The measurement of blood glucose provides information on the effectiveness of blood glucose metabolism and guides interventions to achieve optimal glucose control within the body.

Diabetes can be managed by carefully monitoring some key indicators for each individual. NICE (NICE 2022) recommends that people with diabetes undertake nine annual health checks. It is vital that people with diabetes receive all nine of these key health tests and measures. These checks help to monitor and manage their condition as well as reduce the risk of complications such as stroke, heart disease and amputations.

The nine annual health checks for people with diabetes are:

• weight and body mass index measurements
• blood pressure
• smoking status
• blood test (HbA1c – blood glucose levels)
• urinary albumin test (or protein test to measure the kidney function)
• serum creatinine test (creatinine is an indicator for renal function)
• cholesterol levels
• eye check (retinopathy screening)
• foot check. (NICE 2022)

In addition to the nine annual health checks, Diabetes UK has identified 15 Healthcare Essentials. These have been highlighted so that people with diabetes and health care workers know what care people with diabetes should expect. These 'Healthcare Essentials' should also be undertaken annually or as required in the case of specialist care needs.

The '15 Healthcare Essentials' can be considered under four categories of:

• blood tests
• physical checks
• advice and support
• specialist care.

NICE guidelines for the UK currently recommend the following targets (the target blood glucose ranges below are indicated as a guide).

See: 

• NICE (2022a) Type 1 diabetes in adults: diagnosis and management
• NICE (2022b) Diabetes (Type 1 and 2) in children and young people diagnosis and management (Last updated 2023)

Children with Type 1 diabetes

• fasting plasma glucose level of 4–7 mmol/l on waking
• plasma glucose level of 4–7 mmol/l before meals at other times of the day
• plasma glucose level of 5–9 mmol/litre after meals (NICE 2022b).

Adults with Type 1 diabetes

• fasting plasma glucose level of 5–7 mmol/L on waking and
• plasma glucose level of 4–7 mmol/L before meals at other times of the day
• for adults who choose to test after meals, plasma glucose level of 5–9 mmol/L at least 90 minutes after eating (NICE 2022).

Type 2 diabetes (Diabetes UK Council of Healthcare Professionals 2015)**

• before meals: 4–7mmol/l
• two hours after meals: less than 8.5mmol/l.

Pregnant women with diabetes 

• fasting plasma glucose below 5.3 mmol/l
• plasma glucose level below 7.8 mmol/l 1 hour after meals
• plasma glucose level below 6.4 mmol/ l of 2 hours after a meal 

Pregnant women on insulin, should also be advised to keep their blood glucose above 4 mmol/litre, because of the risk of hypoglycaemia (NICE 2020).

When should blood glucose levels be measured?

The number of times per day the individual with diabetes should measure their blood glucose levels will vary from patient to patient depending entirely on their condition. The following is a useful general guideline however it doesn't apply to everyone and each case should be given individual advice.

Individuals with type 1 diabetes using insulin should check their blood glucose levels before every meal, sometimes as often as ten times per day.

Individuals with type 2 diabetes may measure their glucose levels if they are taking medications that can lead to hypoglycaemia (such as insulin and sulfonylurea). The frequency varies depending on the medication they are taking.

Individuals on Metformin and diet only, still may need to test their blood glucose periodically to observe trends in rising blood glucose.

Wearable glucose monitoring sensors

There are two types of continuous glucose monitoring (CGM) technologies; intermittently scanned flash glucose monitoring (isCGM) and real-time continuous glucose monitoring (rtCGM) which are described in this section. isCGM – Abbott Freestyle Libre and rtCGM Dexcom ONE are more commonly available in primary care.

CGM is available to any person living with type 1 diabetes based on their individual preferences, needs, characteristics and the functionality of the device. Shared decision making should be used to identify the most suitable device; if multiple devices meet their needs, the device with the lowest acquisition cost should be offered.

See this summary of available devices alongside guidance for initiation and support for CGM. 

