CGM (Continuous Glucose Monitoring)

What is CGM?

CGM is known as Continuous Glucose Monitoring. It is a small device that is worn just under the skin where sensors are placed in the body but not directly in the blood stream. Despite the name the sensors measure the glucose present in your interstitial fluid (ISF), which is the fluid in and around the body’s cells and not blood glucose.

The relationship between glucose concentration in ISF and blood could allow for 288 glucose level readings a day without having to do finger prick tests. As a result, CGM is a less invasive technique for measuring blood glucose levels. It can be used with a pump or injections. It operates 24 hours a day and can include alarms to indicate when glucose levels are too high or low.

CGM is different to finger prick testing because your blood glucose levels are measured every few minutes, continuously throughout the day and night. As a result, you can identify trends in your levels which can alert you to highs and lows. Over time, you will be able to acquire a graph of your blood glucose levels.

Types of CGM

  • Real Time – You can check your blood glucose levels yourself at any time, as well as being able to download them.
  • Retrospective – You can’t see your glucose levels in real time, but you can look back at results by downloading them.

Information from CGM is 5 to 15 minutes older than the reading from a finger prick test. None of the CGM systems that are currently available are intended to be used in place of fingerpick testing. CGM simply acts as an extra layer of information.

How does CGM Work?

There are different parts that form CGMs:

  • Sensor – this sits just underneath your skin and measures your glucose levels by monitoring the interstitial fluid.
  • Transmitter – which is attached to the sensor and sends your blood glucose levels to your display device.
  • Display device – shows blood glucose levels. It might be a separate hand-held device (a stand-alone CGM) or a pump (an integrated system).

CGM devices come with software that allows you to analyse your results and see patterns in your blood sugar levels. Generally, you need to wear a sensor for up to seven days, after this time, it will need to be changed. When changing the sensor, you reattach the transmitter to your new sensor.

Advantages of CGM

The advantages of a CGM are:

  • You can track your blood sugar levels throughout the day and night.
  • You are able to see what your levels are like at times when you don’t normally test, such as during the night.
  • Trends can be identified; therefore, you can see when your glucose levels increase and decrease, and you can act quickly.
  • The need for finger prick tests is reduced.
  • HbA1c levels are improved as you tailor your insulin doses more carefully.
  • There is a reduction in the number of hypoglycaemic episodes that occur, because a downward trend can be identified before you actually experience a hypo.
  • You can set an alarm for when your blood glucose levels become too low or too high.

Disadvantages of CGM

The disadvantages of a CGM are:

  • You can become overloaded with data which can be confusing or worrying, especially if you don’t fully know how to interpret that information.
  • You may still need some finger prick checks.
  • You may find wearing the sensor irritating or unsightly.
  • You have to be motivated to use the data because it is the best form of diabetes management.

Acquiring and Funding CGM

A CGM can be purchased for around £1,000 for a standalone system. If you already have a pump and want an integrated system, that can cost approx. £500. Sensors will cost a further £60 each.

CGMs are expensive, so always ask a healthcare professional if you qualify for NHS funding. The National Institution for Clinical Excellence (NICE) has certain guidelines for people who could be eligible for CGM. Adults with type 1 diabetes could receive funding from the NHS if they meet the following criteria:

  • If one or more severe hypo occurs without any obvious, preventable cause.
  • There is complete loss of hypo awareness.
  • Repeat episodes of problematic hypos occur without any symptoms.
  • If there is an extreme fear of hypoglycaemia that is causing distress.
  • Inability to achieve a HbA1c of under 75 mmol/mol (9%), despite testing blood sugar levels at least ten times per day.
  • The intended user of CGM is willing to commit to using CGM at least 70% of the time and will keep it well calibrated.
  • The intended user of CGM is on daily insulin injections or uses an insulin pump.
  • The healthcare team providing the CGM has the experience and expertise to give advice on effective use of CGM.

There are also guidelines covering children who have type 1 diabetes. They could also be eligible if they are experiencing the following:

  • Frequent and severe hypoglycaemic episodes.
  • Hypo unawareness is resulting in seizures or anxiety.
  • Inability to recognise the symptoms of a hypo or adequately communicate them in order to prompt treatment.

Pregnant women may also be eligible for CGM if:

  • Problematic and severe hypos occur regularly.
  • CGM would improve poor glucose control.
  • CGM can provide useful information towards minimising too high or too low blood glucose levels.

NICE states that CGM devices could be made more widely available if it can be proved that it is effective in improving blood glucose control, reducing episodes of hypoglycaemia and demonstrates cost-effectiveness.