By Gerri Klein RN MScN (biography and disclosures)
What I did before
Before the times of COVID and the introduction of continuous glucose monitoring, as a nurse diabetes educator, I instructed patients living with diabetes to attend the lab between 2 to 4 times per year to have glycated hemoglobin (A1C) assessment. In addition, I recommend home blood glucose monitoring at various times throughout the day for all patients who live with diabetes. Patients on insulin were instructed to perform as many as 6 to 8 finger pokes per day, while those not on insulin were asked to do less.
What changed my practice
A1C assessment became the gold standard of care for Canadian citizens living with diabetes when Diabetes Canada (formerly known as the Canadian Diabetes Association) included this laboratory test in the first published clinical practice guidelines for the treatment of diabetes mellitus in 1992 (1). Although mentioned in the initial 1992 standards of care, the use of home blood glucose monitoring, using finger sticks with a lancing device was not widely accepted in the early part of that decade. In contrast, the 1998 Canadian standards of care promoted home blood glucose monitoring as an “essential” part of the treatment plan for those with type 1 diabetes, and “integral” for persons with type 2 diabetes treated with oral hypoglycemic agents when used in conjunction with regular A1C testing (2).
While widely used and relied upon, there are many pitfalls when using these glycemic measures to guide treatments (3; 4). Although literature states that A1C levels reflect blood glucose values over a three-month period, glycation of red blood cells within an immediate 30-day period prior to the blood test has a more significant effect on the A1C value than does glycosylation of red blood cells aged 90–120 days. As the A1C is an average of the person’s glycemic control, it could be hiding many hyperglycemic and hypoglycemic excursions. A1C testing has been found to be inaccurate in persons with low hemoglobin, or vitamin B-12 and folate deficiency anemias and for those with kidney disease; may not be reliable in pregnancy, and should not be used after a recent blood transfusion or for persons experiencing alcoholism. A1C results are affected by some medication consumption, such as Vitamin A and C, antibiotics such as penicillin or cephalosporins, and medications such as salicylates and opioids. A1C testing requires persons living with diabetes to attend a laboratory, a difficult task for the last several months during COVID lockdowns. Lastly, A1C does not provide sufficient information to adequately inform immediate/short-term treatment decisions (5).
When first introduced, home blood glucose meters (HBGM) made real-time monitoring, and therefore intensive management, possible for persons who live with diabetes. However, the information offered by these devices is painful to obtain due to the necessity of finger pricks and is narrow in scope. Many will not test enough times during the day to get a complete picture of the blood sugars in order to make fully informed treatment decisions (6). As well, HBGM readings give time-limited information on which to base decisions. Present blood sugar is given, but there is no indication about where the blood sugar has been, or where it is trending.
In the past decade, continuous glucose monitors have changed diabetes care. Real-time continuous glucose monitors (rtCGMs) use a sensor, applied to skin and worn for 10 to 14 days to assess interstitial fluid glucose 24-hours per day, 7 days a week. rtCGM sensors communicate with readers using Bluetooth technology as long as the sensor is within range of the reader. Intermittently scanned continuous glucose monitors (isCGMs) have a similar ability as the rtCGM, but require the user to swipe a reader across the sensor to obtain data. rtCGMs and some isCGMs have high/low alerts to notify users when their blood sugars are dangerously high or low, a valuable tool for those on hypoglycemic medication, particularly those with hypoglycemic unawareness. Due to the time that it takes for glucose to diffuse from blood into the interstitial fluids, the data offered by either type of CGM may not be as current as offered by an HBGM. CGM users are advised to confirm readings with an HBGM if physical symptoms do not coincide with the CGM data.
Recent updates in the Diabetes Canada clinical practice guidelines include recommendations for use of A1C assessments as well as rtCGMs and isCGMs (5). In the recently revised guidelines, 2021, A1C assessments are recommended every 3 months, “Grade D, Consensus level” of confidence. Diabetes Canada has given a “grade A, Level 1A” recommendation for rtCGM for persons living with type 1 diabetes to reduce A1C and increase TIR (time in range), and significantly reduce duration and incidence of hypoglycemia; and to improve quality of life. A “grade B, Level 2” recommendation has been given for isCGM to increase TIR, reduce frequency and duration of hypoglycemia, and improve treatment satisfaction.
CGM glucose metrics include TIR (time in range), TAR (time above range), TBR (time below range), as well as glycemic variability (standard deviation of readings). These metrics make it possible for healthcare providers to set individualized blood glucose targets for patients and to conveniently track the data.