Factors to consider when choosing a CGM device (NICE, 2022a):

• accuracy of the device
• whether the device provides predictive alerts or alarms and if these need to be shared with anyone else (for example, a carer)
• whether using the device requires access to particular technologies (such as a smartphone and up-to-date phone software)
• how easy the device is to use and take readings from, including for people with limited dexterity
• fear, frequency, awareness and severity of hypoglycaemia
• psychosocial factors
• the person's insulin regimen or type of insulin pump, if relevant (taking into account whether a particular device integrates with their pump as part of a hybrid closed loop or insulin suspend function)
• whether, how often, and how the device needs to be calibrated, and how easy it is for the person to do this themselves
• how data can be collected, compatibility of the device with other technology, and whether data can be shared with the person's healthcare provider to help inform treatment
• whether the device will affect the person's ability to do their job
• how unpredictable the person's activity and blood glucose levels are and whether erratic blood glucose is affecting their quality of life
• whether the person has situations when symptoms of hypoglycaemia cannot be communicated or can be confused (for example, during exercise)
• clinical factors that may make devices easier or harder to use
• frequency of sensor replacement
• sensitivities to the device, for example local skin reactions
• body image concerns.

In addition, people living with type 2 diabetes are eligible to receive CGM if they are on multiple daily insulin injections (2 or more per day) or:

• they have recurrent hypoglycaemia or severe hypoglycaemia
• hey have impaired hypoglycaemia awareness
• hey have a condition or disability (including a learning disability or cognitive impairment) that means they cannot self-monitor their blood glucose by capillary blood glucose monitoring but could use an isCGM device (or have it scanned for them)
• they would otherwise be advised to self-measure at least 8 times a day.

For guidance on continuous glucose monitoring (CGM) for pregnant women, see the NICE guideline on diabetes in pregnancy.

• 1.6.18 - Offer isCGM to adults with insulin-treated type 2 diabetes who would otherwise need help from a care worker or healthcare professional to monitor their blood glucose.
• 1.6.19 - Consider real-time continuous glucose monitoring (rtCGM) as an alternative to isCGM for adults with insulin-treated type 2 diabetes if it is available for the same or lower cost. (NICE 2022c)

Healthcare professionals who will be working with flash and continuous glucose monitoring are directed to these webinars. It is important you are able to help your patients access wearable glucose monitoring devices appropriately, interpret their data and improve their glycaemic outcomes.

Continuous Glucose Monitoring

Unlike finger-prick blood glucose testing, flash-is-CGM and rt-CGM measures a person’s interstitial glucose level. This means the glucose levels in the body tissues below the skin. Interstitial glucose levels lag behind capillary blood glucose by approximately 4.5-4.8 minutes (‘lag time’). This means that when blood glucose is changing rapidly the measurements will differ. For this reason during times of rapidly changing blood glucose levels such as hypoglycaemia patients and clinicians must revert to finger-prick testing.

How does it work

A sensor sits on the back of the arm with a probe just under the skin.

An overview of flash-isCGM

• Flash-isCGM requires an interstitial sensor and a receiver. The sensor is self-inserted into the upper arm and lasts up to 14 days. It is attached to the body with clinical adhesives. It transmits glucose data to a receiver when it is scanned. The receiver may be a handset or the user’s mobile phone and it stores and displays their data.

• By scanning or 'flashing' the sensor with a scanning device or mobile phone the person can observe:
  a) glucose level
  b) a graph of glucose level for the last 8 hours
  c) a direction or ‘trend’ arrow showing if levels are going up or down. The device also stores your data and makes it easy to view patterns over time.

• Various apps and software are available to present this data to the user and clinician using the cloud. They can then review and respond to glucose patterns.

• Interstitial glucose lags behind capillary blood glucose by 2.4 minutes (known as lag time). This means that when blood glucose is changing rapidly the measurements will differ. For this reason during episodes of hypoglycaemia patients and clinicians must revert to finger-prick testing.

