A glycated hemoglobin (HbA1c) is a preferred screening test for diabetes. Done easily with a fingerstick in your physician’s office, it eliminates the need for fasting (not eating) prior to the test. The diagnosis of diabetes is confirmed if two consecutive A1c levels are greater than or equal to 6.5.
What is the HbA1c?
Red blood cells are permeable to glucose (sugar)—so after they enter your circulation, glucose becomes attached to them. The degree to which your red cells become “sugar coated” depends on your blood glucose level. The A1c indicates the average blood sugar level over the lifespan of the red cell—and it lines up with average blood sugar over the previous 2 – 3 months.
Take home message here: your HbA1c will not be affected if you had pizza the night before, unlike a random blood sugar test. But because the A1c is influenced by the total life cycle of your red cells, the levels can be inaccurate in some folks.
Here are some times the HbA1c will not be helpful:
A1c falsely elevated (HIGH)
Your test may tell you that you have diabetes, but you don’t.
- Untreated anemia from iron deficiency or vitamin B12 and folate deficiency can result in a HbA1c value that is falsely high because your red cell turnover is low. Because you have more “older” red cells instead of making new ones (due to lack of iron, or other vitamins) your HbA1c will be higher than it should be.
- Kidney failure or chronic kidney disease. If you have abnormal kidney function your HbA1c may be falsely high.
- Very high triglycerides (over 1,750) may also cause a falsely elevated HbA1c.
- Splenectomy (spleen surgically removed) will give you a falsely elevated HbA1c, due to decreased red cell turnover. This is because the spleen can’t remove the red cells from the bloodstream—which is the spleen’s normal job.
A1c falsely decreased (LOWER)
Your test may show that you aren’t diabetic, but you are.
- Donating blood or major bleeding. HbA1c levels are likely to be underestimated after blood donation. Donating blood, or major bleeding puts the red blood cells in a hyperkinetic (overactive) state—which shortens the life of the red blood cell.
- Treated iron deficiency anemia or treated vitamin B12 deficiency anemia may lead to a falsely low A1c due to rapid turnover of the red blood cells during treatment. In other words, if you have iron deficiency and are taking iron supplements, your A1c may be falsely low—but if you just have iron deficiency anemia NOT on treatment it will be falsely high.
- Pregnancy. Through the first and second trimester of your pregnancy, the HbA1c may be falsely low due to decreased red blood cell lifespan.
- Vitamin E supplements. If you are taking high doses of vitamin E supplements, your HbA1c may be falsely low due to reduced glycation (less glucose attached to your red blood cells).
- Hemolysis. Folks with hemolysis (red cells being chewed up) have rapid cell turnover and falsely low A1c. Hemolysis from autoimmune diseases, medications (ribavirin, interferon-alpha), or genetic problems like hereditary spherocytosis limits the use of A1c as a diabetes screening test in these folks.
- Erythropoietin treatment (Epogen or Procrit) during chemotherapy or for profound iron deficiency anemia will cause a falsely low HbA1c level, again, due to more rapid cell turnover (more younger red cells).
Your A1c will be inaccurate either way (HIGH or LOW)
- Recent blood transfusion makes the A1c of limited use because transfusion does many things to the measurement, including diluting your red cells with someone else’s red cells. HbA1c results in a recently transfused person should be considered uninterpretable.
Well, what can I be tested with if I can’t do HbA1C?
Fructosamine. Diabetes specialists will check blood concentration of a protein called fructosamine to get a longer-term estimate of your glycemic/sugar control. This gives them a better idea of your sugar levels, over random or fasting blood glucose.