How A1c is Calculated

A1C to Estimated Average Glucose (eAG) Calculator

Enter your A1C percentage to calculate your estimated average glucose (eAG) in both mg/dL and mmol/L.

Your Estimated Average Glucose (eAG):

eAG (mg/dL):

eAG (mmol/L):

The A1C test, also known as the hemoglobin A1C, HbA1c, or glycated hemoglobin test, is a crucial blood test used to diagnose and monitor diabetes. Unlike daily blood glucose readings that show your sugar levels at a specific moment, the A1C test provides an average of your blood glucose over the past two to three months. This long-term view is invaluable for understanding how well blood sugar levels are being managed over time.

What is A1C?

Hemoglobin is a protein found in red blood cells that carries oxygen throughout your body. When glucose (sugar) enters your bloodstream, it attaches to hemoglobin. This process is called glycation. The more glucose in your blood, the more it attaches to hemoglobin. The A1C test measures the percentage of your hemoglobin that is coated with sugar.

• Red blood cells live for about three months, which is why the A1C test reflects your average blood sugar levels over that period.
• A higher A1C percentage indicates higher average blood sugar levels, which is associated with a greater risk of diabetes complications.

Why is the A1C Test Important?

The A1C test serves several critical purposes:

1. Diagnosis of Diabetes and Pre-diabetes: It's a primary tool for diagnosing type 2 diabetes and identifying individuals with pre-diabetes, a condition where blood sugar levels are higher than normal but not yet high enough to be classified as diabetes.
2. Monitoring Diabetes Management: For people already diagnosed with diabetes, the A1C test helps healthcare providers assess how well their treatment plan (diet, exercise, medication) is working and make necessary adjustments.
3. Risk Assessment: Consistently high A1C levels indicate a higher risk of developing diabetes-related complications such as heart disease, kidney disease, nerve damage, and vision problems.

How is Estimated Average Glucose (eAG) Calculated from A1C?

While A1C is reported as a percentage, many people find it easier to understand their blood sugar levels in the same units they use for daily monitoring (mg/dL or mmol/L). This is where the concept of Estimated Average Glucose (eAG) comes in. The eAG is a calculated value that converts your A1C percentage into an average blood glucose level, making it more relatable to your daily readings.

The formulas used to calculate eAG from A1C are based on extensive research and are standardized:

• For eAG in mg/dL (milligrams per deciliter):
  eAG (mg/dL) = (28.7 × A1C) - 46.7
• For eAG in mmol/L (millimoles per liter):
  eAG (mmol/L) = (1.59 × A1C) - 2.59

These formulas provide a direct way to understand what your A1C percentage means in terms of your average blood sugar levels over the past few months. Use the calculator above to quickly convert your A1C percentage to eAG.

Example Calculation:

Let's say your A1C test result is 6.5%.

• eAG in mg/dL:
  eAG = (28.7 × 6.5) - 46.7
eAG = 186.55 - 46.7
eAG = 139.85 mg/dL (approximately 140 mg/dL)
• eAG in mmol/L:
  eAG = (1.59 × 6.5) - 2.59
eAG = 10.335 - 2.59
eAG = 7.745 mmol/L (approximately 7.7 mmol/L)

This means an A1C of 6.5% corresponds to an estimated average blood glucose of about 140 mg/dL or 7.7 mmol/L over the past 2-3 months.

What Do A1C Numbers Mean?

Here's a general guide to A1C ranges and what they typically indicate:

• Normal: Below 5.7% (eAG below 117 mg/dL or 6.5 mmol/L)
• Pre-diabetes: 5.7% to 6.4% (eAG 117-137 mg/dL or 6.5-7.6 mmol/L)
• Diabetes: 6.5% or higher (eAG 137 mg/dL or 7.6 mmol/L and above)

For most adults with diabetes, the target A1C is often below 7%. However, individual targets can vary based on age, other health conditions, and duration of diabetes. Always discuss your specific A1C goals with your healthcare provider.

Limitations and Considerations

While the A1C test is highly reliable, certain conditions can affect its accuracy:

• Anemias and Blood Disorders: Conditions like sickle cell anemia, thalassemia, or significant blood loss can affect red blood cell turnover and thus A1C results.
• Kidney or Liver Disease: Severe kidney or liver disease can also impact A1C accuracy.
• Pregnancy: A1C may be less reliable during pregnancy, especially for diagnosing gestational diabetes.
• Recent Blood Transfusions: A recent blood transfusion can dilute the glycated hemoglobin, leading to a falsely low A1C result.

It's important to remember that A1C is an average. It doesn't show daily fluctuations, episodes of hypoglycemia (low blood sugar), or hyperglycemia (high blood sugar). For a complete picture of blood sugar control, A1C is often used in conjunction with daily self-monitoring of blood glucose or continuous glucose monitoring (CGM).

Understanding your A1C and its corresponding eAG is a powerful tool in managing your health. Regular testing and discussions with your doctor are key to maintaining optimal blood sugar control and preventing complications.