• isGM (Libre2)  has an optional alarm connected via Bluetooth to warn the wearer if their blood glucose is going too low. Scanning is still required to see the actual blood glucose level and trend arrow.

Advantages of isCGM

• relatively painless insertion
• reduction in frequency of finger pricking
• easier to identify trends and improve control
• ability to test more regularly
• easier than finger-pricking in lots of situations (on transport, in rain, in cold, during sport)
• less social stigma than finger pricks
• modest impact on glucose monitoring costs for people with type 1 using intensive insulin regimes. Flash may even confer savings regarding potential reductions in severe hypogylcaemia
• some people preferred the arm as a location rather than stomach
• data can be downloaded for the user and clinician to view values and trends and uploaded for clinician review of ambulatory glucose profiles
• has been proven to improve HbA1c
• in 2019 the DVLA allowed the use of CGM as an alternative to finger prick testing to check blood glucose levels while driving provided glucose levels are >4.0mmol/l (if 4.0mmol/l or below a confirmatory finger prick is required.

Disadvantages of isCGM

• it can give inaccurate readings if blood glucose levels are changing rapidly
• must be scanned at least every 8 hours to provide an ambulatory blood glucose profile
• some users have reported reactions to the adhesive
• a finger prick blood glucose must still be used to check erroneous readings and also to manage control if symptoms do not match readings. 

An overview of rt-Continuous Glucose Monitoring

Real time continuous glucose monitoring (rtCGM) works in a similar way to intermittently scanned flash-isCGM with a sensor, transmitter and receiver as described above and can be worn on the arm / abdomen, or with some sensor buttocks in those under 17 years old. rt-CGM provides a constant stream of real time glucose data throughout the, day and night without the need for scanning. Lag time of rtCGM is approximately 4 -5 minutes depending on the device. 

Additional advantages of real-time CGM:

• rtCGM systems do not need to be scanned by the wearer. The glucose data is automatically transmitted to the handset/smart device and to the cloud in ‘real-time
• rtCGM systems have additional alarms which can be individualised to alert the person that they need to take action to adjust their blood glucose – the blood glucose level is displayed in real time alongside the alarm. 
• some rtCGM systems are licensed to link to an insulin pump and use the data to adjust some the persons insulin doses for them using an algorithm to enable a ‘closed loop’ system
• multiple sensor sites.

Disadvantages of rtCGM:

• phone compatibility can vary
• some users report alarm fatigue
• some users do not like being continually attached to technology
• some users do not trust the technology, and this can lead to overriding advise which can cause erratic glucose levels. 

Further resources

• Diabetes UK. Meds and Kit. Further information on wearable technologies
• Diabetes UK. Driving and diabetes. Further information on the law around using flash-GM and CGM for driving. See here: DVLA guide to insulin treated diabetes and driving
• Diabetes UK. Flash Glucose monitors
• Diabetes UK. Diabetes health checks (annual review)
• Diabetes UK. Know Your Risk of Type 2 diabetes
• Diabetes UK. Flash glucose monitors (Freestyle Libre) and continuous glucose monitors (CGM)
• Trend Diabetes. Trend Podcast Episode 4 – Glucose Sensor Technology Mixdown
• Trend Diabetes. Sensor Technology For Community Nurses: A Practical Toolkit
• Dexcom. Diabetes Education and CGM Research.
• RCN. CGM in Real Time Nursing Introduction to HCL

What is Diabetic ketoacidosis (DKA)

Diabetic ketoacidosis (DKA) is an acute medical emergency. It is mainly seen in people with T1DM however does occur in type 2 diabetes particularly when SGLT2 inhibitors are being taken. If an individual with diabetes has sustained high blood glucose readings, it is an indication that there is not have enough insulin in their system, or that the insulin that they have is not working properly.

When this happens, it is possible that their body will start breaking down fat and proteins in order to get energy for metabolic processes. As ketones build up in the body, a state of ketoacidosis occurs, or in diabetes, Diabetic Ketoacidosis (DKA). The body cannot function properly in a state of acidosis. The person may initially experience nausea, vomiting and fatigue. As symptoms progress the person may begin to exhibit deep and fast breathing, confusion and the breath may smell of pear drops or nail varnish. Normal levels of ketones are usually considered to be <0.6 and these levels may be seen in people without diabetes eg when fasting for long periods.

