What To Know About A1C and Time in Range

By Melinda Maryniuk, MEd, RD, CDCES

For many years, the A1C has been the gold standard for assessing a person’s glucose levels over time. There is another measure, however, called “time in range” (TIR) that is gaining a lot of attention and it can be confusing to know what each metric refers to and which one a person with diabetes should be focused on. Here’s the bottom line – everyone with diabetes needs to have an A1C blood test. The “time in range” measure is useful to people who wear a CGM, a continuous glucose monitor, and TIR can show potential problems with glucose running too low or too high, even when the A1C is in target.

What is the A1C test – and who needs it?

The A1C (also called hemoglobin A1C or glycosylated hemoglobin) measures the average amount of glucose in the blood over the past 2-3 months. It indicates how well a person’s treatment plan (diabetes medicines, food, activity) is working – and if changes need to be made. An A1C measure is run in your doctor’s office and is usually checked 2-4 times a year.

For most people with diabetes, the goal for the A1C result is 7% or less. For those with prediabetes, the goal is for the A1C to be less than 6.6%. A person without diabetes or prediabetes will have an A1C less than 5.7%. A higher A1C goal is recommended for some people with diabetes, especially those who are older or have been having hypoglycemia often. And a lower A1C goal may be recommended for others. Talk to your healthcare provider to know what A1C goal is right for you. 

If I have an A1C in target range – why do I need to check blood sugar with a meter?

The A1C is a terrific and useful measure, but it doesn’t always show a full picture. Someone could be having blood glucose that runs high – and then low. Even though the overall average blood glucose levels might be right in target (with an A1C of 7%) – it may not reflect some glucose spikes and dips. The goal is to keep blood glucose relatively steady, avoiding the highs and lows. Checking blood glucose with a meter can help show the changes in glucose levels throughout the day.

What is a continuous glucose monitor – and do I need it?

A continuous glucose monitor (CGM) is a device that’s always on your body and measures blood sugar continuously. It includes a sensor (a small device that detects the glucose levels). There are two kinds of CGM. One kind collects information in “real time” (continuously sending glucose values to a receiver). This is sometimes called rtCGM and an example is the Dexcom G6. Another kind is “intermittently scanned” CGM (or is CGM)- where the user will scan the sensor using a special receiver to see the glucose numbers. An example of this kind is the Libre FreeStyle. The first kind a more common with type 1 diabetes as it can alert the wearer immediately if the glucose is going too high or too low. You can either own your CGM, or some medical practices will lend them for a two week period in order to get a two- week snapshot of what your blood glucose levels are doing.

A CGM is often recommended for adults with type 1 diabetes who have an A1C above 7%. It can also be useful for those with type 2 diabetes on intensive insulin therapy (taking insulin before each meal) whose A1C is not in target. And even if you don’t use insulin, it can help identify when glucose levels may be running too high or too low. With this information, it is easier for your doctor to know how to adjust your treatment plan.

What does Time-in-Range (TIR) measure?

Time in Range (TIR) is also a measure of glucose control over time. The term applies to the percent of time that a person spends with their glucose levels in the target range. The range can be individualized for each person – but a general goal is to keep glucose between 70-180 mg/dl at least 70% of the time. This information comes from the data reports that are created from CGM data and is most accurate when it’s based on 14 days of data. The higher the TIR number – the better.

I don’t have a CGM – but I’m curious about my TIR. Can I still measure it?

TIR is a measure that is meant for use with a CGM, as its accuracy depends on a lot of data points. However, if you are curious, and check your blood glucose at least 3 times a day, you can calculate an estimated TIR. For example, ok at all of your blood glucose readings over the past two weeks. Let’s say you check glucose 3 times a day and thus you have a total of 42 readings during two weeks. Write down the number of readings that fall within 70-180. For this example, let’s assume you have 22 readings that fall within range. Two readings fall below 70 and 18 times it falls above 180. To determine your TIR, divide the total number of glucose checks that are in range (22) by the total number of glucose checks (42) and multiply by 100. (22/42 x 100 = TIR) In this case, the TIR is 52%, which is below the target of aiming for glucoses in range at least 70% of the time.

From DiaTribe:

The medical information on Diabetes – What To Know’s website is provided as an information resource only. The content is not in any way intended to be nor should you rely on it as a substitute for professional medical evaluation, diagnosis, advice and treatment.

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