The A1c is a good test for diagnosing diabetes but could miss some people with early prediabetes, because it is an average. If our plan going forward will be to take care of people early and identify people earlier in the disease and miss less people, this may not be the best test if we want to catch everyone. The oral glucose tolerance test (OGTT) may be the best diagnostic tool, but because of its higher cost and the time involved it most likely will not be used for everyone. Maybe we could relook at the numbers we are using to catch diabetes early and possibly lower the threshold for prediabetes to below 5.7% and have them start to improve their health with better nutrition and physical activity. (1)
The A1c test will not reflect temporary, acute blood glucose increases or decreases. The glucose swings of someone who has “brittle” diabetes will not be reflected in the A1c.
If you have a hemoglobin variant, such as sickle cell hemoglobin (hemoglobin S), you will have a decreased amount of hemoglobin A. This may limit the usefulness of the A1c test in diagnosing and/or monitoring your diabetes. If you have anemia, hemolysis, or heavy bleeding, your test results may be falsely low. If you are iron deficient, you may have an increased A1c measurement. If you have had a recent transfusion, then your A1c will be falsely increased (blood preservative solutions contain high glucose levels) and not accurately reflect your glucose control for 2 to 3 months. (2)