If the acidosis is not corrected, this may lead to coma and in rare cases, death. (Diabetes UK) See Diabetes and acute illness, sick day rules section.

Access to ketone testing is recommended for all individuals with type 1 diabetes. NICE (2020) recommends testing for ketones if fasting or premeal blood glucose levels become  unusually high - usually above 11 mmol/l for an unknown reason (such as illness, dehydration or abdominal pain). Ketone testing is also recommended for lower blood glucose if the person feels unwell.

• they forget or decide not to take their insulin
• they are unwell of injured
• they are using ‘flozin’ (SGLT2) tablets to manage their diabetes

Testing for ketones in this way can help detect the problem at an early stage. This allows for advice and treatment to be given before the level of ketones in the blood becomes dangerous.

Test for ketones if:

Type 1 diabetes - Premeal BG above 11 and showing signs of underlying illness

Type 2 diabetes - Taking a ‘flozin’ and showing signs of underlying infection

Signs of underlying illness include:

• raised temperature
• symptoms of virus
• symptoms of infection
• shortness of breath
• nausea and vomiting
• abdominal pain.

However local policies will vary and should be followed.

Ketones can be measured in two ways:

Urine - This involves dipping a urinalysis test strip in urine and the strip changes colour depending on the amount of ketones detected. It is usually recorded as +, ++, +++ or ++++.

A result of 2+ or more mans there is a high chance of DKA.

Blood – This involves a finger prick and using a blood ketone meter (similar to a blood glucose meter).

Blood Ketone Levels:

< 0.6mmol/l = normal

0.6-1.5 mmol/l - slightly increased risk of DKA – test again in 2 hours

1.6-2.9 mmol/l - increased risk of DKA – contact GP / Diabetes team ASAP

3 mmol/l or more - very high risk of DKA – immediate medical help required.

(Breakthrough T1D, 2025)

Blood ketone testing is considered more accurate because the level of ketones in urine reflects the length of time the urine has been in the bladder.

Urine ketone testing is cheaper. Urine ketone testing might be preferred when a person does not want to have to do another finger prick, for example if they are testing for ketones very frequently.

How to perform a ketone test

1. Assemble the required equipment to perform the urinalysis

3. Check the urine sample is fresh - observe the colour and odour. Cloudy urine may indicate the sample is contaminated or infection is present. A strong fishy smell may indicate infection and a sweet odour like pear drop sweet may indicate ketones are present.

4. Check the sample is from the correct person and note any medications they are taking (as some medications may affect the result).

5. Wash hands and apply gloves/apron.

6. Remove a test strip from the bottle and replace the lid.

7. Immerse the full length of the test strip in the urine sample, ensuring all the test pads are covered. Remove excess urine on the lip of the sample bottle.

8. Place the test strip on the tissue/absorbent paper to prevent the colours on the pads contaminating each other.

9. Start the timer/note the time.

10. Replace the lid on the urine specimen.

11. When the appropriate amount of time has passed, align the test pads with the corresponding result gauge on the test strip bottle.

12. Be sure to line the pads up with the corresponding test on the container. This is where most errors with urine testing are made!

13. Remove your glove and record the result of the urine test in the person’s medical record. Report any abnormal result to a senior nurse, the diabetes care team or the person’s doctor as appropriate to your role and care setting.

14. Dispose of all equipment in the clinical waste bag.

15. Wash your hands.

Each individual with diabetes in entitled to an 'annual review'.

