Continuous glucose monitoring for type 1 diabetes management

One of the latest technologies used in diabetes management is continuous glucose monitoring (CGM), which – as the name suggests – allows people to monitor their glucose automatically. It is important for general practice nurses to be aware of solutions that can help patients manage and control their condition

WHAT IS TYPE 1 DIABETES?

Diabetes mellitus is a metabolic disorder characterised by the body’s inability to control levels of glucose in the blood. Type 1 diabetes (T1D) accounts for around 8% of cases in the UK.¹ It occurs when the pancreas doesn’t make any insulin at all. The body breaks down carbohydrates into glucose, but in diabetes, insufficient or ineffective insulin – or the complete absence of it – means the body is unable to use the glucose as it should. Therefore, glucose is not able to enter the target cells where it should be used for energy production, and instead accumulates in the bloodstream and the interstitial space.

Over time, excessively high glucose levels (hyperglycaemia) may cause potentially serious complications, including diabetic retinopathy, nephropathy, neuropathy, foot disease and damage, cardiovascular disease, and sexual dysfunction.²

T1D can affect people of any age. It used to be commonly referred to as ‘juvenile-onset’ or ‘early-onset’ diabetes. However, T1D can also begin in adulthood, so this misnomer has been largely abandoned.³ With the introduction of GAD antibody testing there has been an improvement in diagnosis and increased understanding that it occurs at any age.

Type 2 diabetes is caused due to insulin insufficiency and can be controlled by diet and exercise, oral and parenteral medication. However, because T1D is an auto-immune disease leading to a destruction of the pancreatic cells, daily insulin therapy is the only treatment.

SYMPTOMS OF TYPE 1 DIABETES

The symptoms of both type 1 and type 2 diabetes are similar, but in type 1, they normally manifest rapidly over a period of days or weeks. In adults with type 2 diabetes, symptoms develop more slowly. Regardless of the precise diagnosis, the main symptoms are the same:

• Excessive thirst
• Urinary frequency and nocturia
• Bedwetting (in children)
• Genital itching/candidiasis
• Extreme tiredness and fatigue
• Sudden or unexplained weight loss
• Slow-healing wounds
• Blurred vision

If symptoms are ignored, and as glucose cannot be used by the body cells, the body begins to break down fatty acids to use for energy. This leads to the synthesis of ketones, an acidic by-product of the body burning its own fat. Ketones are normal and safe at a low level, but in people with diabetes (more commonly, type 1), levels can become dangerously high and result in a life-threatening condition called diabetic ketoacidosis (DKA),⁴ requiring immediate medical attention. This can itself be a symptom of undiagnosed type 1 diabetes, and can cause additional symptoms, such as:

• Dehydration
• Vomiting
• Rapid heartbeat and tachycardia
• Confusion/disorientation
• Heavily laboured breathing/ hyperventilation
• Unusual-smelling breath (often a fruity or sweet smell)
• Loss of consciousness

DKA rates at diagnosis are falling, however it is still woefully common and continues to contribute to 0.16% of type 1 diabetes deaths per year.⁵ According to the 2017 National Paediatric Diabetes Audit, nearly a quarter (23%) of newly diagnosed children and adolescents are hospitalised with DKA due to delayed diagnosis.⁶ Among adults, hospital admissions for DKA increased between 1998 and 2007, then plateaued until 2013, with around 4% of adults with T1D having an episode of DKA each year and around 6% of total cases occurring in people who are newly diagnosed.⁷

MISDIAGNOSIS

Since there is a clear risk of DKA and other complications, particularly if diabetes goes unrecognised, it’s crucial that the disease is diagnosed promptly. However, lack of awareness of T1D makes misdiagnosis a real possibility. This can, in part, be attributed to the fact type 1 is comparatively uncommon. Of the 4.7 million people in the UK with diabetes, just 8% have type 1.

A 2018 study found that 20% of adults who developed type 1 diabetes over the age of 30 were wrongly identified as having type 2 diabetes initially, and later diagnosed with type 1.⁸ Participants were tested for levels of C-peptide, a substance released by the pancreas alongside insulin, the measurement of which is indicative of diabetes types – where higher levels suggest type 2 and lower levels, type 1.

