Blood sugar monitoring provides valuable insights into an individual’s metabolic health. Understanding the various measurements used to assess glucose levels over time is an important step in managing well-being. These measurements offer a comprehensive view of how the body processes sugar, indicating trends rather than single-moment snapshots.
Key Blood Sugar Measurements
Two primary measurements are commonly used to assess blood sugar: average glucose and A1c, also known as glycated hemoglobin or HbA1c. Average glucose refers to the estimated average glucose (eAG), expressed in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L), similar to daily blood glucose readings. This value represents an average of glucose levels over a period.
The A1c test, in contrast, measures the percentage of hemoglobin in red blood cells that has sugar attached to it. Hemoglobin is a protein within red blood cells responsible for carrying oxygen throughout the body. Because red blood cells typically have a lifespan of about two to three months, the A1c test reflects an average of blood sugar levels over this approximate period. A higher percentage indicates that more sugar has been attached to hemoglobin, reflecting higher average blood sugar levels over time.
The Conversion Formula
The relationship between average glucose (eAG) and A1c is well-established through a specific mathematical formula. This formula allows for the conversion between A1c percentage and an estimated average glucose value. The standard formula to calculate estimated average glucose (eAG) in mg/dL from an A1c percentage is: eAG = 28.7 × A1c – 46.7.
To determine the A1c value corresponding to an average glucose of 144 mg/dL, the formula can be rearranged: A1c = (eAG + 46.7) / 28.7. Plugging in 144 mg/dL for eAG, the calculation is (144 + 46.7) / 28.7, which equals 190.7 / 28.7. This calculation yields an A1c result of approximately 6.6%.
What Your A1c Means
An A1c result provides important information about blood sugar control and is a diagnostic tool for prediabetes and diabetes. Different A1c ranges are used to classify an individual’s glucose status.
An A1c level below 5.7% is generally considered normal. A result between 5.7% and 6.4% indicates prediabetes, meaning blood sugar levels are higher than normal but not yet high enough to be diagnosed as diabetes. An A1c of 6.5% or higher, on two separate tests, is used to diagnose diabetes. These classifications help healthcare professionals assess an individual’s risk for developing diabetes or monitor existing conditions.
Influences on Your A1c Result
While A1c primarily reflects average blood sugar levels, various factors beyond glucose control can influence the test result. Conditions that affect red blood cell turnover or the structure of hemoglobin can lead to inaccurate A1c readings. For instance, certain types of anemia, such as iron-deficiency anemia, can cause a falsely elevated A1c. Conversely, recent blood loss or blood transfusions can result in a falsely low A1c due to the presence of younger red blood cells.
Other medical conditions, including kidney failure and liver disease, may also affect A1c accuracy. Some genetic variations in hemoglobin, known as hemoglobin variants, can interfere with certain A1c tests, making results unreliable. Additionally, specific medications, like steroids or certain HIV treatments, and even significant physical or emotional stress, can impact blood sugar levels and, consequently, A1c results.