How can we build on A1C? Looking at metrics that can help with daily glycemic control

For nearly 50 years, the hemoglobin A1C test has been the go-to metric for evaluating glycemic management.¹ But with wearable diabetes tech like continuous glucose monitors (CGMs) becoming more mainstream, patients and providers no longer have to wait months until the next A1C test to see how well their diabetes management plan is working. There are a lot of newer tech-enabled metrics that patients and providers can use to help inform their diabetes management decisions. 

What metrics, in addition to A1C testing, can people look at to engage with their diabetes management? How can providers help their patients understand this data? To explore these questions and more, we talked with Amy Tenderich, a technology journalist and prominent patient advocate who lives with type 1 diabetes, and Amy Hess-Fischl, an award-winning diabetes care and education specialist. Amy Tenderich and Amy Hess-Fischl both received a fee from Novo Nordisk for their participation.

Before we talk about some of the other metrics also being used today, let’s talk about A1C. How useful is it for patients and providers?

Well, the A1C test is still helpful in that it gives you an average measure of your blood glucose levels over the past 2 to 3 months.² It’s still the most recognized metric in clinical settings to assess glycemic control,³ and it’s a simple way to evaluate the clinical trial results of different diabetes therapies at a high level.⁴

But here’s the thing about averages: they’re more useful when you’re considering long-term trends. I personally don’t go more than 20 minutes at a time without thinking about my diabetes. In any of those individual moments, I don’t always think about my 3-month average. I think about my present, about how I’m feeling and what my glucose levels are right now. I might average 60 miles an hour on the freeway, but if I were to hit 100 miles an hour, there could be consequences. I need both the long-term and short-term trends to know how I’m truly doing with my diabetes management.

Fortunately, there are other metrics now that will tell me how my glucose levels are doing on a day-to-day basis, and a lot of them are enabled by my CGM.

As a provider, an A1C test is a useful metric for me to quickly gauge how a patient is doing overall. I can’t envision a world anytime soon where it gets replaced. Like Amy T said, it’s still the primary metric used for making decisions on overall glucose management and assessing the risk of long-term complications associated with diabetes. That’s on a global scale, too—there are many communities in other parts of the world where CGM adoption has been relatively low, and therefore won’t have access to CGM-enabled metrics.^2,5

It is also worth noting that measurements like time-in-range (TIR), time-below-range (TBR), time-above-range (TAR), and the glucose management indicator (GMI) are recognized as useful in clinical settings by the American Diabetes Association because they may provide insights for a more personalized diabetes management plan.⁶ The target "range" for TIR is between 70-180 mg/dL for many patients with type 1 or type 2 diabetes, and when patients spend 70% of their time there, that correlates to an A1C of about 7%.⁷

So, A1C is still a useful big-picture metric, and we now have other ways to evaluate and course correct glycemic management between A1C tests.

Still, as a provider, I do recognize that the A1C test can feel challenging for patients. I’ve seen how people can attach a lot of emotion to the numbers they see, and when you look at the data from the T1D exchange in 2016-2018, many children, adolescents, and adults did not achieve an A1C goal <7.5%.⁸ So when I’m working with patients, it’s my job to deconstruct those numbers for each person to see how we can move the needle.

And, now that we have access to them through newer technology, I can't help but want to layer on additional metrics that can help me and my patients get a clearer picture of how they are doing with their glucose levels day to day and even hour to hour.

OK, let’s talk about some of those other metrics. Which newer diabetes metrics can help people engage with their daily management?

Within the patient community, there has been a big push, known as the Beyond A1C movement, to drive awareness and adoption of TIR as a key tool for assessing glycemic control each day. TIR is just one of several metrics included on the ambulatory glucose profile (AGP) report.⁹ In contrast to A1C results, looking at TIR data from an AGP report can help offer people with diabetes actionable insights into the changes in their glucose levels moment to moment.⁷ I think the A1C feels like an exam you can often fail without understanding why. TIR is useful in the immediate term and can be easy to understand for those of us living with this condition.

Again, this is possible thanks to the proliferation of CGMs, and that’s given the movement a lot of momentum in recent years. Someone wearing a CGM can essentially check their glucose in real time, either on their device or in a compatible app on their phone.¹⁰ People can see for themselves which way they’re trending and what percentage of time they’re staying within their target blood glucose range. 

When you’re able to look at your glucose that way, on your own or with your provider, it allows you to ask questions like, “What can I work on to get into that target range more consistently?” For me, I might look at the app that my CGM connects to and say, “Wow, my TIR is better on Tuesdays and Thursdays, what’s going on there? Oh, right, those are the days when I work out.” 

My provider and I periodically go over this report together, trying to map changes in my routine to fluctuations in my data so we can decide together what the best response might be. I recommend that everyone wearing a CGM does this with their provider. 

