Time in Range vs. A1c: How Diabetes Technology Has Changed Healthcare

For years, the HbA1c test has been the gold standard of care for assessing a person's blood sugar levels over the previous three months. First developed in 1968 by Samuel Rahbar, MD, PhD, it wasn't actually available to the general public until the early 90s.

For many of us with diabetes, the HbA1c (also known simply as "A1c") meant check-ups every three months with our healthcare provider.

"A1c is based on a person's red blood cell turnover (the lifespan of a red blood cell) and the quantity of sugar attached to each cell," explains Diatribe . The higher your blood sugar levels are, the more sugar (or glucose) there will be on your red blood cells. But more recent understandings of A1c results point out that it can easily convey an inaccurate picture of blood sugar levels and overall diabetes management.

"Certain conditions, such as kidney disease, hemoglobin variants, certain types of anemia, and certain drugs and vitamins, impact red blood cell turnover, leading to misleading A1c values ," adds Diatribe.

Until recently, an A1c test required a visit to the blood laboratory in the nearest clinic or hospital for a blood draw from a vein in your arm. Fortunately, thanks to developments in diabetes management technology, we can learn our A1c in minutes from a finger prick and a large blood drop at your doctor's office!

But with those developments in technology came a completely different method of assessing a person's blood sugar levels. This new assessment is referred to as "time in range."

What is "time in range"?

The concept of "time in range" exists thanks to continuous glucose monitoring (CGM) systems. Quite simply, it means the percentage of each day that a person's blood sugars are within their goal range.

For example, a goal range set in your CGM might be between 80 to 160 mg/dL or 90 to 180 mg/dL or even as tight as 70 to 140 mg/dL for a pregnant woman. By setting your "low" and "high" alerts at these specific numbers, your CGM system will provide a report of what percentage of the day your blood sugars have been within that goal range.

60 to 85 percent, for example, is a worthwhile goal for "time in range." Achieving 100 percent is unrealistic considering the many variables and complexities within daily diabetes management.

One of the best aspects of "time in range" is that it focuses on the positive, explains Ariela Nielson , a CDCES who's also lived with type 1 diabetes for over 23 years, diagnosed at 10 years old.

"Talking about 'time in range' switches the conversation to a more positive focus because you're looking at the successful portion of blood sugar levels, say 65 percent of the time you are in your goal range, versus an A1c result that highlights the negative."

Time in Range vs. A1c: The Pros & Cons of Each

Neither method of assessing a person's blood sugar levels is perfect -- each come with their own set of pros and cons. Let's take a closer look.

A1c: Pros

The greatest aspect of A1c testing is that it's easily available to most patients, whereas "time in range" requires access and willingness to use a CGM. Even without health insurance, the out-of-pocket costs for an A1c test are under $50 per test .

An A1c test is also largely effective for highlighting when a patient's overall blood sugar levels are constantly high. A1c results measuring in the highest levels, between 10 to 16 percent, indicate an obvious need for intervention with either increased medication doses or the introduction of a new medication.

A1c: Cons

An A1c result doesn't reveal the amount of fluctuation a person is experiencing on a daily basis. Instead, it's providing a median (or middle) blood sugar level, which means that within a blood sugar range of 35 to 300 mg/dL, the implied median is 132 mg/dL.

This A1c result could very easily mislead you and your healthcare team into thinking your current blood sugar management methods are working well for you, when in fact those severe fluctuations are exhaustion, dangerous, and threatening to your short and long-term wellbeing.

A1c results are also easily affected by variables like pregnancy, certain medications, and the last time you donated blood. All of these variables can cause you to turnover new red blood cells more quickly which could lead to false A1c results that appear lower than they actually are.

The A1c test offers a very broad, vague picture of a person's overall blood sugar levels. Which means your healthcare team can only make vague guesses at how to help you improve your blood sugar levels.

Time in Range: Pros

Not only does time in range provide a picture of significant blood sugar fluctuations throughout the day, it also tells you exactly where and when those unwanted fluctuations are happening.

