The HbA1c test provides an average blood sugar level over two to three months. Many individuals are more accustomed to understanding their daily blood glucose numbers. Converting the HbA1c percentage into an estimated average glucose (eAG) value can make this long-term average more comprehensible for managing blood sugar levels.
What is HbA1c?
The HbA1c test measures glucose that has attached to hemoglobin in your red blood cells. When glucose enters the bloodstream, it binds to hemoglobin, forming glycated hemoglobin. The more glucose present, the more glycated hemoglobin forms.
Red blood cells live for about two to three months, so the HbA1c test provides an average of blood sugar levels over this period. This offers a broader picture of long-term glucose control compared to a single finger-prick test, which only reflects blood sugar at a particular moment. The HbA1c test is used for diagnosing and monitoring diabetes.
Why Convert HbA1c?
Converting an HbA1c percentage into an estimated average glucose (eAG) value makes the long-term blood sugar average more relatable. HbA1c is reported as a percentage, while daily blood sugar monitoring uses units like milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).
Converting HbA1c to eAG bridges this gap, allowing individuals to see their average blood sugar in the same familiar units as home glucose meters. This helps people understand their glucose control and how lifestyle choices and medical treatments impact their blood sugar. The eAG provides an intuitive representation of the long-term average, facilitating discussions between patients and healthcare providers.
Understanding the Conversion
Estimated Average Glucose (eAG) translates the HbA1c percentage into a value that mirrors daily blood glucose readings. The formula for eAG in milligrams per deciliter (mg/dL) is: eAG (mg/dL) = 28.7 × HbA1c (%) – 46.7. For millimoles per liter (mmol/L), the formula is: eAG (mmol/L) = 1.59 × HbA1c (%) – 2.59.
For example, an HbA1c of 6% converts to approximately 126 mg/dL or 7.0 mmol/L. An HbA1c of 7% corresponds to about 154 mg/dL or 8.6 mmol/L. An HbA1c of 8% is roughly equivalent to 183 mg/dL or 10.1 mmol/L.
Interpreting the Converted Values
For a person without diabetes, a normal eAG is below 114 mg/dL, corresponding to an HbA1c below 5.7%. This range indicates effective blood glucose management and a low risk of diabetes-related complications.
Values indicating pre-diabetes fall within an eAG range of 114 mg/dL to 140 mg/dL, correlating to an HbA1c between 5.7% and 6.4%. This range signals elevated blood sugar not yet high enough for a diabetes diagnosis. An eAG of 140 mg/dL or higher, corresponding to an HbA1c of 6.5% or greater, indicates diabetes. These thresholds identify individuals who may benefit from lifestyle adjustments or medical intervention.
Factors Influencing HbA1c Results
Several factors can influence HbA1c accuracy, potentially making the eAG less representative. Conditions affecting red blood cell lifespan are one factor. For instance, anemias like iron deficiency anemia can falsely elevate HbA1c readings because red blood cells live longer, accumulating more glucose. Conversely, conditions that shorten red blood cell survival, such as hemolytic anemia, sickle cell disease, or significant blood loss, can lead to falsely low HbA1c values.
Kidney disease, particularly in advanced stages or during dialysis, can affect HbA1c accuracy due to altered red blood cell turnover or carbamylated hemoglobin. Recent blood transfusions introduce donor red blood cells, which can temporarily skew results. Certain medications and supplements, including high-dose aspirin, vitamins C and E, or some HIV medications, may also interfere with HbA1c measurements. Discuss any medical conditions or medications with a healthcare provider for accurate interpretation.