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Complete Blood Count
Review status
Currently under review
Pending specialist review and validation.
Hemoglobin A1c is a blood test that reflects your average blood sugar over the past several months. It measures the portion of hemoglobin, the oxygen-carrying protein in red blood cells, that has sugar attached to it.
Because red blood cells circulate for many weeks, this test shows longer-term glucose patterns rather than a single moment in time. It can be drawn at any time of day and usually does not require fasting.
A1c helps you and your care team understand overall glucose control, beyond day-to-day ups and downs. It is used to monitor diabetes, guide changes to nutrition, activity, and medications, and to estimate the risk of eye, kidney, nerve, and heart complications related to long-term high blood sugar.
Clinicians may also order A1c to evaluate for diabetes or prediabetes in people with risk factors or symptoms. It is often checked at regular visits for those with diabetes and can be used alongside home glucose records or sensor data to give a fuller picture.
A higher A1c generally means your average blood sugar has been higher, while a lower A1c suggests closer alignment with your targets. One result is only part of the picture, so your clinician will consider trends, your daily glucose records, and how you feel.
Some conditions can make the result less reliable, including anemia, recent blood loss or transfusion, hemoglobin variants, kidney or liver disease, and pregnancy. If your A1c does not match your meter or sensor readings, ask about repeating the test, verifying the method, or using alternative markers such as fructosamine or glycated albumin.
If your result is outside the expected range for you, discuss next steps. Options may include adjusting medications, nutrition counseling, changes in activity, or checking for factors that affect red blood cells. Together you can decide on a follow-up plan and timing for the next test.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Receiving donor blood or having significant bleeding can change the mix and age of red blood cells, which may make the A1c falsely low or high for a period of time.
Deficiencies that slow red blood cell turnover can increase the average age of cells, sometimes causing A1c to read higher than your true glucose exposure.
Variants like sickle trait or conditions that shorten red cell lifespan can alter A1c results or interfere with some methods. Your lab can use a method validated for common variants.
Chronic kidney or liver disease can affect red blood cell production and survival, which may shift A1c away from what fingersticks or sensors show.
Faster red blood cell turnover and changes in blood volume can make A1c less reflective of current glucose in pregnancy. Other tests may be preferred at certain times.
Drugs that change red cell production or survival, such as erythropoietin, dapsone, antiretrovirals, ribavirin, or high-dose vitamins, can affect A1c accuracy.
Laboratories use different A1c methods. Results should be from a method standardized to reference programs, and the same method is best for tracking over time.
Improper collection tube, labeling errors, or extreme storage conditions can lead to a repeat sample. Let the lab know about recent transfusions or known variants.
References