The tendency towards a diagnosis of type 2 is understandable: it is markedly more common in adults than type 1, and the symptoms bear a striking resemblance to one another. Yet, while recognising that rapid weight loss, a low body mass index (BMI), and an onset age of younger than 50 go hand-in-hand with type 1, NICE recommends that health care professionals ‘do not discount a diagnosis of type 1 diabetes if an adult presents with a BMI of 25 kg/m2 or above, or is aged 50 years or older’.⁹

DIAGNOSTIC TESTING

NICE guidance suggests a diagnosis of T1D in adult patients under the age of 50 who present with hyperglycaemia, typically backed up by ketosis, rapid weight loss, BMI of 25 kg/m2 or lower, and a personal or family history of autoimmune disease.³ The World Health Organization (WHO) 2006 diagnostic criteria, endorsed by Diabetes UK, recommends the following tests.¹⁰

• Random blood glucose test, where a concentration of 11.1 mmol/l or above indicates diabetes
• Fasting blood glucose test, where a concentration of 7.0 mmol/l or above indicates diabetes
• Blood glucose test two hours after an oral glucose tolerance test (OGTT), where a concentration of 11.1 mmol/l or above two hours after 75g anhydrous glucose in an OGTT indicates diabetes
• HbA1c > 48 mmol/mol (6.5%).

NICE also recommends that adults with suspected T1D who exhibit atypical symptoms – being overweight, over 50 and with slow-evolving (rather than rapid-onset) hyperglycaemia, for example – be considered for C-peptide testing and/or screening for diabetes-specific autoantibodies GADs.¹¹

In children – and adults – health care professionals should bear in mind symptoms (think ‘4 Ts’ – toilet, thirsty, tired and thinner) and confirm a diagnosis of type 1 diabetes using the blood glucose testing outlined in the WHO’s criteria. Children should be referred immediately to a specialist paediatric team.¹²

TREATING TYPE 1 – ADVANCES IN TECHNOLOGY

The primary and essential treatment for type 1 diabetes is insulin therapy.¹³ Insulin can be taken as regular injected doses (multiple daily injections [MDI]), or by continuous subcutaneous insulin infusion (CSII), commonly known as insulin pump therapy.

Since the 1960s, the primary tool people with diabetes have used to measure their glucose levels is a blood glucose meter or BGM.¹⁴ BGMs require a patient to prick their finger with a needle and place the resulting drop of blood onto a test strip that is read by the meter. The meter then reveals a single value that represents the patient’s glucose level at that exact moment in time.

Checking glucose more regularly can help people gain better handle on their levels, enabling them to adjust their treatment as needed, and thereby help them reduce frequency or occurrence of hypoglycaemia (low glucose levels) and hyperglycaemia (high glucose levels) – acute complications of both insulin diabetes therapy and some oral antidiabetic drugs.¹⁵

It is suggested that people are more likely to achieve good control of their T1D if they check their glucose at least four times a day.¹⁶ In fact, many living with diabetes are increasingly turning towards innovative technologies that make regularly checking glucose levels easier and more discrete. BGM alternatives on the market in recent years have included flash glucose monitoring Flash and continuous glucose monitoring (CGM). While on the surface BGM, Flash and CGM may seem to be the same, there are important differences between the three options.

WHAT IS CONTINUOUS GLUCOSE MONITORING?

Continuous glucose monitoring (CGM) checks the amount of glucose in the interstitial fluid surrounding the body’s cells. A small sensor is inserted into the skin and connects to a transmitter that sits on the surface of the skin, which is held in place by a sticky plaster similar to the type used to secure a cannula in place.

The transmitter is wirelessly connected either to a smartphone, or to a receiver, which records and displays the glucose measurements either in real time or retrospectively. In addition, the real-time CGM is able to provide automatically alarms and alerts, even warning the user 20 minutes in advance of onset of hypoglycaemia. Software enables users to download the readings and see patterns in their glucose levels over time, or at certain times – for example before or after eating. Real-time continuous glucose monitoring (RT-CGM) is proven to reduce HbA1c while decreasing time spent in hypoglycaemia – and patients experience these benefits regardless of delivery method.¹⁷ Unlike a blood glucose meter, which provides just a single reading, RT-CGM provides continuous, dynamic real-time information about a user's glucose levels. With readings up to every five minutes – up to 288 readings a day – patients will know where their glucose is headed and how fast it's getting there. Flash, which also measures interstitial fluid, requires the patient to scan a sensor placed on the arm in order to receive a glucose reading but does not provide alerts and alarms.