I love me some AGP. The AGP is a one-page report that summarizes the last 14-90 days, depending on the time frame chosen, of a person’s glucose data.^9,11 It’s a great tool to have on hand when giving someone a snapshot about how their glucose management is going. 

In addition to TIR, I can also sit down and talk through someone’s TAR or TBR. Amy T, I think what’s great about your example with your workout days is that it shows how empowering it can be to have this data on hand. For people who are consistently hitting their target range, we can identify and reinforce good habits. If someone is having trouble staying in range, maybe our conversations will help them find a way to make an adjustment in their routine that pushes them closer to their goal. Again, it’s about moving the needle.

The AGP report also includes the GMI, which is calculated based on a person’s average glucose levels over that 14-, 30-, 60-, or 90-day period and tries to assess their glucose management on a broader scale. (We used to call this estimated A1C, or eA1C, but people found that name confusing.)^11,12  In combination with the other metrics on the report, this is another way providers can try to identify trends in a person’s glycemic control.

Tech delivers: From detailed data come meaningful metrics^11-14

With access to technology rising, people with diabetes can have more data at their fingertips than ever. What should providers emphasize when recommending these devices to patients?

Whether we’re talking about the AGP report or any of these metrics that tech is letting us see more consistently, it’s important to level set—the data you get is only as good as that person’s device usage. An individual needs to be wearing a CGM for at least 70% of the time over 14 days to generate useful data.⁹

So yes, tech can help empower people to look at their data and do something about it, but first they have to be willing to wear the tech. I work with a lot of people with diabetes, type 1 and type 2, younger and older, who aren’t as engaged with their care as they could be. I think a lot of the time it’s because they don’t know how.

With my teenage and young adult patients in particular, a lot of them don’t want to wear a CGM all the time, so I have to negotiate. “Can we start with 2 weeks, just so we can look at the report and see what there is to see?” If that works, then they can get a taste of what tech has to offer.

And as providers, I think we owe it to ourselves to keep initiating these conversations. The more success we have educating people about tech and getting them interested enough to do a trial run, the better we will become at making those recommendations in the first place. When we find out what works and doesn’t work for some people, we can be quicker to recognize what might help someone else.

It’s worth mentioning that while we’ve focused a lot on the data that CGMs can provide, there are some people who wear a smart insulin pump or use a connected insulin pen without a CGM. For those people, there’s still a lot of value in automatically logging their insulin doses and having that data at a glance. And actually, there are some people calling for the standardization of digital insulin data, which could yield something similar to the AGP report but for tracking insulin distribution.¹⁵

In general, I would say that capturing data in the previous era was a lot more haphazard. You got the reading from sticking your finger several times a day, and then you had to log all of that data and all of your insulin doses manually. Compare that to now where some devices have their own software that can generate a version of your AGP report on the fly.¹⁶

One CGM I like can send you a weekly TIR report, which is nice for offering reminders and reinforcement. It also has a feature that can tell me what my best day was in the last week, so I like to look at that and compare it to my calendar to see what I can carry over into my daily routine. That ability to reflect on my health habits and double down on what’s working is what I find really encouraging, and the tech makes that possible.

For people who are trying to become more engaged in their diabetes care, the breadth of available metrics can be overwhelming. What can providers do to help patients navigate their data?

The primary care providers I work with get about 15-20 minutes to talk to their patients. That’s not a lot of time to talk to someone about diabetes data, let alone other possible issues, so you have to make the most of it.

Each patient is different, so I try to make sure I am taking an individualized approach to every appointment. I know I could spend as little as 5 minutes digging into an AGP report, or I could spend upwards of 30 minutes, depending on how much time we have and what is important to them. 

I would encourage my fellow providers to make it a habit of asking patients what they want to focus on. Then you can confidently sit down and say, “Let’s focus on TIR today—how do we address some of these spikes?”

Health care providers can help people with diabetes engage with their care by drawing connections between their data and their daily habits.¹⁰

I think for patients to be better oriented with their data, providers also need to be prepared to engage with it. Not everyone gets to see an endocrinologist or a certified diabetes care and education specialist (CDCES) like Amy H. A 2021 survey of 303 health care providers showed that only 56% of primary care providers were aware of TIR, and only 67% were familiar with the standardized CGM metrics for clinical care.¹⁷

To Amy H’s point, the AGP report can definitely be a lot to get through, which is why some researchers have been working on a single number to summarize it. In 2022, a group of clinicians proposed a new metric called the glycemia risk index (GRI), which compares a person’s risk of hypo- and hyperglycemia and rates their overall management on a scale from 0-100.¹⁸

One of the points of this new measurement is that somebody can have good TIR but still too much TBR or TAR. So, we’ve been talking about going beyond A1C, but now some people are saying we should go beyond TIR. The GRI could make it simpler for providers to assess multiple CGM reports.¹⁸ It remains to be seen whether GRI will catch on, but it’s always encouraging to know that the diabetes community is continuing to push for better ways to talk to each other about diabetes.