You started taking a GLP-1 medication for weight loss and your provider mentions checking your A1C. Or maybe you saw "A1C" on your lab results and you are not sure what it means or why it matters when you are focused on losing weight, not managing diabetes. Perhaps you have prediabetes and you want to understand whether your medication is helping with blood sugar beyond just the number on the scale.

A1C (also called hemoglobin A1C or HbA1c) is one of the most important blood tests for understanding your metabolic health, and it becomes particularly relevant when taking GLP-1 medications. While these medications are often discussed primarily for weight loss, they have significant effects on blood sugar regulation that show up in A1C measurements. Understanding what A1C measures, what your numbers mean, and how GLP-1 therapy affects this marker helps you see the full picture of what treatment is doing for your health.

This article explains what A1C actually measures and why it matters, what the different A1C ranges mean for diabetes diagnosis and risk, how GLP-1 medications like semaglutide and tirzepatide affect A1C levels based on clinical trial evidence, why some patients and providers choose to monitor A1C during treatment, and what to do if your numbers show concerning patterns.

What A1C Actually Measures

A1C is a blood test that reflects your average blood glucose (blood sugar) levels over the past two to three months. Understanding how this works requires knowing a bit about red blood cells and how glucose behaves in your bloodstream.

Hemoglobin is a protein inside red blood cells that carries oxygen throughout your body. When glucose circulates in your blood, it attaches to hemoglobin molecules. This process is called glycation. Everyone has some glucose attached to their hemoglobin, but people with higher blood sugar levels have more glucose-coated hemoglobin.

Red blood cells live for approximately three months before being replaced. The A1C test measures what percentage of your hemoglobin has glucose attached to it. Because red blood cells are constantly being replaced over a three-month period, the A1C reflects your average blood sugar during that time. A higher percentage means higher average blood sugar. A lower percentage means better blood sugar control.

The A1C is reported as a percentage. For example, an A1C of 5.5% means that 5.5% of your hemoglobin molecules have glucose attached. An A1C of 8% means 8% of your hemoglobin is glycated.

This three-month average is valuable because blood sugar fluctuates constantly throughout the day based on what you eat, your activity level, stress, sleep, and many other factors. A single blood sugar measurement tells you what is happening at one moment in time. The A1C tells you the bigger picture of what your blood sugar has been doing over months.

Understanding A1C Ranges

Medical organizations including the American Diabetes Association (ADA), Centers for Disease Control and Prevention (CDC), and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) have established specific A1C ranges for diagnosing normal blood sugar, prediabetes, and diabetes.

Normal (non-diabetic): An A1C below 5.7% is considered normal. This indicates that your average blood sugar has been in the healthy range over the past three months.

Prediabetes: An A1C between 5.7% and 6.4% indicates prediabetes. This means your blood sugar levels are higher than normal but not yet high enough to be diagnosed as diabetes. Prediabetes increases your risk of developing type 2 diabetes, but it is not inevitable. Lifestyle changes and in some cases medication can help prevent progression to diabetes.

Diabetes: An A1C of 6.5% or higher on two separate tests indicates diabetes. At this level, your average blood sugar has been consistently elevated over months, meeting diagnostic criteria for diabetes.

These ranges serve for diagnosis, but if you already have diabetes, your target A1C will be individualized. The American Diabetes Association recommends that for most adults with diabetes, the A1C goal should be less than 7%. However, targets may be different based on your age, how long you have had diabetes, other health conditions, and risk of low blood sugar episodes.

For people with prediabetes, the higher your A1C within the 5.7% to 6.4% range, the greater your risk of progressing to diabetes. Someone with an A1C of 6.3% has higher risk than someone with an A1C of 5.8%, even though both are in the prediabetes category.

How GLP-1 Medications Affect A1C Levels

GLP-1 receptor agonists like semaglutide and tirzepatide affect blood sugar regulation through several mechanisms, which translate into measurable improvements in A1C for many people taking these medications.

Effects in People With Type 2 Diabetes

Clinical trials provide clear evidence that GLP-1 medications significantly reduce A1C in people with type 2 diabetes. In the STEP 2 trial, which enrolled adults with obesity or overweight and type 2 diabetes, semaglutide 2.4 mg weekly reduced A1C by an average of 1.6 percentage points compared to 0.4 percentage points with placebo over 68 weeks. This represents meaningful improvement in blood sugar control.

