According to the CDC, one in 10 Americans have type 1 or type 2 diabetes. Even more disturbingly, nearly 7.3 million adults (aged 18 years or older) who meet laboratory criteria for diabetes are not aware that they have diabetes, or don’t report having it. It’s important that you get your regular physical, even if you think you’re in good health, because your doctor can catch some early signs that you may be at risk for diabetes and help you develop a plan to prevent disease onset. One of the diagnostic tests your doctor will perform to confirm a diagnosis of diabetes or prediabetes is the HbA1c (or simply, A1c) test. But what is A1c?

This test can not only confirm a diagnosis, but it can be used to read the disease’s trajectory and predict a patient’s risk of microvascular complications. However, it’s not perfect, and there are other tools available to help people with diabetes get a handle on their disease. Here we outline everything you need to know about A1c so you can make the best, educated choices for your health.

Why monitoring blood glucose matters

Monitoring blood glucose levels is one parameter in the management of metabolic health — the collection of five main factors (blood sugar, blood pressure, triglycerides, cholesterol, and waist circumference) that signify overall good health. Poor metabolic health increases your risk for serious diseases such as type 2 diabetes, heart disease and stroke. Concerningly, only 12% of American adults are considered to be in good health, as defined by the following parameters:

• Blood sugar below 100 mg/dL after an overnight fast 
• Blood pressure below 120/80 mm Hg
• Triglycerides below 150 mg/dL
• Waist size less than 40 inches for men and 35 inches for women
• HDL cholesterol (the “good” kind) greater than or equal to 40 mg/dL for men and 50 mg/dL for women

As an important aside, this is particularly concerning given that several researchers have now connected COVID-19 disease severity and death to diabetes. According to the CDC’s Morbidity and Mortality Weekly Report, 40% of Americans who died of COVID-19 in early 2020, when the disease was spreading widely throughout the U.S., had either type 1 or type 2 diabetes. Similarly, a study published in Diabetologia reported that one in 10 diabetic patients hospitalized in early 2020 with COVID-19 died within a week. Untreated diabetes markedly increases COVID-19 severity and complications, but diabetic individuals who have their blood sugar levels under control have had much better outcomes and shorter hospital stays. These outcomes have led experts to recommend that one of the best ways that people with diabetes can lower their risk of getting sick or dying from COVID-19 is to keep their blood sugar levels under control.

What is A1c?

Individuals with diabetes aren’t the only people who could benefit from careful monitoring of blood glucose. You could be prediabetic — at risk for developing diabetes — and not even know it for years. The best way to prevent diabetes and related health complications (such as heart disease and stroke) is to ensure you schedule regular exams with your doctor and catch concerning rises in blood glucose before it’s too late. 

If you might be at risk for prediabetes or type 2 diabetes (T2D), your doctor will conduct an assessment of risk factors; (you can also take your own 60-second risk test on the American Diabetes Association website). Depending on the results of this test, your doctor may then perform additional tests, including an A1c test, which is recommended by the American Diabetes Association (ADA) guidelines as the first way to assess whether a patient might have diabetes or not. 

Hemoglobin is a protein in your blood that carries oxygen to the organs and tissues that need it, and carbon dioxide away from those tissues. But most sugars, including glucose and fructose, spontaneously bond with hemoglobin in the bloodstream in a process called glycosylation. The hemoglobin A1c (A1c for short) test measures nonreversible glycosylation of hemoglobin (expressed as a percentage of total hemoglobin), which is directly related to blood glucose concentrations. 

The test reflects mean blood glucose values over a two- to three-month period, and is not affected by transient spikes or drops in blood glucose levels. A1c is the gold standard for confirming a prediabetes or diabetes diagnosis, and it’s the measure most doctors use to track your progress and diabetes management over time. It can also be used to predict a patient’s risk of microvascular complications (i.e., long-term complications that affect small blood vessels, including retinopathy, nephropathy and neuropathy).

There are three potential results from an A1c test: normal, prediabetic, or diabetic.