The following will usually be discussed at the annual review:

• medical history and general health
• medication review
• specific needs or cultural preferences may be discussed
• advice and support, including details about support groups
• offering an educational course regarding the management of diabetes
• diet and lifestyle advice
• blood pressure monitoring
• blood glucose monitoring
• HbA1c check and agreeing individualised
• explaining about the symptoms, risks and treatment of hypos
• discussing cardiovascular disease and risk
• ensuring annual retinal screening is completed
• foot checks
• checking for other long-term complications that can be caused by diabetes, such as problems with your kidneys or nerves
• pregnancy should be discussed (if appropriate) including information about contraception and family planning.

Further resources

• NICE (2015, updated 2022) Type 2 diabetes in adults: management

Diabetes Prevention Programme

Many cases of Type 2 diabetes are preventable and there is strong international evidence that behavioural interventions can significantly reduce the risk of developing the condition, through reducing weight, increasing physical activity and improving the diet of those at high risk. To help reduce the risk of developing Type 2 diabetes, the Diabetes Prevention Programme has been developed.

Individuals eligible for inclusion have ‘non-diabetic hyperglycaemia’ (NDH), defined as having an HbA1c 42 – 47 mmol/mol (6.0 – 6.4%) or a fasting plasma glucose (FPG) of 5.5 – 6.9 mmol/l. The blood result indicating NDH must be within the last 12 months to be eligible for referral and only the most recent blood reading can be used. Only individuals aged 18 years or over are eligible for the intervention. 

Further resources

• NHS England. NHS Diabetes Prevention Programme (NHS DPP)

Overview of Continuous Glucose Monitoring in the management of diabetes 

Continuous Glucose Monitoring (CGM) is a technology that continuously tracks and estimates your blood glucose levels (blood sugar) throughout the day and night.  

The device consists of a small sensor with a filament inserted under the skin, usually on the abdomen or back of the arm. This measures glucose levels in the interstitial fluid and sends and displays readings directly to an individual’s phone or digital device.  

CGM plays a crucial role in the management of diabetes. By providing instant glucose monitoring, individuals can spot trends and patterns and have more control over their levels.  

Who can use a CGM?

The use of CGM is used against the following criteria: 

1. Anyone with type 1 diabetes. 

2. People with type 2 diabetes who receive multiple daily injections of insulin in the following circumstances:

• episodes of frequent, recurrent hypoglycaemia occurring each week or month that have an impact on quality of life
• having had more than one episode a year of severe hypoglycaemia (where they were unable to take oral treatments) with no preventable precipitating cause (Continuation criteria - a sustained reduction in severe hypoglycaemic episodes.)
• having an impaired awareness of hypoglycaemia (≥4 on the Gold or MMCHS scale)
• have a condition or disability (including a learning disability or cognitive impairment) that means they cannot self-monitor their blood glucose by capillary blood glucose monitoring
• would otherwise be advised to self-measure at least 8 times a day.  

3. Pregnant women with type 2 diabetes treated with insulin who have:  

• problematic severe hypoglycaemia (with or without impaired awareness of hypoglycaemia) or  
• unstable blood glucose which is causing concern despite efforts to optimise glycaemic control (12 months in total inclusive of postdelivery period).  

4. People treated with insulin who would otherwise need help from a care worker or health care professional to monitor blood glucose.  

5. Real time continuous glucose monitoring (rtCGM) in those children and young people with type 2 diabetes who are on insulin therapy. Consider intermittently scanned continuous glucose monitoring (isCGM), commonly referred to as 'flash', for children and young people with type 2 diabetes aged 4 years and over who are on insulin therapy if:   

• rtCGM is contraindicated for them or 
• they express a clear preference for isCGM (with a reader).  

6. People with other forms of diabetes:  

• type 3c diabetes who are on insulin therapy, for example, cystic fibrosis-associated diabetes 
• people living with any form of diabetes who are on haemodialysis and insulin treatment. 

Other requirements include:  

• use of shared decision-making tool to support device choice 
• if multiple devices meet the needs and preferences, the device with the lowest cost should be offered 
• education on CGM has been provided (online or in person) 
• agree to use a CGM sensor more than 70% of the time and collect at least 70% of data 
• agree to regular reviews with the local clinical team.  