The SURMOUNT-2 trial evaluated tirzepatide in adults with obesity or overweight and type 2 diabetes. Participants had a mean baseline A1C of 8.0%. Nearly half (46% to 49%) of participants treated with tirzepatide 10 mg or 15 mg achieved an A1C below 5.7% (normoglycemia, meaning non-diabetic blood sugar levels) by 72 weeks, compared to only 3% of those taking placebo. This demonstrates that tirzepatide not only improves blood sugar control but can help many people with type 2 diabetes achieve blood sugar levels in the normal range.

These A1C improvements occurred without severe hypoglycemia (dangerously low blood sugar) episodes in the trials, which is important because some diabetes medications can cause problematic blood sugar drops.

Effects in People With Prediabetes

For people starting with prediabetes, GLP-1 medications show impressive effects on preventing progression to diabetes and promoting return to normal blood sugar levels. An analysis of participants with prediabetes in the STEP 1, 3, and 4 trials found that 84% to 85% of those taking semaglutide 2.4 mg had normal A1C levels (below 5.7%) at 68 weeks, compared to 48% to 64% of those taking placebo.

This means that for most people with prediabetes who take semaglutide with lifestyle intervention, blood sugar normalizes rather than progressing toward diabetes. This represents a significant metabolic benefit beyond weight loss itself, though the two are related since weight loss improves insulin sensitivity.

Effects in People Without Diabetes

Even in people who start with normal blood sugar levels, GLP-1 medications generally maintain or slightly improve A1C. The STEP 1 trial enrolled adults with obesity or overweight but without diabetes. While A1C was not a primary focus of this trial (since participants did not have diabetes or prediabetes), the medication's effects on glucose metabolism still apply.

The metabolic improvements from GLP-1 therapy (improved insulin sensitivity, better glucose regulation, reduced inflammation) benefit overall health even when starting A1C is already in the normal range.

Why Some Patients and Providers Monitor A1C

It is important to understand that labs are not required to receive GLP-1 medications for weight management. Many patients successfully use these medications without any lab testing. However, some patients and providers find A1C monitoring helpful for specific reasons.

Establishing Baseline for Future Reference

Checking A1C within the first month of starting GLP-1 therapy provides a baseline measurement at the time treatment begins. If you do not currently have insurance coverage for your medication and may need to pursue prior authorization in the future, having a baseline A1C measurement, demonstrating A1C reduction with treatment, and showing maintenance of improved A1C with continued treatment can strengthen prior authorization requests. Insurance companies sometimes require evidence that medication is providing medical benefit beyond just weight loss.

Assessing Metabolic Improvement Beyond Weight

Weight loss is not always linear. You might have weeks where the scale does not move or even goes up slightly despite adherence to treatment. During these plateaus, it can be frustrating when you are not seeing progress on the scale. A1C provides another way to assess whether medication is delivering metabolic benefits. If your A1C has improved significantly even during a weight plateau, this indicates the treatment is working to improve your metabolic health.

For people with prediabetes, watching A1C trend downward toward normal range provides motivation and confirms that you are reducing your diabetes risk. For people with diabetes, seeing A1C improve demonstrates better disease control that reduces risk of long-term complications.

Monitoring for Diabetes Risk

If you have risk factors for diabetes (family history, previous gestational diabetes, PCOS, or other conditions associated with insulin resistance), periodic A1C checking helps catch progression toward diabetes early. While GLP-1 medications generally improve blood sugar control, monitoring confirms this is happening for you individually.

The decision about whether to check A1C should be made collaboratively between you and your provider based on your individual health goals, medical history, and whether the information would be helpful for your care. There is no requirement to check labs, and the choice should be based on shared decision-making about what monitoring makes sense for your situation.

Interpreting Your A1C Results on GLP-1 Therapy

If you and your provider decide to check A1C, understanding what your results mean helps you assess your metabolic health.

If Your A1C Is in the Normal Range (Below 5.7%)

This indicates excellent blood sugar control. If you started treatment with prediabetes or diabetes and your A1C has improved to the normal range, this represents significant metabolic improvement. If you started with normal A1C, maintaining it while losing weight confirms that your blood sugar regulation remains healthy.

If Your A1C Is in the Prediabetes Range (5.7% to 6.4%)

This indicates elevated blood sugar that has not yet reached diabetes levels. If you started with prediabetes and your A1C has decreased within this range (for example, from 6.2% to 5.9%), this represents improvement and reduced diabetes risk even though you are still technically in the prediabetes category.

The goal with prediabetes is generally to move toward the normal range (below 5.7%) or at minimum to prevent progression toward diabetes (6.5% or higher). Most people taking GLP-1 medications with prediabetes at baseline see their A1C improve, often into the normal range, though individual results vary.

