What is the difference between glucose management indicator and HbA1c?
The glucose management indicator (GMI) and glycated hemoglobin (HbA1c) are used to assess glycemic control in individuals with diabetes. Both measure the percentage of A1c. However, HbA1c measures average levels of up to 3 months [1], while GMI shows estimations based on short-term average glucose values [1]. Additionally, GMI also shows daily fluctuations in glucose levels [2].
What is GMI?
GMI, or Glucose Management Indicator, is a way to estimate the glycation of the hemoglobin in the blood without measuring it. This indicator calculates the A1c hemoglobin based on a formula based on the glucose levels in the blood. GMI is often used with CGM or continuous glucose monitoring systems. It allows us to regularly update the GMI values. The formula to calculate GMI is - GMI (%) = 3.31 + 0.02392*x, where “x” is the glucose levels in the blood [3, 4]. For 150mg/dL of glucose, GMI will be 6.9%, and for 200mg/dL, 8.1%.
Is the GMI accurate?
The difference between the GMI and the HbA1c values is small, but the correlation is moderate. Around 40% of diabetes 2 patients showed an absolute difference of more than 0.5% [5].
Some scientists say that GMI results are of poor quality. Therefore, the mean glucose level should be used to evaluate the short-term glucose levels instead of the GMI estimation [6].
What is A1c?
A1c is also known as Hemoglobin A1c or HbA1c. It is a blood test that measures the glycated percentage of hemoglobin in the blood. The results reflect the average blood sugar level over up to 3 months [7, 8, 9].
The higher the percentage, the higher your blood sugar levels have been.
The A1c test is a diagnostic and monitoring test for diabetes mellitus [10].
A normal A1c level is below 5.7%, prediabetes is between 5.7 and 6.4%, and type 2 diabetes is above 6.5% [10].
What is glycated hemoglobin?
Hemoglobin is a protein found inside red blood cells. These cells live for three months. During this time, glucose enters the blood and binds with hemoglobin in a non-enzymatic reaction. The hemoglobin with a bond glucose molecule is called glycated and can be measured. The A1c test measures the amount of exactly this hemoglobin [8, 9].
Is the A1c accurate?
The A1c test is generally considered accurate, especially in a laboratory. However, A1c test results can be up to 0.5% higher or lower than the actual percentage in the blood [9].
Point-of-care A1c monitors, such as the A1CNow, have shown a good correlation with standardized laboratory tests. However, this method delivers the most accurate results in the range of 6-8% [11]. On the other hand, most over-the-counter kits deliver results in the range of up to 14% of the laboratory results [12].
Nevertheless, in addition to the method's accuracy, some conditions can affect the A1c results. Among them are liver diseases, kidney failure, anemia, blood losses, recent blood transfusions, red blood cell diseases, and pregnancy. Also, some medications like opioids and HIV medication can affect the A1c [7].