Storytime: Gareth’s Perspective on HbA1c and Time In Range

Many patients living with type 1 diabetes have been taught for a long time that HbA1c readings are the gold standard of understanding diabetes management¹. However, recently a new player has entered the game – a metric known as time in range (TIR), which has been made possible with the development of continuous glucose monitoring (CGM). Studies have shown TID is linked to diabetic complications in a similar way to HbA1c². Gareth, who has lived with type 1 diabetes for over 30 years, explains the logic behind the shift from HbA1c to TIR.

A Hard Sell

For over 30 years, everyone involved in the management of type 1 diabetes has asserted that a blood glucose (BG) level of 5.5mmol/L (100mg/dL) is the ultimate in perfection. So, of course it’s going to be a hard sell to understand why some diabetes healthcare teams are now talking about a soft target of 6.7mmol/L (120mg/dL). To understand this, we first need to go back to basics by taking another look at TIR and HbA1c.

Firstly, let’s look at these two metrics: HbA1c and TIR.

• HbA1c
  This is the blood test that looks at the 3-month average BG levels and traditionally has been equated with how well we’ve been managing our diabetes. It’s similar to having one piece of a jigsaw puzzle. However, this reading doesn’t consider the highs and lows that may still be happening every day, meaning that it may not be a reliable indicator of glucose management for many people living with type 1 diabetes¹.
• TIR
  This refers to the percentage of time that someone living with type 1 diabetes spends within a given blood glucose range, commonly between 3.9-10mmol/L (70-180mg/dL).¹ The CGM technology that we now have access to allows us to see daily patterns and fluctuations in our BG, providing the data to calculate TIR.

From diagnosis, I was always told that if my level was between 5-10mmol/L (90-180mg/dL) then I will minimise the chance of complications in the future. However, it was difficult to really see how long I was within that range by using random snapshots from manual BG tests. Now that CGM technology reads our BG levels every 5 minutes, we have access to extremely valuable information that determines how our management is truly going.

Technology Makes A Move

There are now automated insulin delivery systems available that emphasise TIR over the magic 5.5mmol/L (100mg/dL) number. These pumps utilise an algorithm to keep you within a range, minimising highs and, more importantly, lows.

It is now understood that hypoglycaemia can have a significant effect on the health and function of the brain³. I know that as I have been recovering from the dangerous lows, I can sometimes go hours with a fog over my brain and thoughts. This is not only scary in the short-term, but also for long-term implications. One of the limitations of HbA1c testing is that it does not offer information about low BG events. ¹

With a simple glance at my pump, now I have access to a graph summary that shows me the average amount of time spent within my given range, as well as the amount of time spent below or above it. The pump can also display the details of a single day or patterns over the month. This data is invaluable when tracking progress after making treatment changes.

As your pump gets to know you and your patterns, it tries to keep its readings around your personal target (often set around 6.7mmol/L) by giving micro boluses in a live setting, depending on the live data from the CGM. Every 5 minutes the algorithm uses the CGM data to determine how much insulin is needed to keep you within a range to minimise the risk of highs and lows. However, technology is rarely perfect, and there is still the chance of slipping above or below range. Live and learn from this is what I say!

Final Thoughts

Often, I see someone living with type 1 diabetes wondering if an automated insulin pump could fit into their life. After spending my first 16 years on multiple daily injections, making the move to pumps and CGM has changed my life. Now that new technology and a focus on TIR is upon us, I am excited for what the future holds and how blood glucose management will be revolutionised for those living with type 1 diabetes.

References

1. Beck RW, Bergenstal RM, Cheng P, et al. The Relationships Between Time in Range, Hyperglycemia Metrics, and HbA1c. Journal of Diabetes Science and Technology. 2019;13(4):614-626.
2. Vigersky R, McMahon C. The Relationship of Hemoglobin A1C to Time-in-Range in Patients with Diabetes. Diabetes Technology & Therapeutics. 2019; 21(2): 81-85.
3. Gejl M, Gjedde A, Brock B. et al. Effects of hypoglycaemia on working memory and regional cerebral blood flow in type 1 diabetes: a randomised, crossover trial. Diabetologia. 2018.61: 551–561 (2018).

This patient testimonial relates to an account of an individual’s response to treatment. The account is genuine, typical and documented. The views and opinions expressed are those of the patient or author and not representative of Medtronic or of any third parties referenced. The response other persons have to treatment could be different. Please speak with your diabetes healthcare team for information on whether the treatment is appropriate for you. The information provided in this blog is an individual account specific to the writer’s experience in the management of their own diabetes. Before considering any changes to your diabetes management you must speak with your diabetes healthcare team.

*Editor’s note: This article has been adapted and reproduced from a post published on Medtronic Diabetes Australia.