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Convert between A1C percentage and estimated average glucose (eAG)
| A1C (%) | eAG (mg/dL) | eAG (mmol/L) | Category |
|---|---|---|---|
| < 5.7 | < 117 | < 6.5 | Normal |
| 5.7 - 6.4 | 117 - 137 | 6.5 - 7.6 | Pre-diabetic |
| ≥ 6.5 | ≥ 140 | ≥ 7.8 | Diabetic |
A1C, also known as HbA1c or glycated hemoglobin, is a blood test that measures your average blood glucose levels over the past 2-3 months. When glucose enters your bloodstream, it attaches to hemoglobin, the protein in red blood cells that carries oxygen. The more glucose in your blood, the more hemoglobin becomes glycated. Since red blood cells live for approximately 3 months, the A1C test provides a long-term view of blood sugar control.
The A1C test is crucial for diagnosing and monitoring diabetes. Unlike daily blood glucose tests that provide a snapshot of current levels, A1C shows how well blood sugar has been controlled over time. An A1C below 5.7% is considered normal, 5.7-6.4% indicates pre-diabetes, and 6.5% or higher on two separate tests indicates diabetes. For people with diabetes, the American Diabetes Association generally recommends an A1C target of less than 7%, though individual targets may vary based on age, health status, and other factors. The estimated average glucose (eAG) translates A1C into the same units (mg/dL or mmol/L) used by daily glucose meters, making it easier to understand and relate to daily readings.
The conversion between A1C and estimated average glucose (eAG) uses a formula derived from the ADAG (A1C-Derived Average Glucose) study, which examined the relationship between A1C and average glucose levels measured by continuous glucose monitoring. To calculate eAG from A1C, use the formula: eAG (mg/dL) = (28.7 × A1C) - 46.7. For example, if your A1C is 6.0%, your eAG would be (28.7 × 6.0) - 46.7 = 126 mg/dL. To convert this to mmol/L, divide by 18.0182, giving you 7.0 mmol/L.
To calculate A1C from average glucose, use the reverse formula: A1C = (eAG + 46.7) / 28.7. If your average glucose over several weeks is 154 mg/dL, your estimated A1C would be (154 + 46.7) / 28.7 = 7.0%. This calculation is particularly useful when you have continuous glucose monitoring data or a large number of self-monitored blood glucose readings and want to estimate what your A1C might be.
It's important to note that eAG is an estimate based on population averages. Individual variation exists, and some people may have A1C values that differ from what their average glucose readings suggest. Factors like anemia, recent blood loss, certain medications, and hemoglobin variants can affect A1C accuracy. Additionally, A1C represents a weighted average that favors more recent glucose levels (the past month more heavily than 2-3 months ago), while eAG calculations assume equal weighting. Always use actual laboratory A1C tests for diagnosis and treatment decisions rather than relying solely on calculated estimates.
This calculator is for educational purposes only. A1C targets vary by individual circumstances. Always consult your healthcare provider for personalized diabetes management goals. Laboratory A1C tests are required for diagnosis; do not use calculated estimates for diagnostic purposes.
If you have diabetes, the American Diabetes Association recommends A1C testing at least twice a year if you're meeting treatment goals, or quarterly if your therapy has changed or you're not meeting goals. People without diabetes should have it checked during routine physical exams, especially if at risk for diabetes.
The general target is below 7% for most adults with diabetes, but this should be individualized. Younger people without complications might aim for 6.5% or lower, while elderly individuals or those with multiple complications might have targets of 7.5-8%. Always discuss your specific target with your healthcare provider.
Yes, A1C represents an average over 2-3 months. You could have occasional high readings but still maintain a normal A1C if your glucose is well-controlled most of the time. Conversely, you might have a high A1C even if some daily readings are normal if you have frequent spikes or consistently elevated levels at certain times.
The eAG-to-A1C formula is based on population averages and may not perfectly match individual results. Factors like hemoglobin variants, anemia, recent blood transfusions, kidney disease, or certain medications can affect A1C. Additionally, if your daily readings are highly variable, the average may not accurately predict A1C.
A1C may be inaccurate in people with certain hemoglobin variants (like sickle cell trait), anemia, recent blood loss or transfusion, pregnancy, chronic kidney disease, or liver disease. Some medications and supplements, particularly those affecting red blood cells, can also impact results. In these cases, alternative tests like fructosamine may be used.
Since A1C reflects 2-3 months of blood sugar control, significant changes typically take at least 2-3 months to appear. However, the test is weighted toward more recent glucose levels, so improvements in the past month will have more impact than older readings. Consistent blood sugar management is key to sustainable A1C reduction.
No. Blood glucose is your sugar level at a specific moment, measured by finger stick or CGM. A1C measures the percentage of hemoglobin that has glucose attached to it, reflecting average glucose over months. They're related but different measurements - think of glucose as weather today, and A1C as the season's climate.
Yes, many CGM systems provide an estimated A1C based on your average glucose from CGM data. This is generally more accurate than estimating from occasional finger sticks because it captures all glucose fluctuations. However, laboratory A1C remains the gold standard for diagnosis and official monitoring.
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