In a randomised clinical trial of 161 adults with T1D, glycaemic control was improved during CGM use compared with conventional treatment (HbA1c 63 vs 68 mmol/mol [7.92% vs 8.35%]). The mean difference in HbA1c was 0.43% (4.7 mmol/mol). This means CGM may result in better glycaemic control compared with conventional treatment, but further research is needed to assess clinical outcomes and longer-term adverse effects.¹⁸ Additionally, in a different randomised clinical trial, using Dexcom CGM reduced the average number of hypo events in MDI patients by 72% from the baseline.¹⁹

CGM is proven to be effective in helping diabetes patients better manage their diabetes, regardless of whether they use a pump or – as is the case for most adult patients with T1D – MDI for insulin delivery.²⁰ A study comparing the effectiveness of CGM vs. self-monitoring of blood glucose BGM in adults with T1D on MDI insulin therapy, found significant A1C reduction in the CGM group.²¹

A number of studies have also demonstrated superior glucose control and the avoidance of hypoglycaemia in people using RT-CGM and are treated with multiple daily insulin injections.^22-25 This evidence supports recommendations that RT-CGM should be made widely available to patients with T1D, and further suggests that the best outcomes are achieved when people wear the device continuously, rather than intermittently.

CONTINUOUS GLUCOSE MONITORING ON THE NHS

RT-CGM should not be offered routinely for adults with type 1 diabetes, according to NICE,11 but clinicians should consider RT-CGM for adults who are willing to commit to using it at least 70% of the time and to calibrate it as needed, and who have any of the following despite optimised use of insulin therapy and conventional blood glucose monitoring:11

• More than 1 episode a year of severe hypoglycaemia with no obviously preventable precipitating cause
• Complete loss of awareness of hypoglycaemia
• Frequent (more than 2 episodes a week) asymptomatic hypoglycaemia that is causing problems with daily activities
• Extreme fear of hypoglycaemia
• Hyperglycaemia (HbA1c level of 75 mmol/mol [9%] or higher) that persists despite testing at least 10 times a day. Continue real-time continuous glucose monitoring only if HbA1c can be sustained at or below 53 mmol/mol (7%) and/or there has been a fall in HbA1c of 27 mmol/mol (2.5%) or more.

However, NICE does recommend offering alarmed RT-CGM to children under the age of 18 with T1D who experience frequent severe hypoglycaemia, experience lack of hypo awareness with associated problems, or who are unable to identify the symptoms of hypos.¹²

RT-CGM should also be considered for children and young people under the age of 18 who take part in high-level sport and exercise, and those who have comorbidities or take medication (such as corticosteroids) that can impair glucose control.¹²

In 2016, NICE reviewed the use of integrated sensor-augmented pump therapy systems for managing glucose levels in patients with T1D. These systems combine continuous glucose monitoring with continuous subcutaneous insulin pump therapy, to inform about interstitial glucose levels up to every five minutes, allowing users to deliver adjusted insulin doses, immediately and in real time.

CONCLUSION

CGM technology is constantly evolving, so it’s critically important for healthcare professionals to keep up to date with the latest innovations and features, especially because not all CGM technology is the same. Advancements in RT-CGM systems are becoming increasingly user-friendly. For example, the number of days patients can wear a sensor without changing it has increased. Some CGM devices have eliminated the need for finger prick tests, however if your glucose alerts and readings from the device do not match symptoms or expectations, a conventional blood glucose meter should be used to confirm diabetes treatment decisions. CGM devices are also compatible with some Apple and Android smart phones and watches. The latest versions can be used in children as young as two years old.

NICE is currently reviewing its clinical guidelines for diagnosing and managing T1D in adults, and both type 1 and type 2 diabetes in children and young people. The review will consider whether any new evidence is likely to impact current clinical guidelines. Additionally, it is examining whether existing guidance on NHS availability of integrated sensor-augmented pump therapy systems for people with type 1 diabetes should be updated.

With the pace of change in technology, it is only a matter of time before people with T1D have greater choice of devices to optimally manage their condition. Not only that, but there is hope that more systems will be funded by the NHS for more patients, improving outcomes for patients.

Declaration

This promotional feature was initiated by Dexcom, who have reviewed the article for accuracy but had no influence on the content.

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