NICE guidance - continuous glucose monitoring (CGM) in type 2 diabetes

Continuous glucose monitoring (CGM)

• offer intermittently scanned continuous glucose monitoring *(isCGM, commonly referred to as 'flash') to adults with type 2 diabetes on multiple daily insulin injections** if any of the following apply:
  • they have recurrent hypoglycaemia**** or severe hypoglycaemia ***
  • they have impaired hypoglycaemia awareness
  • they 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
    
    
• 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
• 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
• CGM should be provided by a team with expertise in its use, as part of supporting people to self-manage their diabetes
• advise adults with type 2 diabetes who are using CGM that they will still need to take capillary blood glucose measurements (although they can do this less often). Explain that is because:
  • they will need to use capillary blood glucose measurements to check the accuracy of their CGM device
  • they will need capillary blood glucose monitoring as a back-up (for example when their blood glucose levels are changing quickly or if the device stops working)
  • provide them with enough test strips to take capillary blood glucose measurements as needed.

* continuous glucose monitoring

• covers both real-time continuous glucose monitoring (rtCGM) and intermittently scanned continuous glucose monitoring (isCGM, commonly referred to as 'flash')
• a continuous glucose monitor is a device that measures blood glucose levels and sends the readings to a display device or smartphone

** multiple daily insulin injections

• two or more daily insulin injections, which could either be a basal-bolus regimen or more than one daily insulin injection

*** severe hypoglycaemia

• episodes of hypoglycaemia that require assistance from another person to treat

**** recurrent hypoglycaemia

• frequent events of hypoglycaemia that occur each week or month and have an impact on quality of life

NICE committee (1):

• agreed that people with impaired hypoglycaemic awareness would also benefit from isCGM. However, they did not recommend specific methods for assessing impaired hypoglycaemic awareness
  • is because validated methods for assessing impaired hypoglycaemic awareness in people with type 2 diabetes (such as the GOLD or Clarke scores) are not always available in primary care
• noted that people who use insulin and have a condition or disability that restricts their ability to self-monitor blood glucose levels should also be offered isCGM
• noted that people who need help from a care worker or other healthcare professional to administer their insulin injections should also be offered isCGM, even if they only use once-daily insulin injections

Notes:

• subcutaneous continuous glucose monitoring (CGM)
  • has proven benefit in type 1 diabetes (2)
    • various designs (3,4)
      • subcutaneous monitoring
        • involves the subcutaneous insertion of a glucose sensor attached to a transmitter that sends signals to either an insulin pump or a hand-held meter
        • worn for 7 days
        • sensor inserted into subcutaneous abdominal fat
        • devices generally require regular calibration and blood glucose testing about twice a day
        • subcutaneous glucose levels change more slowly than plasma glucose, and this may be an important limitation, particularly if glucose levels are changing rapidly
          • subcutaneous glucose levels, therefore, have a short time lag, compared with blood glucose measurements, and measurements may not always match blood glucose. Nevertheless, when worn regularly (changed every 7 days), they improve outcomes in terms of hypoglycaemia and hyperglycaemia
          • patients can be alerted to hypo - and hyperglycaemia, and take early action to correct blood glucose levels
        • some CGM devices if used with particular insulin pumps will shut the pump off if a low glucose level is identified and thus is designed to prevent hypoglycaemia
          
          
      • a non-invasive CGM device uses the principle of Raman spectroscopy where a painless pulse of monochromatic light is transmitted into the skin, and the scattered light is detected for the determination of glucose levels (4)
        • device can be worn on the abdomen like a band and measures blood glucose levels every five minutes
        • sensor transmits data to a smartphone which is also enabled with alarms during periods of glucose excursion
          
          
• flash glucose monitoring (FGM)
  • FreeStyle Libre, is the first FGM system - note that FGM technology is sometimes referred to as intermittent continuous glucose monitoring (iCGM)
    • uses a wired glucose oxidase enzyme co-immobilized on an electrochemical sensor that is worn on the arm for up to 14 days (5)
      • patch sensor is about the size of a coin and has a short filament (4 mm long) that must be inserted into the subcutaneous tissue of the upper arm
      • FGM system does not require calibration with patient's SMBG
      • availability of glucose data is only on demand; in FGM, the glucose values are not constantly shown, and people can obtain real-time interstitial glucose values by placing a "reader" in proximity to the sensor
      • data are transferred from the sensor to the reader and recorded automatically every 15 min
        • also trends for the previous 8 h can be seen on the screen
      • the glucose change trend is indicated using an arrow
        • there are no alarms (in contrast to CGM) when defined values are exceeded or expected to be exceeded in the following minutes
      • FGM lacks connectivity with CSII devices
      • glucose values, which can be downloaded at any time, are presented in a simple form and include the Ambulatory Glucose Profile (AGP), which combines all the data from the sensor over a period of 14 days and gives a summarized visual display of glycaemic patterns
      • FGM is accurate, with reported overall mean absolute relative difference (MARD) of 11.4% for sensor results and stable over 14 days of use when compared with capillary BG reference values, and unaffected by body mass index, age, type of DM, clinical site, insulin administration, or A1C (5)
      • use of FGM has been associated with improvement in glucose control in both uncontrolled T2 and T1DM, and maintained for up to 24 weeks of using the device (5)
        • in well-controlled patients with T1DM, the use of FCGM reduced the time spent in hypoglycaemia by 38% at 6 months (intervention group) versus controls (SMBG) (5)

Reference:

• NICE (March 2022). Type 2 diabetes in adults: management
• Yeh HC, Brown TT, Maruthur N, et al. Comparative effectiveness and safety of methods of insulin delivery and glucose monitoring for diabetes mellitus: a systematic review and meta-analysis. Ann Intern Med 2012;157:336-47
• Cohen N. Continuous glucose monitoring and pumps.Aust Fam Physician. 2015 May;44(5):284-7.
• yandres O, Yuen JM, Shah NC, VanDuyne RP, Walsh JT, Glucksberg MR. Progress toward an in vivo surface-enhanced Raman spectroscopy glucose sensor. Diabetes Technol Ther. 2008;10:257-265.
• Wright, L.A.-C.; Hirsch, I.B. Metrics beyond hemoglobin A1C in diabetes management: Time in range, hypoglycaemia, and other parameters. Diabetes Technol. Ther. 2017, 19, S16-S26