People with diabetes learn quickly that it’s vital to keep a close eye on their blood sugar levels.
Technology continues to evolve to help people with diabetes monitor their blood sugar levels so that they can keep them in their target range. Continuous glucose monitors (CGM) are one type of technology that provides that kind of vital information.
Since the 1990s, the diabetes community has relied on the hemoglobin A1C to evaluate average glucose levels over the course of 3 months.
But with modern CGM technology, a newer metric known as the glucose management indicator (GMI) is helping some people with diabetes gain more insight into their glucose fluctuations — and helping them manage their diabetes better.
A key to life with diabetes is monitoring your blood sugar (glucose) levels.
High blood sugar levels can lead to potentially serious complications. Over time, high blood sugar levels can damage blood vessels that carry blood to your vital organs and lead to damage to your eyes, nerves, kidneys, and heart.
Very high blood sugar levels can also lead to a dangerous condition called diabetic ketoacidosis (DKA), which can lead to loss of consciousness, coma, or even death.
In the early days, people monitored their glucose levels by placing a test strip in their urine and comparing it to a color-coded chart.
Then, in the 1980s, home glucose meters became common. They used a fingerstick to check a drop of blood on a different kind of test strip.
But with the rise of CGM technology in the early 2000s, people with diabetes can now more continuously monitor their glucose levels and get a more complete picture of the trends in their diabetes management.
CGMs use a tiny sensor inserted under the top layer of skin. It measures the level of glucose in your interstitial fluid and transmits those readings every 1 to 5 minutes to a medical smartphone app or separate handheld device to see your glucose patterns in real-time.
That information can help you make adjustments throughout the day to keep your blood sugar levels within your target range.
You can see immediately when you experience a big jump or drop in blood sugar, and you can determine what led to those big spikes and dips. Did you eat something that sent your blood sugar levels soaring? Or did you exercise hard and send your blood sugar levels plummeting?
The advent of CGM technology means that you no longer have to rely on routine fingerstick tests. And since CGMs can take a reading about every 5 minutes and send the data to your smartphone or tablet, you can get hundreds of blood sugar readings per day.
This technology has been a game-changer for many people with diabetes. Research shows that CGM tech helps those with diabetes (especially type 1 diabetes) better manage their condition and overall health.
As CGM has become more common, people with diabetes have started using a measurement known as the GMI.
Your GMI is the average (mean) glucose value based on the data collected by your CGM. Here’s how to get your GMI.
You need the average glucose values from your CGM to get the GMI percentage:
GMI (%) = 3.31 + 0.02392 x [mean glucose in mg/dL].
For example, if your mean glucose level was 150 mg/dL, your GMI would be 6.9% ( 51.9 mmol/mol ).
The GMI is not the same as the A1C.
An A1C test measures your blood sugar levels over the past 3 months, so your A1C level reflects the average over that long time period.
More specifically, this kind of test gauges the amount of blood sugar, or blood glucose, attached to the hemoglobin in your red blood cells.
Why 3 months? That’s the average life span of a red blood cell.
Typically, the higher your A1C, the higher your blood sugar levels you may have. For most people with diabetes, the recommended A1C level is 7% or below — although the specific number will vary and is best determined with your diabetes care team.
For many years, A1C was considered the go-to option for glycemic control. In fact, the landmark Diabetes Complications and Control Trial (DCCT) in 1993 established A1C as the gold standard.
However, advances in diabetes technology have revealed that A1C isn’t as reliable as once thought. The #BeyondA1C movement took shape in the latter half of the 2010s, and the GMI was recognized as the better measurement.
Leading diabetes experts have determined that previous term “estimated A1C” (or eA1C) wasn’t helpful because people with diabetes might assume that it’s comparable to their 3-month A1C results.
Also, A1C does not reveal episodes of hypoglycemia or hyperglycemia, and research indicates that it can be skewed based on high or low blood sugars prior to an A1C lab test being performed.
In 2018, a team of researchers found that GMI was a better indicator of someone’s estimated glucose trends over time.
Although their study found that 51% of people only saw an approximate 3% difference between their GMI and laboratory A1C results, it’s still important to remember that they’re calculated differently. You’re using the mean glucose values from your CGM to determine the GMI rather than measuring how much sugar is attached to your red blood cells.
If your GMI is always lower than your A1C, your doctor will want to make sure you adjust your target goals accordingly. You might also need to be more vigilant about minimizing the possibility of hypoglycemia.
The study suggested that if your GMI is always higher than your A1C, you should set your laboratory A1C target goal slightly lower to reduce the risk of excessive hyperglycemia.
One of the newer gold standards in diabetes management, particularly those who use CGM technology, is known as Time in Range (TIR). This is because TIR shows how often people are able to stay within the goalposts of their ideal range.
Your GMI can help you get a sense of that.
When you use TIR, you get a better sense of how well you’re keeping your blood sugar levels in your target range. For most people, TIR should be about 70–180 mg/dL, and you want to aim to hit that range approximately 70% of the time. That’s about 17 hours out of a 24-hour day.
This is important because the more you can keep your blood sugar levels in that range, the less likely you are to develop complications. You’ll reduce your risk of developing conditions like diabetic retinopathy or kidney disease.
This table can help you understand more about GMI:
Remember, though: GMI numbers are not the same as A1C and shouldn’t be compared without first discussing the results with your endocrinologist or diabetes care team.
Most importantly, any diabetes number — whether it’s a single glucose reading, a pattern on Time in Range, A1C result, or GMI measurement — is only a piece of information used in managing your diabetes. A number or result doesn’t define you.
Essentially, you use the blood glucose levels from your CGM to come up with your GMI because the calculation uses the number from your mean glucose reading.
And there are some key advantages to using a CGM to get GMI data. For one thing, you don’t have to wait for 3 months to collect enough data to get a GMI.
In fact, the Dexcom G6 manufacturer advises you only need 12 days of CGM data to produce a GMI. A 2018 study found that you can get a good estimate of your CGM metrics over 3 months by using 10 to 14 days of CGM data.
Since you can calculate your GMI using blood sugar readings from a smaller time range, the reading is more accurate and direct.
You do need to have access to CGM to be able to measure your GMI. If you’re in the market for a continuous glucose monitoring system, you have options. Four different models are available as of 2022:
You can talk with your endocrinologist or diabetes care team about which type of product may be your best option.
With advances in technology, you now have more options to help you keep track of your blood sugar levels.
CGM technology can help you learn more about your blood sugar levels, including the immediate impact of the choices that you make and how well you keep your blood glucose levels in your target range over time.
Using both A1C and GMI gives you the information you need to maintain better control over your blood sugar levels and to stay as healthy as possible.
Last medically reviewed on July 14, 2022
Our experts continually monitor the health and wellness space, and we update our articles when new information becomes available.
Current Version
Jul 14, 2022
Jennifer Larson
Edited By
Mike Hoskins
Medically Reviewed By
Kelly Wood, MD
Copy Edited By
Stassi Myer – CE
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