The A1C test is a blood test used to measure the average level of glucose in the blood over the last two to three months, and is used as a means of checking how well blood sugar levels are being controlled for a person with diabetes.ore detail and supporting information is in the body of this article. 1  A1C is an abbreviation for glycated hemoglobin, which forms when glucose attaches to a protein in red blood cells. 2  As blood glucose levels rise, so does the percentage of glycated hemoglobin, so A1C is used to measure diabetes control.
Note: To see if multiple ratios are proportional, you could write them as fractions, reduce them, and compare them. If the reduced fractions are all the same, then you have proportional ratios.
A proportion is an equation with a ratio on each side. It is a statement that two ratios are equal. 3/4 = 6/8 is an example of a proportion. When one of the four numbers in a proportion is unknown, cross products may be used to find the unknown number.