Therefore, the use of CGM must meet these criteria and depend on local policy and pathways in primary and secondary care. 

For more information and to read the NICE guidance Type 1 diabetes in adults: diagnosis and management.

Benefits of using a CGM 

CGMs have been found to improve the quality of life for people with diabetes. The benefits of using a CGM in diabetes management include: 

1. Instant (‘real-time’) glucose monitoring: CGM provides continuous readings, allowing individuals with diabetes to monitor their glucose levels without the need for fingerstick blood tests. This information can help people make decisions about insulin dosing, diet and physical activity.   

2. Detection of glucose trends: CGM devices not only provide current glucose readings, but also track trends in glucose levels over a period of time. Users can see whether their glucose levels are rising, falling or stable, enabling them to anticipate and respond to potential hyperglycaemic (‘hypo’) events. 

3. Alerts and alarms: CGM systems can be programmed to provide customisable alerts and alarms. These alerts notify users of hypo episodes, allowing them to make decisions that can prevent any complications.   

4. Insight into glucose patterns: By analysing CGM data, individuals can gain insights into their glucose patterns, including patterns related to meals, physical activity, and sleep. This information can help with diabetes management strategies and adjusting treatment plans accordingly.   

5. Integration with insulin pumps: Many CGM systems are compatible with insulin pumps, enabling automated insulin delivery through closed-loop systems. This integration allows for more precise insulin dosing based on instant glucose data, leading to improved glycaemic management and a reduced risk of hypoglycaemia.   

6. Remote monitoring and data sharing: CGM devices often feature remote monitoring capabilities, allowing caregivers or health care providers to remotely access glucose data and provide support and guidance as needed. Data sharing functionalities enable users to share their glucose data with their health care team for remote monitoring and phone consultations.   
7. Improvement in glycaemic management: Clinical studies have shown that CGM use is associated with improvements in glycaemic management, as proved by reductions in HbA1c levels and a decrease in the time spent in hypo/hyperglycaemic ranges. These improvements contribute to better long-term outcomes and reduced risk of diabetes-related complications.  

Examples of sensors used in diabetes management

All CGMs estimate blood glucose levels, but how they store and display data can be different. For example: 

1. Glucose Sensors for Continuous Glucose Monitoring (CGM) 

Dexcom One, G6 and *G7 
 
This is a popular CGM system that consists of a small sensor inserted under the skin, which continuously measures glucose levels in the interstitial fluid. The sensor provides instant glucose readings and trend data to the individual’s phone or device. *Dexcom G7 can only be used with the hybrid close loop system (HCL). 

Abbott FreeStyle Libre 2  
 
This is a CGM system that uses a small sensor worn on the back of the upper arm to measure interstitial glucose levels. Users can scan the sensor with a reader (flash) or phone to get instant glucose readings without the need for fingerstick blood tests. Please be aware that Libre 3 can only be used with the hybrid close loop system (HCL). 

2. Insulin Pump Sensors 

Medtronic MiniMed 780g connected to a Guardian 4 sensor 

This is an insulin pump system that works with CGM technology to provide automated insulin delivery. The system uses sensor data to adjust basal insulin delivery rates and minimise both low and high blood sugar events.  

Tandem t:slim X2 control IQ 

This is an insulin pump system that features predictive low glucose suspend (PLGS) technology and automatic correction boluses. It uses CGM data (when used as hybrid close loop with Dexcom G6 or G7 sensors) to suspend insulin delivery when glucose levels are predicted to reach a low threshold, which reduces the risk of hypoglycaemia.  

Omnipod 5 with Dexcom G6 

This is a patch pump hybrid closed loop system that uses a predictive algorithm to adjust basal settings and continuously adjust user needs over time. From summer 2024, this is expected to connect to Libre 2 Plus. 

These are just a few examples of the sensors used in diabetes management. There are many other devices (glucometers, smartpens) and technologies (apps) available. These all play important roles in helping individuals with diabetes monitor their glucose levels, manage their insulin therapy and lead healthier lives.