Hemoglobin A1C (A1C) is a blood test that measures the percentage of hemoglobin proteins in red blood cells that have glucose attached. Since red blood cells live for about three months, the A1C test provides a long-term view of blood sugar control, representing the average level over the preceding two to three months. Healthcare providers use the term Estimated Average Glucose (eAG) to translate the A1C percentage into milligrams per deciliter (mg/dL), the unit patients use for daily glucose monitoring. This conversion makes the A1C result more understandable for individuals managing pre-diabetes or diabetes.
The Specific Conversion Result
An Estimated Average Glucose (eAG) reading of 148 mg/dL corresponds to an A1C percentage of approximately 6.8%. This conversion is derived from a globally recognized formula that establishes a reliable correlation between the two metrics. The A1C result represents the overall concentration of glucose in the bloodstream across all hours of the day and night for the past few months. Medical professionals rely on this standardized conversion to ensure consistency when discussing blood sugar control with patients. The A1C-derived eAG is considered the official average for clinical assessment.
The Science of the A1C to eAG Relationship
The mathematical relationship between A1C and eAG was established through the A1C-Derived Average Glucose (ADAG) study, a landmark international research project. This study defined the correlation between the percentage of glycated hemoglobin and actual average glucose levels by monitoring subjects over a three-month period. The analysis resulted in the linear regression equation that is now the clinical standard: eAG (mg/dL) = (28.7 A1C) – 46.7. This formula allows clinicians to convert the A1C percentage back into a glucose concentration, such as 148 mg/dL, a unit familiar to patients.
The eAG integrates glucose levels from all periods, including those less frequently measured by patients, such as during sleep or post-meal spikes. The relationship is consistent across different demographics and types of diabetes, making the ADAG formula universally applicable in clinical settings.
What the A1C Categories Mean
A result of 6.8% places the individual into the diagnostic category for diabetes, according to guidelines set by organizations like the American Diabetes Association (ADA). The clinical categories for A1C guide diagnosis and management. An A1C level below 5.7% is considered normal.
The range between 5.7% and 6.4% is classified as pre-diabetes, signifying that blood sugar levels are elevated but not yet high enough for a full diabetes diagnosis. This range indicates an increased risk for developing type 2 diabetes, prompting the need for lifestyle changes and monitoring.
An A1C result of 6.5% or higher is the diagnostic threshold for diabetes. The calculated A1C of 6.8% falls within the diabetic range, suggesting a sustained high average blood sugar level. Careful management is required to mitigate the risk of long-term complications affecting the eyes, kidneys, and nervous system.
While a single test result may be used for diagnosis, a second confirmatory test is often performed to ensure accuracy. The 6.8% result indicates a need for consultation with a healthcare provider to discuss a comprehensive treatment plan. This plan typically includes dietary adjustments, increased physical activity, and potentially medication.