in 15 users of an early Libre sensor and traced it in 12 of them to isobornyl acrylate, a chemical found in the adhesive.[14] Whether current sensors contain it is not something we could check. The ADA says skin reactions, from irritation or allergy, should be assessed and addressed so you can keep using the device.[3] The NIDDK notes that redness or irritation from the sticky patch can happen.[1]

You can usually wear a sensor in the bath, the shower and during sport, but some fall off, and you can buy adhesives to keep them on.[6] Once a sensor comes off it will not work again.[6] Diabetes UK adds that if you are not comfortable wearing diabetes equipment on your body, a CGM may not be suitable for you.[6] Our guide to technology and diabetes looks at the wider toolkit.

How to start with a CGM

  1. Ask your diabetes team which group you fall into. On insulin, the ADA recommends a CGM for everyone.[3] In England, type 2 access depends on the NICE criteria.[4]
  2. Ask for training. The ADA says anyone prescribed a CGM should be offered initial and ongoing education, including how to share the data.[3]
  3. Keep an approved meter and in-date strips. Use a finger prick when the sensor warms up, drops signal, gives a warning or seems wrong.[3]
  4. Check with a finger prick before you drive and during a hypo.[2]
  5. Watch your skin at each sensor change, and tell your team about any rash.[3]
Pro Tip

Expect the sensor to trail your blood by a few minutes, and by more after a meal or exercise. If what you feel does not match the number, Diabetes UK says to do a finger prick.[6]

Questions to ask your diabetes team

  • Do I meet the criteria for a CGM where I live, and is flash or real-time the better fit for me?[5][4]
  • Which of my medicines or supplements could affect sensor readings?[3]
  • At which moments should I confirm a reading with a finger prick?[3]
  • What can I put under the sensor if my skin reacts?[13]

Frequently asked questions

Is a diabetic patch the same as a CGM?

Yes, in everyday speech. No official source uses the words "diabetic patch". The thing people mean is a continuous glucose monitor sensor, a small device held on the arm or belly by a sticky patch. It reads glucose in the fluid under your skin.[1]

How long does a CGM sensor last?

Most disposable sensors are replaced every 7 to 14 days, and some implanted sensors last up to 180 days.[1] The newest Libre sensors are made to last 15 days, according to a study paid for by their maker.[9]

Does a CGM replace finger pricks?

No. The ADA says everyone using a CGM must have a finger prick meter available at all times.[3] NICE tells adults with type 2 diabetes on CGM that they will still need finger prick checks, though less often.[4]

Can I buy a sensor without a prescription?

In the US, yes. In March 2024 the FDA cleared the first over the counter CGM, the Dexcom Stelo, for adults aged 18 and over who do not use insulin. It has no alerts, so it is not for people who get problem low blood sugar.[12] We did not check the UK rules for buying a sensor without a prescription, so ask a pharmacist.

Does a diabetic patch deliver insulin?

A CGM sensor does not. It has three parts: a sensor under the skin, a transmitter and software on a phone or reader. It only measures glucose and holds no insulin and no medicine.[1] Insulin patch pumps are a separate prescription device, not a sticker.[3][13]

Where to go next

A diabetic patch, meaning a CGM sensor, gives you numbers to discuss with your care team alongside these related guides:

Note: If you are pregnant, breastfeeding, or considering giving any supplement or herbal product to a child, consult your healthcare provider before making any changes to your diet, supplement routine, or prescribed medications.

Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Talk to your doctor before changing your diet, your activity or your medicines, and before starting any supplement.

