Hemoglobin A1C, also known as HbA1C, is widely touted as the "diabetic truth detector." Measuring the percentage of red blood cells that have been "glycated," or permanently chemically joined to sugar, HbA1C is a good indicator of how well diabetics have kept their blood glucose levels in control over the preceding 90 to 120 days. Sometimes, however, HbA1C can be elevated even in people who do not have diabetes. Here are some of the conditions that are the most common reasons for elevated A1C without diabetes.
- Iron-deficiency anemia. An HbA1C test value (at least as it is usually measured in the United States) is nothing but a percentage. Some red blood cells become "sticky" with glucose even in health people. The percentage is higher for diabetics. However, because A1C is a percentage. It's a ratio of hemoglobin that does have chemical bonds to glucose to hemoglobin that don't. It isn't just changes in blood glucose that can change the ratio. Changes in the production of hemoglobin can change the ratio, too. When there is anemia due to iron deficiency, there is less hemoglobin in all, so the percentage of glycosylated (chemically modified) hemoglobin goes up. Iron-deficiency anemia may raise A1C as much as 1.6 percent.  Iron-deficiency anemia won't raise fasting glucose levels. It won't change a single blood sugar test. But it can change longer-term measurements like HbA1C.  An A1C level of 6.5 percent or higher usually indicates diabetes out of control , but not when there's iron-deficiency anemia. In these cases, the key to lower hemoglobin A1C is treating anemia, not diabetes.
- Extremely high triglyceride levels can interfere with the test for HbA1C so that result is inaccurately high. However, this is a problem primarily when triglycerides are over 1750. 
- Somewhat elevated bilirubin levels are also among the reasons for elevated A1C without diabetes. This can occur with almost any elevated bilirubin number, as low as 21 mg/dl.
- People who have uremia may have high HbA1C even with normal blood glucose levels. 
- Taking vitamin C on a regular basis can result in HbA1C results that are either inaccurately high, when measured by an "electronic" method, or inaccurately low, when measured by an older, wet lab method .
- Deficiencies in folic acid or vitamin B12 reduce red blood cell production and raise HbA1C .
- Lead poisoning elevates A1C levels even when blood sugar levels are normal .
- Alcoholism raises A1C even if blood sugar levels are not elevated .
- Opioid abuse raises HbA1C. . It's among the reasons for elevated A1C without diabetes that doctors tend to overlook.
On the other hand, there are also ways that lower hemoglobin A1C naturally in response to nutritional supplementation. High-dose vitamin E (more than 1000 IU per day) prevents glycosylation, the formation of HbA1C. If you take lots of vitamin E, you can have worse blood sugar control than your A1C test suggests. Pregnancy without anemia can lower A1C, as the mother's body makes more red blood cells, faster, to accommodate the baby. Damage to the spleen can likewise cause inaccurate results in the test.
There are limits to how much these conditions affect your A1C. If you have a hemoglobin A1C result of 20 percent, yes, you have poorly controlled diabetes. Usually, these conditions won't cause your numbers to be off by more than 1 to 2 percent at the very most. However, if you doubt your A1C numbers, there are other tests to determine just how well you are doing with your diabetes:
- Continuous glucose monitoring. In the United States, at least three brands of glucose monitors are generally covered by insurance, the Medtronic CGM, and Dexcom Seven Plus and G4 Platinum. These wearable meters take constant blood glucose measurements for three to seven days. These monitors let diabetics know about highs and lows they might otherwise miss, and they give doctors a good idea of how well diabetes is controlled.
- Fructosamine. This test measures average blood sugar levels over the last two or three weeks, not the last 90 to 120 days. It's another useful measure of diabetes control, but like A1C, it's not perfect. Fructosamine measures how much glucose has been bound to albumin in the blood, not hemoglobin. However, there can be unusually high and unusually low albumin levels, too. Also, fructosamine tests are particularly unreliable for diabetics who take either Tylenol or vitamin C on a regular basis.
- Plasma 1,5-anhydroglucitol (1,5-AG) is a naturally occurring chemical in food. Your kidneys normally keep it in the bloodstream except that they prefer glucose. Higher glucose levels result in lower levels of this chemical. However, if you have kidney disease, your numbers will be erroneously high (which in this case means they indicate you had better diabetes control than you actually did), and in pregnancy, there can be a false low (which means they indicate you had worse diabetes control than you actually did). Also, the test only measures blood glucose levels for the last 48 hours to two weeks.
All of these tests can help explain unexpected changes in A1C, higher or lower A1C values that don't track well to the diabetes numbers you get from daily testing. Only HbA1C, however, can be used to predict diabetic complications, so you will always get an A1C test as part of any diabetes checkup.