An A1C chart shows the amount of glycated hemoglobin, which is hemoglobin that has excess glucose bound to it, notes the National Institute of Diabetes and Digestive and Kidney Diseases. An A1C level is usually indicated as a percentage; 8 percent is high, while a 5 percent reading is normal.
The A1C test is used in diabetes management, explains the NIDDK. If the amount of sugar entering the bloodstream is consistently high, some of the glucose attaches to the hemoglobin. Because red blood cells have a life span of three months, the A1C test determines the average blood sugar reading over that time period; it is not useful for short-term glucose measurement. Generally, blood glucose levels are deemed normal if A1C levels fall below 5.7 percent, pre-diabetic if above 5.7 and below 6.4 percent, and diabetic if 6.5 percent and above.
While useful in diagnosis, the A1C test has a margin of error of 0.5 percent in each direction, explains the NIDDK. There is also a risk of a false diagnosis if the patient also has anemia or kidney trouble, so doctors need to take their patients' other conditions into account. This test is also not used for women in the third trimester of pregnancy.