Sources & References

  1. National Institute of Diabetes and Digestive and Kidney Diseases (page last reviewed June 2023). Continuous Glucose Monitoring. US government institute page, written before 15 day sensors and over the counter sensors existed; Low Blood Glucose (Hypoglycemia) (last reviewed July 2021). Checked 25 October 2026. niddk.nih.gov
  2. NHS (pages last reviewed 14 October 2024 and 31 October 2024). Continuous glucose monitoring and hybrid closed loop for diabetes; Type 1 diabetes: living with; Low blood sugar (hypoglycaemia) (reviewed 3 August 2023). Checked 25 October 2026. nhs.uk
  3. American Diabetes Association Professional Practice Committee for Diabetes (2026). 7. Diabetes Technology: Standards of Care in Diabetes-2026. Diabetes Care. Committee disclosures are published separately by the ADA. pubmed.ncbi.nlm.nih.gov/41358889
  4. National Institute for Health and Care Excellence (2015, last updated 18 February 2026). Type 2 diabetes in adults: management (NG28), blood glucose management. The continuous glucose monitoring recommendations in section 1.7 are dated 2022. Checked 25 October 2026. nice.org.uk
  5. National Institute for Health and Care Excellence (2015, last updated 17 August 2022). Type 1 diabetes in adults: diagnosis and management (NG17), recommendations. Checked 25 October 2026. nice.org.uk
  6. Diabetes UK (technology page reviewed 2 October 2025; the flash page shows no review date). Flash glucose monitoring and continuous glucose monitoring; Can I get continuous glucose monitoring on the NHS?. Charity pages. The monthly cost is a charity estimate with no method shown. Checked 25 October 2026. diabetes.org.uk
  7. Jancev M, Vissers TACM, Visseren FLJ, et al. (2024). Continuous glucose monitoring in adults with type 2 diabetes: a systematic review and meta-analysis. Diabetologia. The authors say the work received no specific grant and declared no relationships that might bias it. pubmed.ncbi.nlm.nih.gov/38363342
  8. Martens T, Beck RW, Bailey R, et al.; MOBILE Study Group (2021). Effect of Continuous Glucose Monitoring on Glycemic Control in Patients With Type 2 Diabetes Treated With Basal Insulin: A Randomized Clinical Trial. JAMA. Study funding and study devices were provided by Dexcom Inc, which helped design the study. All authors reported Dexcom grants and one author is a Dexcom employee. pubmed.ncbi.nlm.nih.gov/34077499
  9. Alva S, Bhargava A, Bode B, et al. (2026). Accuracy of a 15-day Factory-Calibrated Continuous Glucose Monitoring System With Improved Sensor Design. Journal of Diabetes Science and Technology. Funded by Abbott Diabetes Care. Three authors are Abbott employees. pubmed.ncbi.nlm.nih.gov/40183340
  10. Basu A, Dube S, Veettil S, et al. (2015). Time lag of glucose from intravascular to interstitial compartment in type 1 diabetes. Journal of Diabetes Science and Technology. Six fasting adults with type 1 diabetes. One author was a consultant to Dexcom. Funding not stated in the PubMed record; full text not checked. pubmed.ncbi.nlm.nih.gov/25305282
  11. Garg SK, Kipnes M, Castorino K, et al. (2022). Accuracy and Safety of Dexcom G7 Continuous Glucose Monitoring in Adults with Diabetes. Diabetes Technology and Therapeutics. Supported by a grant from Dexcom, Inc. Four authors are Dexcom employees and stockholders. pubmed.ncbi.nlm.nih.gov/35157505
  12. U.S. Food and Drug Administration (news release 5 March 2024; meter page undated). FDA Clears First Over-the-Counter Continuous Glucose Monitor; Blood Glucose Monitoring Devices. US regulator pages. Checked 25 October 2026. fda.gov
  13. Lombardo F, Passanisi S, Tinti D, Messina MF, Salzano G, Rabbone I (2021). High Frequency of Dermatological Complications in Children and Adolescents with Type 1 Diabetes: A Web-Based Survey. Journal of Diabetes Science and Technology. The authors declared no conflicts of interest. Funding not stated in the PubMed record; full text not checked. pubmed.ncbi.nlm.nih.gov/32757778
  14. Herman A, Aerts O, Baeck M, et al. (2017). Allergic contact dermatitis caused by isobornyl acrylate in Freestyle Libre, a newly introduced glucose sensor. Contact Dermatitis. Case series of 15 patients using a 2017 sensor model. Funding and conflicts of interest not stated in the PubMed record; full text not checked. pubmed.ncbi.nlm.nih.gov/28804907
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