Estimated Average Glucose (eAG) From HbA1C

Why Use

Enhances patient-clinician communication by framing the HbA1c in terms that are familiar for patients and comparable to available methods of self-monitoring by glucometer or continuous glucose monitor (CGM).

When to Use

For translating HbA1c results into 3-month average glucose equivalents.

Formula

Pearls / Pitfalls

HbA1c is inaccurate in the setting of hemoglobinopathies or altered red blood cell turnover. HbA1c will be falsely high in untreated anemia, hemoglobin variants, uremia, pregnancy (3 rd trimester). HbA1c will be falsely low in acute blood loss, hemolysis, chronic liver disease, dialysis, transfusions, cystic fibrosis, pregnancy (2 nd trimester). HbA1c reflects a 3-month glucose average, so it does not provide a metric of glucose variability (e.g., hypoglycemia or hyperglycemia episodes) or recent glycemic changes, such as acute illness. However, the 3-month average does factor in postprandial and nocturnal values which may not be captured by intermittent self-monitoring with a glucometer.

Advice

Knowing an estimated average glucose can allow clinicians to share a target for self-monitored glucose levels in terms that are familiar to patients. Always compare HbA1c and available self-monitoring glucose data. While there is some room for individual variation in red blood cell lifespan and glucose uptake, significant discrepancies may require investigation of red blood cell turnover issues. If HbA1c is considered unreliable due to an underlying medical condition, alternative tools for longitudinal glucose surveillance include the glucose management indicator (GMI) on a continuous glucose monitor (CGM), fructosamine, glycated albumin, and 1,5-anhydroglucoitol tests. Consult an endocrinologist for further guidance.