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An A1c test is a valuable tool to assess how your diabetes management plan is working. But if you are accustomed to seeing your blood sugar levels represented in mg/dL or mmol/L, A1c test results can be confusing. While an online A1c calculator can seem like a quick way to gain clarity, it isn’t the most reliable choice.

What Is an A1c Test?

An A1c test measures your average blood sugar level over the past two to three months by determining what percentage of hemoglobin has glucose attached to it.

Hemoglobin is a protein molecule in red blood cells that transports oxygen throughout the body. Glucose sticks to this protein, and the more glucose you have in your blood over time, the more it will stick. Because red blood cells live for an average of two to three months, the A1c test is able to capture your average blood sugar over that period of time.

For people living with diabetes, this test (also known as a hemoglobin A1c, HbA1c, or glycated hemoglobin test) is used to evaluate how well blood sugar is being managed. Your healthcare provider will determine what your target should be based on a variety of factors, including age, sex, diabetes type, and health history. They will also determine how often you should be tested.

What Is an A1c Calculator?

An A1c calculator converts an A1c test result (reported as a percentage) to an estimated average glucose value, represented in mg/dL or mmol/L format.

The following chart shows how mg/dL is estimated to correspond to A1c results:

Why Use an A1c Calculator?

Self-monitoring tools such as traditional blood glucose meters (BGMs), continuous blood glucose monitors (CGMs), and automatic blood glucose monitors (ABGMs) report blood sugar in mg/dL or mmol/L, not a percentage. As a result, it can be difficult to understand the relationship between your daily blood sugar levels and your A1c results. An A1c calculator may give you a sense of how your average blood glucose matches up with the individual readings you take.

Drawbacks of Using an Online A1c Calculator

An A1c calculator can help people living with diabetes understand the connection between daily readings and longer-term results. However, such calculators are imperfect and have significant drawbacks.

Online A1c calculators can provide only rough estimations, and sometimes not even that. That’s because A1c tests and daily glucose monitoring are looking at different parameters. While A1c tests assess average blood sugar over time, self-monitoring tools measure blood glucose in the moment and can detect sudden, short-term changes and low blood glucose events. That means your latest BGM reading may not reflect your long-term average blood sugar levels. Additionally, A1c test results can be affected by a number of health conditions, medications, blood loss, pregnancy, and conditions that affect your hemoglobin.

It’s important to remember that an A1c calculator cannot replace an A1c test or daily glucose monitoring, and it should not be used to make treatment decisions.

Getting Clarity

If you have questions about the relationship between your daily blood sugar readings and your A1c test results, talk to your healthcare provider. They can help you understand what your results mean and help you determine if your diabetes management plan would benefit from additional assessment tools, such as time-in-range and points-in-range measurements. Together, you can create strategies that make sense for you.

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