If Your A1C Is in the Diabetes Range (6.5% or Higher)

If you have diabetes and started treatment with elevated A1C, the question is whether your A1C is improving with treatment. Most people with diabetes taking GLP-1 medications see meaningful A1C reductions. In clinical trials, average reductions ranged from 1.5 to 2.0 percentage points or more depending on baseline levels and which GLP-1 medication is used.

If your A1C is not improving despite several months on GLP-1 therapy, discuss this with your provider. Possible explanations include needing a higher dose, requiring additional diabetes medications, or needing to reassess lifestyle factors affecting blood sugar.

When to Check A1C and How Often

If you and your provider decide that A1C monitoring would be helpful for your care, the frequency depends on your individual situation and goals.

For people without diabetes or prediabetes who are taking GLP-1 medications purely for weight management, A1C checking is optional. Some patients and providers choose to check it once at baseline and perhaps once or twice during the first year of treatment to confirm metabolic health is stable or improving. Others do not check it at all if there are no concerns about blood sugar regulation.

For people with prediabetes at baseline, checking A1C every six to 12 months while on treatment helps monitor whether blood sugar is normalizing or whether progression toward diabetes is occurring. More frequent checking is generally not needed since A1C reflects a three-month average, so checking more often than every three months provides limited additional information.

For people with type 2 diabetes taking GLP-1 medications, the American Diabetes Association recommends A1C testing at least twice yearly if you are meeting treatment goals with stable control. If your diabetes treatment has changed recently or you are not meeting glycemic targets, testing every three months makes sense until control improves and stabilizes.

The specific monitoring plan should be determined collaboratively with your provider based on your health status and goals. There is no single right answer that applies to everyone.

What to Do If Your A1C Shows Concerning Patterns

If A1C testing reveals unexpected or concerning results, several steps help you respond appropriately.

If A1C Is Rising Despite Treatment

If your A1C increases or fails to improve despite several months on GLP-1 therapy and lifestyle modifications, discuss this with your provider. They may recommend increasing your GLP-1 dose if you are not yet at the maximum, evaluating your diet and physical activity patterns, checking for other conditions affecting blood sugar, or considering whether additional medications might be needed.

For people with diabetes, rising A1C might indicate that GLP-1 therapy alone is insufficient for optimal control and combination therapy might be beneficial.

If A1C Indicates New Diabetes Diagnosis

If you did not previously have diabetes but testing reveals an A1C of 6.5% or higher, this generally requires confirmation with repeat testing on a different day. If confirmed, this represents a new diabetes diagnosis that requires discussion with your provider about treatment modifications, monitoring frequency, and potential need for additional therapies beyond GLP-1 medication.

If A1C Indicates Progression From Prediabetes

If you had prediabetes and your A1C has increased to 6.5% or higher, this indicates progression to diabetes. Your provider should discuss whether your current treatment plan needs adjustment, what additional interventions might help, and how to prevent further progression.

The Bigger Picture: A1C as One Measure of Health

While A1C is valuable for assessing blood sugar control and diabetes risk, it represents only one aspect of your health. Comprehensive assessment includes body weight and body composition, blood pressure, lipid panel (cholesterol and triglycerides), liver and kidney function, and overall quality of life and physical function.

GLP-1 medications typically improve many of these markers simultaneously. Weight loss reduces blood pressure. Metabolic improvements affect cholesterol levels. Reduced inflammation benefits multiple organ systems. A1C is one measure of this broader metabolic improvement, not the only measure that matters.

At Mochi Health, we understand that every person's health journey is unique. Our providers offer personalized treatment plans that consider your complete health picture, not just single numbers. Beyond GLP-1 medications for weight management, we offer comprehensive care including registered dietitian nutritionists, support for related health conditions, and access to a wide range of medications that can support your overall health. You can explore treatment options at https://joinmochi.com/medications.

If you and your provider decide that A1C monitoring would be helpful for your care, this is a choice you make together based on your individual circumstances and goals. Labs are never required for GLP-1 treatment, but they can provide valuable information when monitoring makes sense for your situation.

Check Your Eligibility

If you want to learn whether GLP-1 treatment is right for you and receive personalized guidance from providers who understand comprehensive metabolic health assessment including appropriate use of A1C monitoring, you can start by completing Mochi's eligibility questionnaire. Check your eligibility here: https://app.joinmochi.com/eligibility.

References

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This article is for educational purposes only and should not be considered medical advice. Consult with healthcare providers about whether A1C testing is appropriate for your individual health needs and circumstances.