• Normal A1c: <5.7%
• Prediabetic A1c: 5.7-6.4%
• Diabetic A1c: >6.4%

How often should I test for A1c?

Periodic testing is recommended for all patients with diabetes, but just how often really depends on each person’s situation and treatment regimen. The ADA recommends the following:

• For patients with stable blood glucose control, twice yearly A1c tests
• For patients with a recent change in therapy or those who are not meeting their glycemic goals, quarterly A1c tests

It’s important to keep in mind that some factors can impact the accuracy of A1c tests. For example, because A1c levels are influenced by rapid red blood cell turnover and blood loss, anemia and hemoglobinopathy could cause inaccurate A1c test results. 

What about other tests?

A1c is a great diagnostic tool, and is good for monitoring patient progress over time, but its utility does have limits. For example, A1c cannot determine hypoglycemic or hyperglycemic episodes — the spikes and dips in blood glucose that can occur throughout the day. It is also not practical for daily management of blood glucose levels. 

Other tests that you might take to assess and control your blood glucose levels include:

• The fasting plasma glucose (FPG) test measures blood glucose levels after an overnight fast, and together with A1c is an early diagnostic measure.

• The glucose tolerance test determines how your body handles glucose after eating and can help confirm the results of A1c and FPG tests.

• The random blood glucose test is a measurement of blood sugar taken at any time during the day.

• Self-monitoring blood glucose (SMBG) tests, which can be performed at home, require finger pricks.

• Continuous glucose monitors (CGMs) are a noninvasive tool that more and more individuals are using for real-time management of their blood glucose levels.

What are CGMs?

Continuous glucose monitors measure interstitial fluid (where your glucose moves after it has been through your blood vessels and capillaries) and so provide a continuous estimate of your blood glucose levels, day and night. CCMs are helpful when you want to understand a more detailed picture of what’s impacting (whether it be food or exercise or sleep) your blood glucose levels, and with the January AI app that pairs with your CGM, you can see in real-time how your blood sugar responds to things like the food you eat and the exercise you do. They attach to the skin in a painless manner and can be worn for weeks at a time. Because of this, they are a great alternative to traditional SMBG tests, which requires finger pricks several times daily.

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CGMs have also proven to be an incredible tool for helping individuals maintain their time in range (TIR) — the amount of time their blood glucose levels are in their target healthy zone. This is important for several reasons:

• Constant spikes throughout the day are not correlated with A1c levels, and they are a serious problem: they can lead to more serious metabolic consequences such as increased insulin resistance.

• CGMs can also quickly detect episodes of hypoglycemia (or catch a downward trend in blood glucose before it turns into hypoglycemia), which can lead to more serious conditions such as seizures or even coma.

• Monitoring postprandial (the clinical term for post-meal) blood glucose (PPG) levels is also important — and easy to do with a CGM. With CGMs, people can even see the specific foods that spike their blood sugar levels and those that don’t, which can help them avoid foods that negatively impact their TIR.

• Many treatment regimens for T2D include a combination of diet and exercise, as physical activity helps lower blood glucose and curb postprandial hyperglycemia. A CGM can help patients, instantly, see how exercise affects their blood glucose, affording them the opportunity of making any necessary adjustments.

Glycemic information isn’t beneficial just for people with diabetes. CGMs, like January AI, can help prediabetic individuals make important diet and exercise adjustments, in real time, to help prevent diabetes from developing. CGM data is complementary to the data gleaned from regular A1c tests, all of which can help your doctor make the most informed decisions regarding your treatment plan, such as changes to your diet, exercise regimen or medication schedule.

Key Takeaways

What is A1c? A1c is the gold standard test for measuring blood glucose levels, in part because it measures mean blood glucose values over a two- to three-month period, unaffected by transient spikes or drops in blood glucose levels. Other tests provide complementary information, including CGMs, which provide a continuous estimate of your blood glucose levels, day and night. CGMs are playing an increasingly important role in helping individuals monitor the impact of daily lifestyle habits (such as meals and exercise) on their blood glucose levels. Real-time management of lifestyle factors can make a significant contribution to an individual’s long-term cardiometabolic and overall health.

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