Understanding HbA1c and Glycated Hemoglobin
Hemoglobin is the oxygen-carrying protein inside red blood cells. When glucose circulates in your bloodstream, some of it binds irreversibly to hemoglobin molecules—a process called glycation. The resulting compound, HbA1c, represents the percentage of hemoglobin that has bonded with glucose.
Because red blood cells survive approximately 120 days (4 months), HbA1c concentrations directly reflect your average blood glucose over that period. This makes HbA1c fundamentally different from a single glucose reading, which may fluctuate dramatically depending on meals, stress, and physical activity.
Doctors express HbA1c as a percentage. Importantly, HbA1c also has a measurement unit called mmol/mol (milligrams per millimole), sometimes used in countries outside North America. The conversion between these units is non-linear, which is why glucose conversion charts must account for both scales.
How to Convert HbA1c to Estimated Average Glucose
The estimated average glucose formula translates your HbA1c percentage into the average blood sugar concentration (in mg/dL) you would have experienced over the past three months. This conversion was standardised by the American Diabetes Association and is based on population studies correlating HbA1c levels with continuous glucose monitoring data.
eAG (mg/dL) = (28.7 × HbA1c) − 46.7
eAG— Estimated average glucose in milligrams per decilitre (mg/dL)HbA1c— Glycated hemoglobin percentage (%)
Reference Ranges: What Your eAG Means
Non-diabetic individuals:
- HbA1c <5.7% (eAG <140 mg/dL): Normal glucose metabolism, no diabetes risk
- HbA1c 5.7–6.4% (eAG 140–154 mg/dL): Prediabetes range; lifestyle modifications recommended
- HbA1c ≥6.5% (eAG ≥155 mg/dL): Diagnostic threshold for type 2 diabetes
People with diagnosed diabetes:
- HbA1c <6%: Tight control target, typically for pregnant women or those at high hypoglycaemia risk
- HbA1c <7% (eAG <154 mg/dL): Standard management goal for most adults
- HbA1c 7–8% (eAG 154–183 mg/dL): Reasonable target for older adults or those with comorbidities
- HbA1c >9%: Indicates suboptimal control; increased risk of microvascular and macrovascular complications
Key Considerations When Interpreting eAG
Several factors can affect HbA1c accuracy and your eAG interpretation.
- HbA1c reflects averages, not real-time glucose — A single HbA1c value cannot tell you about glucose variability or hypoglycaemic episodes. Two people with identical HbA1c levels may have vastly different glucose patterns. Ask your doctor about continuous glucose monitoring if you experience frequent highs and lows.
- Certain conditions skew HbA1c measurements — Pregnancy, haemolytic anaemia, chronic kidney disease, and transfusions can artificially lower HbA1c even if your true average glucose is higher. Conversely, iron-deficiency anaemia or liver disease may elevate measured HbA1c. Always discuss unusual results with your healthcare provider.
- The conversion formula assumes standard glycation kinetics — The eAG formula works well for most people but may be less accurate at extremely high or low HbA1c values. Individual glucose thresholds vary; some people tolerate higher eAG without complications, whilst others need stricter targets.
- eAG targets depend on individual risk profiles — Age, life expectancy, presence of cardiovascular disease, and hypoglycaemia awareness all influence appropriate target ranges. Aggressive lowering of eAG below 130 mg/dL is not universally beneficial and may increase hypoglycaemia risk in vulnerable groups.
Practical Steps to Improve Your eAG
If your eAG is elevated, evidence-based interventions include:
- Dietary changes: Reduce refined carbohydrates and added sugars; prioritise whole grains, non-starchy vegetables, legumes, and lean proteins. Portion control matters as much as food composition.
- Physical activity: Aim for 150 minutes of moderate-intensity aerobic exercise weekly, plus resistance training 2–3 times per week. Exercise improves insulin sensitivity regardless of weight loss.
- Stress management and sleep: Chronic sleep deprivation and psychological stress elevate cortisol and impair glucose regulation. Prioritise 7–9 hours of sleep and consider mindfulness-based interventions.
- Medication adherence: If prescribed, take antidiabetic medications exactly as instructed. Some medications work better when combined; never adjust doses without guidance.
- Regular monitoring: Request HbA1c testing every 3 months if recently diagnosed or treated, and every 6–12 months once stable. This feedback loop is essential for optimising management.