"We can make very specific adjustments in your insulin doses based on CGM data," explains Nielson. "If we don't have that much data, we can't make those minor adjustments very effectively. Instead, it's a lot of guessing."

It also helps her grasp how her patient is likely feeling on a day-to-day basis by looking at the frequency of severe low and high blood sugars.

"If you have an A1c of 6.5 but your blood sugar is dropping down to 50 mg/dL regularly, you probably don't feel very well," explains Nielson. "By looking at time in range, I can really get a better idea of how a person is feeling. If your blood sugars are swinging high and low regularly, your energy level is probably really low. The A1c test is just too broad to see this."

"When I was on the closed-loop system, my A1c went up but I noticed a big difference in my energy level," adds Nielson. "That's something we can't capture without focusing on time in range."

Time in Range: Cons

The biggest challenge to using "time in range" as a tool in diabetes management is the fact that it truly does require CGM technology.

Despite how popular this technology has become, it's also relatively expensive compared to a traditional glucose meter. Long-term CGM use requires health insurance or financial assistance along with a diabetes healthcare team to help you interpret your CGM data.

Nielson reminds, too, there is an art to interpreting CGM data. Generally, your primary healthcare team isn't going to have enough experience in reviewing CGMS data to effectively pinpoint consistent fluctuations and their cause, which means you'd need an endocrinologist, diabetes educator, or pharmacist on your team to interpret CGM data and make helpful adjustments in the details of your diabetes management.

"You can't simply look at every fluctuation and make changes," explains Nielson.

Nielson adds that it's about looking carefully at blood sugar trends rather than just one or two days of random or explainable highs and lows. Underestimating the carbohydrate-count in something you ate or struggling with a kinked cannula can throw off your data but it doesn't mean insulin doses should be adjusted.

What if you don't want to wear a CGM?

Of course, many patients may not want to wear a CGM, but there are alternatives to help gather more blood sugar data.

"Diabetes is very personalized," says Sara Lasker, CDCES and health coach who's lived with type 1 diabetes for most of her life.

"As we all know, what works for one person may or may not work for another. If they choose not to wear a CGM, we would work together to find what would work for them. Is it more frequent blood glucose checks? Is it checking at different times of day that they are not normally used to? Is it having them do a blind test for a few days with the CGM available through their clinic to get a baseline for next steps? Is it looking at the different types of CGM technology and assessing it differently based on the size of the device?"

Lasker's point is simply that there are other options, but you may need to speak up and start the discussion.

What does "time in range" success look like?

Deciding on the appropriate "range" for you and your diabetes is a very personal decision that you should discuss with your healthcare team.

"From a personal level, there are so many pieces to diabetes management," explains Lasker. "For example, let's say my target goal is 80 to 160 mg/dL and I am only in range 55% of the time. However, looking more in-depth at my numbers, you notice 95% of the time my blood sugars are running in the 70 to 170 mg/dL range. I would still consider that good diabetes management."

"However, what if the data showed the reason I was only in range 55% of the time, with the same target goal, was because my blood sugars were running from 39 to 390 mg/dL? Then I would take a harder look to see what I can do to lessen that variability in my blood glucose numbers."

"Time in range" is one very helpful and valuable tool in assessing your current diabetes management, but it's part of a bigger picture.

"Overall, there's been a shift in how we look at and treat people with diabetes," adds Nielson.

"We no longer use scare-tactics, threatening diabetes complications. That's a hard thing to feel motivated by."

Instead, Nielson says diabetes healthcare professionals are looking at the bigger picture, too.

"We've shifted more to looking at the psychological impact of having a chronic disease that is so complicated and demanding as type 1 and type 2 diabetes. We're focusing more on the individual and the psychological impact of dealing with a chronic disease."

Diabetes is complicated, and it's affected by nearly every part of our day-to-day life, which means we can't just look at the blood sugar levels and A1c results but instead at the whole person who is living with it.