Patients can download their data using a free, industry-supported app and email their data to healthcare providers prior to visits. If the volume of emails is a concern for practitioners, or if patients do not send their data when asked, healthcare providers can log into industry-supported pages for remote monitoring or discuss glucose control with patients during a visit. Day to day blood glucose graphs, along with the amount of time that blood glucose is within a specified target range, frequency and duration of hypo/hyperglycemic events, including timing of these events, standard deviation of blood sugar data, and glucose averages for times during the day are all available online, making it easier for healthcare providers to devise appropriate treatment plans. An estimated A1C is also provided.
What I do now
For all my patients who are on hypoglycemic medications, oral or injectable, I suggest using rtCGM or isCGM. Cost is a significant issue for many although the cost of these devices varies from pharmacy to pharmacy. BC Fair Pharmacare does cover the cost of some rtCGMs if the person has special authority (obtained by a physician and when the person is on two types of insulin or an insulin pump) and has paid their deductible. Other provincial pharmacare plans cover both rtCGMs and isCGMs for qualifying patients. For those without app-compatible phones, some companies provide readers free of charge with proof of sensor purchase. In BC, only rtCGMs are included on the Fair Pharmacare formulary and therefore if the person’s deductible is too high for Fair Pharmacare rtCGM coverage they must pay out of pocket. If unable, I suggest using an isCGM as these devices can give the same data as rtCGM at much less cost.
Even intermittent use or a short trial of 10 days to two weeks with either of these devices can be enlightening for patients. To get them started, I instruct my patients to contact companies directly, as frequently sample devices are offered at no cost. Some companies have compassionate care programs to supply sensors free of charge or at a reduced cost, physicians must apply to the company for patients to access these programs.
With the ongoing COVID restrictions, many of my patients have been unable (or unwilling) to obtain an A1C from a lab test. In my practice, I have found it helpful to use glucose TIR to assess glucose control as an adjunct measure to A1C results; when an A1C is not available; and to guide treatment recommendations. Treatment and goals can be customized to patients as TIR is determined by age, physical status, co-morbidities, length of time living with diabetes, living situation; and hypoglycemic awareness (5;6;7).
There have been momentous discoveries in diabetes care over the past 100 years that have improved the lives of those living with diabetes. I believe that the discovery of CGM is pivotal and will significantly change outcomes for many who live with the condition. As cost will be a barrier for many, it is beholden upon us as healthcare providers to lobby our provincial health ministries to make these devices available to all who are on hypoglycemic medication, particularly insulin, and in the future to anyone who lives with diabetes and needs to perform home glucose monitoring.
- Expert Committee of the Canadian Diabetes Advisory Board. Clinical practice guidelines for treatment of diabetes mellitus. CMAJ. 1992;147(5):697-712. (View)
- Zinman B, Lau D, Leiter L, Meltzer S, Daneman D, et al. 1998 clinical practice guidelines for the management of diabetes in Canada. CMAJ; 1998;159 Suppl 8(6): S1-29. (View)
- Radin M. Pitfalls in Hemoglobin A1c Measurement: When Results may be Misleading. J Gen Intern Med. 2014; 29(2): 388–394. DOI: 10.1007/s11606-013-2595-x. (View)
- Kaiafa G, Veneti S, Polychronopoulos G, et al. Is HbA1c an ideal biomarker of well-controlled diabetes? Postgrad Med J. 2021; 97(1148): 380–383. DOI: 10.1136/postgradmedj-2020-138756. (View)
- Diabetes Canada Clinical Practice Guidelines Expert Working Group: Cheng A, Feig D, Ho J, Siemens R. Blood Glucose Monitoring in Adults and Children with Diabetes: Update 2021. Can J Diabetes. 2021; 45(7); 580-587. DOI: 10.1016/j.jcjd.2021.07.003. (View)
- Holt R. et al. The management of type 1 diabetes in adults. A consensus report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASE). Diabetes Care. 2021; 64(12): 2609-2652. DOI: 10.2337/dci21-0043. (Request with CPSBC or view with UBC)
- Gabbay M, Rodacki M., Calliari L, et al. Time in range: a new parameter to evaluate blood glucose control in patients with diabetes. Diabetol Metab Syndr. 2020; 12(22). DOI: 10.1186/s13098-020-00529-z. (View)