Blood Glucose Monitoring: An In-depth Guide

Blood Glucose Monitoring: An In-depth Guide

If you have recently been diagnosed with diabetes, you may want to know more about blood glucose monitoring — such as what it is, how it works, and the different types of glucose monitoring devices. 

Find out more about blood glucose monitoring in our guide below.

What is blood glucose monitoring, and why is it important?

When you live with diabetes, regular glucose monitoring is essential to help you manage your blood glucose levels, maintain your health and reduce your risk of the long-term complications of diabetes [1].

Too high or low blood glucose levels can cause long-term and short-term complications that may affect your current and future health and may even be life-threatening [2]. 

Blood glucose monitoring is the process of checking how much glucose is in your blood to ensure your levels don’t get too high or too low [3].

Regular blood glucose monitoring will help you learn how your food, exercise, illness and stress impact your glucose levels, so you can work with your healthcare professionals to adjust your treatment, make changes to your dietary habits and actively manage your diabetes with confidence [2, 3].

Continuous glucose monitoring (CGM)

Continuous glucose monitoring, or CGM, is an innovative way of checking your blood glucose around the clock [3]. An implanted device (which uses a tiny sensor inserted under the skin) automatically tests your glucose levels continuously day and night, even when you’re sleeping [2, 3, 4]. 

The sensor sends the glucose readings via a transmitter to a receiver (either a device or an app on your phone) so that you see real-time glucose levels, identify glucose patterns and spot highs and lows [2, 3, 4]. Many CGM devices can send alarms or alerts if they detect problems such as hypoglycaemia [2].

The device measures the glucose in your interstitial fluid (the fluid that surrounds the cells in your body) rather than your blood glucose levels [2, 4]. There is a slight delay between glucose changes in this interstitial fluid and your bloodstream, so your CGM glucose reading may differ from a finger-prick result [2, 4]. This means CGM measures may not always be a reliable indicator of rapidly changing blood glucose levels. You will need to finger-prick to calibrate the device and make important decisions about your diabetes management [1, 4].

Another disadvantage of CGM is that sensors and machines can be relatively expensive, limiting access to these life-changing devices to those who receive funding through their medical aid or can fund it themselves, making them a less viable option for those who don’t have subsidised health care/medical aid [2]. 

However, research shows that CGM improves traditional self-monitoring [4]. Using a continuous glucose monitoring device can improve your diabetes management by — reducing your risk of hypoglycaemia or hyperglycaemia, reducing your Hba1c and subsequently reducing your risk of long-term complications [4]. 

Flash glucose monitoring

Flash glucose monitoring (FGM) is sometimes known as intermittently scanned continuous glucose monitoring (isCGM) [6, 7]. 

Similarly to CGM, flash glucose monitors measure your glucose levels without pricking your finger — using a small sensor implanted just under your skin, which scans the glucose levels in the fluid around your cells  [7]. This is worn for up to 14 days [7].

However, unlike a CGM, the flash monitor doesn’t continuously measure and display glucose readings [7]. Instead, you only get readings on demand when intermittently scanning your sensor [6, 7].

Flash glucose monitoring devices are generally considered to have good accuracy, and studies show that they can improve diabetes management and quality of life while reducing the risk of diabetes-related complications [7]. They also represent a cheaper and valid alternative for some people with diabetes, where appropriate [7].

However, flash devices have some disadvantages — they are not generally as accurate as newer CGM devices and cannot connect to an insulin pump [7]. Unlike many CGM systems, they don’t typically warn about hypo- or hyperglycaemia [7]. Nevertheless, monitoring technology is evolving quickly, and alarms are being added to newer flash models [6, 7].

Types of blood glucose testing

Traditionally, blood glucose testing has consisted of two different types of tests: self-monitoring blood glucose levels (SMBG) — which you would do at home, yourself — and blood tests to measure your glycated haemoglobin (HbA1c), which are done by a healthcare professional [1, 2].

Below is how both types of blood glucose testing work and what they do. 

Self-monitoring of blood glucose levels (SMBG)

Self-monitoring of blood glucose levels involves regular finger-prick testing (several times a day), then using a home-testing kit to measure the blood glucose at that instant in time [3]. 

Testing your blood glucose like this can be done at home or when you’re out and about, without any professional help — your diabetes care team will teach you how to carry out the test and act on the results [3].

Following a structured self-monitoring regime can help you improve your diabetes management and keep your glucose levels as close to normal as possible when you’re living with type 1 or type 2 diabetes [3]. However, periodic testing only provides a snapshot of your blood glucose; it can't identify problems in between finger-pricks or predict impending episodes of hypoglycaemia [1].

HbA1c testing

HbA1c testing (or glycated haemoglobin testing) is a blood test that indicates your average blood glucose levels over the previous two to three months [3]. 

Your healthcare professional or diabetes care team will arrange the test every three to six months to monitor your glycaemi ccontrol [3]. The target for most people living with type 1 diabetes is 48 mmol/mol (6.5%) or lower — but your healthcare professionals will individualise your target according to your diabetes and your needs [3].

The HbA1c test is recommended to assess glycaemic control and predict your risk of developing complications [4]. 

However, it has some limitations; it only gives an average of your glucose levels and doesn’t detect rapid changes, such as high or low glucose episodes and hyperglycaemia after eating [1, 4]. In addition, the test can be unreliable if you have certain conditions such as anaemia or haemoglobinopathies (genetic blood disorders) or are pregnant. It may also be affected by genetics or ethnicity [1, 4].

Types of blood glucose monitoring (and devices)

For people living with diabetes, regular glucose testing can be an uncomfortable and unpleasant lifetime commitment [5]. However, new technologies provide more effective and comfortable monitoring and managing blood glucose levels twenty-four hours a day [1, 3, 5].

Blood glucose monitoring — in particular, continuous glucose monitoring (CGM) — provides a convenient, comprehensive assessment of blood glucose levels and can help improve management  [4].  

Different glucose monitoring devices are available to people with diabetes [4, 5]. Below, we discuss these three options for blood glucose monitoring in more detail.

Closed-loop technology (artificial pancreas)

Used correctly, a hybrid closed-loop is the most advanced system available for insulin delivery for people living with diabetes [8]. 

Sometimes known as an artificial pancreas, hybrid closed-loop systems use a computer algorithm to take glucose readings from a continuous glucose monitor, calculate the dose of insulin required and administer the insulin through an insulin pump [8, 9].

The closed-loop system automatically adjusts the background rate of insulin whenever your blood glucose becomes too low or too high [9]. It works continuously — even when you’re sleeping — repeating the loop cycle at regular intervals every 5-12 minutes (depending on the system used) [9]. 

Scientific studies have demonstrated that hybrid closed-loop systems appear well-tolerated — improving glucose management, reducing the risk of hypos, improving quality of life and reducing the burden of managing type 1 diabetes [8, 9].

However, hybrid closed-loop systems take work and do have disadvantages. You will still have to count carbohydrates in your foods and programme extra insulin doses at mealtimes [9]. Exercise, alcohol, high carbohydrate and high-fat meals remain challenging to manage even with hybrid closed-loop systems, so management strategies must be tailored to your individual needs [9]. Training and support from healthcare professionals are needed to ensure the best results from these devices [9].

Who could benefit from blood glucose monitoring?

Many people living with diabetes could benefit from blood glucose monitoring using one of the above methods. The reduced painful finger-pricking, improved diabetes management, and reduced frequency of dangerous episodes of hypoglycaemia can improve the health and well-being of users [4, 6, 7, 8, 9].