HbA1c to eAG Converter — Estimated Average Glucose

About

Estimated Average Glucose (eAG) is a derived mathematical transformation of the hemoglobin A1c (HbA1c) measurement that expresses glycemic control over the preceding 2–3 months in the same units (mg/dL or mmol/L) that patients see on their daily glucose meters. The concept emerged from the A1c-Derived Average Glucose (ADAG) Study, an international multicenter investigation led by Dr. David M. Nathan at Massachusetts General Hospital, published in Diabetes Care in 2008. The study enrolled 507 participants across 10 centers in the United States, Europe, and Africa, including 268 patients with type 1 diabetes, 159 with type 2 diabetes, and 80 non-diabetic controls. Each participant underwent continuous glucose monitoring (CGM) with at least 2,400 glucose measurements over a 3-month period, and the data were correlated with serial HbA1c measurements. The resulting linear regression equation — eAG (mg/dL) = 28.7 × HbA1c − 46.7 — demonstrated a robust correlation coefficient of 0.92 between measured average glucose and HbA1c. Clinically, eAG is now recommended by the American Diabetes Association (ADA) for routine reporting alongside HbA1c in laboratory reports. It has been endorsed by the American Association of Clinical Endocrinology (AACE) and the International Federation of Clinical Chemistry (IFCC). The eAG is considered an evidence level A recommendation due to the rigorous multicenter validation and consistent replication across diverse populations. The conversion is valid for HbA1c values ranging from 4.0% to 15.0% (20–140 mmol/mol) and is reliable in most patients, though conditions affecting red blood cell turnover — such as hemolytic anemias, hemoglobinopathies (including sickle cell disease and thalassemia), chronic kidney disease, and recent blood transfusions — can alter the relationship between HbA1c and average glucose and should be considered during interpretation.

Formula

eAG (mg/dL) = 28.7 × HbA1c − 46.7 | eAG (mmol/L) = eAG (mg/dL) / 18.018

The ADAG linear regression formula is eAG (mg/dL) = 28.7 × HbA1c (%) − 46.7. For example, an HbA1c of 7% yields eAG = (28.7 × 7) − 46.7 = 200.9 − 46.7 = 154.2 mg/dL. To express the result in mmol/L (the standard unit in many countries outside the United States), divide the mg/dL value by 18.018 (the molecular weight of glucose divided by 10). For the same HbA1c of 7%, eAG in mmol/L = 154.2 ÷ 18.018 ≈ 8.6 mmol/L. The formula is derived from the strong linear relationship between HbA1c and mean plasma glucose observed in the ADAG study, where continuous glucose monitoring data were collected over 3 months and correlated with HbA1c measurements at the end of the monitoring period. The study demonstrated that each 1% change in HbA1c corresponds approximately to a 29 mg/dL (1.6 mmol/L) change in mean glucose. The formula is most accurate in the HbA1c range of 5.0–10.0%, where the linear relationship is strongest, and becomes less precise at extremes of glycemic control. For conversion in reverse — from eAG to HbA1c — the formula can be rearranged: HbA1c = (eAG + 46.7) ÷ 28.7. Clinicians should be aware that eAG represents the arithmetic mean of glucose values over the preceding 2–3 months and does not capture glycemic variability, hypoglycemic episodes, or postprandial excursions. Patients with similar HbA1c values may have very different glucose profiles — one with stable euglycemia and another with wide swings between hypoglycemia and hyperglycemia — yet both will yield the same eAG. Continuous glucose monitoring metrics such as time-in-range (TIR), coefficient of variation (CV), and time above/below range provide complementary information that eAG alone cannot convey.

Score Interpretation

The HbA1c to eAG conversion has transformed how clinicians communicate glycemic control to patients with diabetes. The American Diabetes Association (ADA) Standards of Care (2025) recommend that all laboratory reports include both HbA1c (%) and the calculated eAG (mg/dL or mmol/L) to bridge the gap between the glycated hemoglobin assay and patients' daily glucose monitoring experience. This dual reporting paradigm has been shown to improve patient understanding of their glycemic status, enhance engagement in self-management behaviors, and facilitate shared decision-making about treatment adjustments. The ADA also emphasizes that eAG should be used alongside HbA1c, not as a replacement, since each provides unique information — HbA1c reflects the percentage of glycated hemoglobin, while eAG translates that into an intuitive glucose average. Studies have demonstrated that when patients are informed of their eAG, they are more likely to understand their target range, recognize the impact of lifestyle choices on glucose control, and adhere to monitoring schedules. The International Diabetes Federation (IDF) similarly endorses eAG reporting, particularly in primary care settings where clinicians may find percentage-based HbA1c less intuitive. Beyond patient communication, eAG facilitates comparison with glucose meter downloads and continuous glucose monitoring (CGM) data, enabling clinicians to reconcile laboratory and home monitoring results. The eAG value is also useful in research settings as a standardized outcome measure across studies. However, clinicians must exercise caution in interpreting eAG when conditions that affect red blood cell lifespan are present: hemolytic anemias falsely lower HbA1c (and thus eAG), while iron deficiency anemia, chronic kidney disease, and asplenia can falsely elevate it. In patients with hemoglobin variants such as HbS, HbC, or HbE, certain HbA1c assays may be inaccurate, and the derived eAG will be similarly affected. In such cases, alternative glycemic monitoring methods (CGM, fructosamine, or glycated albumin) are preferred.

Reference Ranges