Glycated hemoglobin — measures average blood sugar over 2-3 months by testing how much glucose is attached to hemoglobin.
eAG
Estimated Average Glucose — the average blood sugar level corresponding to a given A1C value, in mg/dL or mmol/L.
Prediabetes
A1C between 5.7-6.4%, indicating higher-than-normal blood sugar that may progress to type 2 diabetes.
Fasting Glucose
Blood sugar measured after 8+ hours of fasting. Normal is below 100 mg/dL.
Glycemic Control
How well blood sugar levels are managed over time, primarily measured by A1C.
Time-in-Range (TIR)
The percentage of time blood glucose stays between 70-180 mg/dL. Higher TIR correlates with better outcomes.
Fructosamine
Glycated serum protein reflecting average glucose over 2-3 weeks. Useful when A1c is unreliable due to hemoglobin variants.
Real-World Examples
Example 1
Well-Controlled Diabetes
A1c: 6.8%, Target: 7.0%
eAG = 148 mg/dL. At ADA target. Estimated ~73% Time-in-Range. Fructosamine ~305.
Example 2
Prediabetes — Lifestyle Intervention
A1c: 6.0%, Target: 5.5%
eAG = 126 mg/dL. Combined diet + exercise could reduce to 4.5-5.2%. The DPP showed 58% risk reduction.
A1C Ranges and What They Mean
A1C Level
Category
Avg Glucose
Action
Below 5.7%
Normal
< 117 mg/dL
Maintain healthy lifestyle
5.7 - 6.4%
Prediabetes
117-137 mg/dL
Lifestyle changes recommended
6.5% or above
Diabetes
> 140 mg/dL
Medical treatment needed
Above 9%
Poorly controlled
> 212 mg/dL
Urgent medical attention
Understanding Your A1C Level
Why A1C Matters
A1C provides a 2-3 month average of blood sugar control, unlike daily finger sticks that only capture a moment in time. It is the gold standard for diabetes management and is strongly correlated with the risk of diabetes complications.
Factors That Affect A1C Accuracy
Certain conditions can skew A1C results: anemia, hemoglobin variants, kidney disease, and recent blood transfusions. People of African, Mediterranean, or Southeast Asian descent may have hemoglobin variants that affect results.
Lowering Your A1C
Each 1% reduction in A1C reduces the risk of microvascular complications by approximately 37%. Regular exercise, balanced diet, medication adherence, and stress management are the pillars of A1C improvement.
Frequently Asked Questions
What is the difference between A1C and daily blood sugar readings?
A1C measures the percentage of hemoglobin proteins in your blood that have glucose attached, reflecting your average blood sugar over the past 2-3 months. Daily finger-stick readings capture a single moment in time and can fluctuate widely based on meals, stress, and activity. A1C gives your doctor a more reliable picture of long-term glucose control.
Can A1C results be inaccurate?
Yes. Conditions that affect red blood cell turnover can skew A1C results. Iron-deficiency anemia, sickle cell trait, thalassemia, recent blood transfusions, and pregnancy can all cause falsely high or low readings. If your A1C doesn't match your daily glucose patterns, ask your doctor about alternative tests like fructosamine or glycated albumin.
What A1C level is considered prediabetic?
An A1C between 5.7% and 6.4% is classified as prediabetes by the American Diabetes Association. This corresponds to an estimated average glucose of roughly 117-137 mg/dL. An A1C of 6.5% or higher on two separate tests is diagnostic for type 2 diabetes. Below 5.7% is considered normal.
How quickly can I lower my A1C?
Because A1C reflects a 2-3 month average, meaningful changes typically take at least 8-12 weeks to appear. Dietary changes, regular exercise, and medication adjustments can produce measurable drops of 0.5-1.5% within one testing cycle. Drastic drops of more than 2% in 3 months should be monitored closely, as rapid glucose normalization can sometimes worsen diabetic retinopathy.
Does the eAG formula work the same for everyone?
The standard ADAG formula (eAG = 28.7 x A1C - 46.7) was derived from a study of approximately 500 adults and provides a population average. Individual variation means your true average glucose could differ from the eAG estimate by up to 15-20 mg/dL. People with higher glycemic variability (big spikes and drops) may find the eAG less representative of their daily experience.