What’s an A1C Test and Why Might You Need one?

Calvin Wu, MD
November 17, 2021
5 mins

There are many reasons that understanding your blood glucose levels is beneficial — they are a key indicator of health, and they are especially useful in understanding your risk for prediabetes or type 2 diabetes.   

There are several ways to get a comprehensive view of your blood glucose levels — one of the most common being an A1C test. In this post, we’ll take a look at what an A1C test is, what you can expect, and why you might need one. 

What Is an A1C test? 

Hemoglobin is the part of a red blood cell that carries oxygen to the cells. Glucose — commonly referred to as blood sugar — attaches to or binds with hemoglobin in your blood cells.

An A1C test, also called the hemoglobin A1C, HbA1c, glycated hemoglobin, or glycohemoglobin test, measures the amount of glucose that attaches to red blood cells. The higher the glucose levels in your bloodstream are, the more glucose will attach to the hemoglobin. 

Since the average lifespan of a red blood cell is two to three months, the A1C reflects a person’s average glucose levels over that time period.  

The results for an A1C test result are reported as a percentage —  the higher the percentage, the higher your blood glucose levels have been.  

Why Is This Number So Important?

Your healthcare provider can use the A1C test — by itself or in combination with other tests — to diagnose prediabetes and type 2 diabetes. Unlike with many other blood tests, you aren’t required to fast before an A1C test, so you can have the test completed at any time. 

A person without diabetes should have an A1C level below 5.7 percent. A person with prediabetes will have an A1C level between 5.7 and 6.4 percent, and a person with diabetes will have an A1C level greater than 6.5 percent. 

If you don’t have any symptoms of prediabetes or diabetes, but the A1C test shows blood sugar levels within those ranges, the test should be repeated on a different day. 

Why A1C?

Although there are other ways to check for prediabetes or diabetes, most research about diabetes-related complications has been based on A1C testing as a standard measurement. 

A1C testing has been proven to be a useful diagnostic tool for macrovascular complications (coronary artery disease, peripheral arterial disease, and stroke) and microvascular complications (diabetic nephropathy, neuropathy, and retinopathy). 

If you’ve already been diagnosed with prediabetes, the test can help provide insight into what diet and lifestyle changes may prevent diabetes. If you’ve already been diagnosed with diabetes, the test can be used to monitor the disease and help your provider make treatment decisions to prevent diabetes-related complications in the future.

A1C Versus Time-in-Range for Diabetes Management

For people who have already been diagnosed with any form of diabetes, it’s become much easier to get time-in-range data with technology like CGM (continuous glucose monitoring) devices. One limit of A1C testing is that it can’t provide information about daily fluctuations in your blood sugar levels; it can provide only a high-level picture of the beginning and end of your three-month period. When it comes to monitoring blood sugar levels, A1C testing can sometimes miss serious dips and rises in levels if they return to normal at the end of your test. 

Time-in-range is becoming the preferred tracking method for many people, as the information is readily available and you can access it almost any time. An A1C test requires a person to schedule an appointment at a lab to get bloodwork. 

Another benefit of time-in-range is the ability for a provider or patient to select specific time periods and compare them. This means that you can track your food and lifestyle choices (or changes) in real time, to see how they are affecting your blood sugar levels. 

At Carbon Health, our goal is to make sure you have access to the type of care that works for your life. So whether you need an A1C test or are looking for options for CGM devices after your test is completed — we’re here to help. 

Carbon Health provides expert diabetes care. If you’re a California resident, learn more about how a CGM device can help you better manage diabetes from the comfort of home. Schedule a free 15-minute eligibility check.

Carbon Health’s medical content is reviewed and approved by healthcare professionals before it is published, but it is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Talk to your healthcare provider about questions you may have regarding your health or a medical condition, and before making changes to your healthcare routine.





Calvin Wu, MD

Calvin Wu, MD, graduated from the Keck School of Medicine of USC and specialized in endocrinology at Harbor-UCLA Medical Center. He is the director of the Virtual Diabetes Program at Carbon Health.

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