The assessment of long-term blood sugar management relies heavily on two interconnected measurements: the HbA1c test and the estimated Average Glucose (eAG). A1C is a blood test that provides a percentage reflecting the average amount of glucose attached to the hemoglobin protein in red blood cells over the preceding two to three months. The process of glucose attaching to hemoglobin is known as glycation.
The eAG translates this A1C percentage into the same unit of measure used in daily blood sugar checks, typically milligrams per deciliter (mg/dL). This conversion makes the long-term average more relatable for individuals who regularly monitor their glucose levels. These two metrics are mathematically linked to offer a complete picture of blood glucose control over a significant period.
The Direct Conversion of 144 mg/dL
An estimated average glucose (eAG) of 144 mg/dL converts directly to an HbA1c percentage of approximately 6.6%. This figure is derived from an established, standardized mathematical relationship. The conversion formula used by healthcare professionals is A1C = (eAG + 46.7) / 28.7, which provides a reliable approximation of the long-term average.
Applying this formula to an eAG of 144 mg/dL yields an A1C of 6.6%, which is the figure used for reporting purposes. This conversion is reliable because the relationship between the percentage of glycated hemoglobin and the average glucose concentration in the bloodstream is linear. The conversion allows for consistent interpretation of results.
This link helps patients understand their glucose control in units they see daily on their meters, but it represents a single, smoothed average. For comparison, a few other common pairings illustrate this linear relationship: An A1C of 6.0% corresponds to an eAG of 126 mg/dL, 6.5% equals 140 mg/dL, and 7.0% is equivalent to 154 mg/dL.
Interpreting A1C Results Clinically
Knowing that an average glucose of 144 mg/dL corresponds to a 6.6% A1C requires placing this percentage within the clinical framework established by major health organizations. These established thresholds define the categories of glucose control and risk.
Clinical A1C Ranges
- Below 5.7%: Considered normal, indicating healthy long-term blood sugar levels.
- 5.7% to 6.4%: Classified as prediabetes, signaling an elevated risk for developing type 2 diabetes and associated complications.
- 6.5% or higher: The threshold used to diagnose diabetes.
An A1C of 6.6% places an individual into the diagnostic range for diabetes. This level suggests that average blood glucose has been consistently higher than the normal range. Achieving a result in this range typically prompts a healthcare provider to initiate or adjust a treatment plan aimed at lowering the average glucose level.
For most adults with diabetes, the general treatment goal is to maintain an A1C below 7.0% (equivalent to an eAG of 154 mg/dL). Maintaining levels lower than this target is associated with a reduced risk of long-term diabetes-related complications, such as damage to the eyes, kidneys, and nerves. Regular monitoring and adjustment of diet, exercise, and medication are necessary steps to achieve the target A1C.
Why A1C and Average Glucose May Differ
While the A1C test provides a valuable average, it has limitations that can cause its result to differ from daily blood glucose monitoring. The A1C value is a single number that represents an average, meaning it cannot capture daily fluctuations in blood sugar, such as sharp spikes after meals or periods of low blood sugar. Daily glucose meter readings or continuous glucose monitor (CGM) data provide time-specific snapshots that complement the long-term average.
Furthermore, the accuracy of the A1C test depends on the normal lifespan and turnover of red blood cells. Conditions that affect the red blood cells can skew the A1C result, making it an unreliable indicator of true average glucose. For instance, severe anemia, recent significant blood loss, or chronic kidney disease can shorten the life of red blood cells, potentially causing the A1C result to be falsely low.
Conversely, other factors, such as specific hemoglobin variants, can interfere with the laboratory measurement process. Because of these biological variables, healthcare providers consider the A1C alongside daily blood glucose logs and other clinical information when making treatment decisions. The A1C is a long-term indicator, while daily monitoring provides the actionable, moment-to-moment data needed for effective management.