Continuous interstitial glucose sensing
- the standard of care in diabetes in T1DM and in some T2DM
The current standard of care for glucose monitoring in people with diabetes is still in many patients self-monitoring of blood glucose (SMBG) using blood glucose test strips and meters. Frequent glucose monitoring 4-10 times a day is a prerequisite for tight glycaemic control, especially for people with diabetes on intensive insulin therapy.
Glucose sensing technology has now developed to move beyond SMBG as the standard of care in T1DM and in some T2DM. This has been recognised by the Swedish National Board of Health (Socialstyrelsen) and the Finnish Medical Society Duodecim updated guidelines for diabetes, which in 2018 recommends that people with type 1 diabetes and recurrent hypo- or hyperglycaemia should be offered continuous glucose monitoring (CGM).
We still need good blood glucose test strips and meters with high precision to be used when the glucose level is very high or low, also when there is a technical or digital problem with the CGM system. Most T2DM people still use blood glucose test strips.
This new recommendation about CGM has been given the highest priority in the Swedish guidelines and this issue is also robustly taken up in the Finnish guidelines. We strongly support its on-going implementation in Finland and Sweden.
Even when performed frequently, intermittent blood glucose (BG) testing provides only a limited snapshot of BG levels without any trends or alarms. Glucose fluctuations between the tests are ignored and the estimation of the bolus dose of insulin before the meal is accordingly repetitively a really difficult task to manage. The reality is also associated to inconvenience and pain, and that´s why many patients avoid frequent SMBG tests.
isCGM and rtCGM
CGM technologies use a sensor to measure glucose levels in the interstitial fluid and provide a glucose data every 5 min. Two types of CGM systems are currently available: real-time CGM (rtCGM) and intermittently scanned CGM (isCGM}.
Each of these systems provide information about current and previous glucose levels over the course of the entire day, as well as using visual trend arrows to identify the direction and rate of glucose change and anticipated short-term future glycaemic status. isCGM provides this information when the user actively scans the sensor with the device reader or via an app on their smartphone, whereas rtCGM actively transmits this information without user engagement.
In each case they enable users to make immediate treatment adjustments to avoid unwanted high or low glucose. They can also review their data with a diabetes healthcare professional to target long-term improvements in glycaemic control, including minimizing time in hypoglycaemia, optimizing time in range, normoglycemia and also reducing the day-to-day glucose variability. All these parameters are strongly associated with each other and at the same time play an essential role in the quality of life in people with diabetes.
This is why isCGM and rtCGM systems is the standard of care for people on insulin therapy, since the evidence shows that hypoglycaemia and glycaemic variability are both important risk factors for diabetes morbidity and mortality independent from HbA1c.
isCGM and rtCGM systems are able to provide objective measurements for each element of the so-called ‘triangle of diabetes care’ that enable goals to be set for these important glycaemic indicators, also for showing Time In Range (TIR 4-8 (10) mmol/l, in per cent or hours per day) and for estimated HbA1c.
Both iCGM and rtCGM have the possibility of online data sharing with near relatives or health care providers by a smartphone. This may be especially important for a parent with a child with type 1 diabetes or for a solitaire adult person with type 1 diabetes.
The significant extra with iCGM and rtCGM
The cost of SMBG test strips is lower than that of rtCGM and isCGM systems. isCGM is about 1/3 of the price for rtCGM.
The benefits for improved glycaemic control are important for prevention of complication. isCGM has the benefit of being factory calibrated, whereas rtCGM systems require the user to perform daily calibration with SMBG. The exception here is the Dexcom G6 rtCGM system which can be calibrated with a scan code.
isCGM using the FreeStyle Libre system is approved in the EU and US for insulin dosing without the need for an adjunct fingerprick blood test, as are the Dexcom G5 and G6 rtCGM systems. CGM systems also differ in that rtCGM incorporates real-time notifications or alarms that alert users to low and high glucose, whereas isCGM does not.
The value of alarms is a topic of discussion, as so-called ‘alarm fatigue’ is reported to be a reason for patients discontinuing with rtCGM systems, albeit the alarm-functions can also been turned off for a needed period of time. The alarm function of rtCGM systems is more suited to groups of people with diabetes at higher risk of hypoglycaemia, such as those with impaired awareness of hypoglycaemia (IAH), young children and diabetes during pregnancy and also to those with high variability of daily glucose.
The decision and choice of the type of glucose sensoring system is based on the estimated need of the invidual person with diabetes. More comparative studies are needed and are coming.
The standard of care today for people with diabetes on insulin is the glucose sensoring technology.
Markku Saraheimo, MD, DMSc, debuty chief
Polyclinic of Internal Medicine of Helsinki City SOTE
Stig Attvall, MD, Ph D, assoc prof
Diabetes, Sahlgrenska University, Gothenburg, Sweden
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