The Hemoglobin A1c (A1C) test estimates your average blood glucose level over the preceding two to three months. The test measures the percentage of hemoglobin—the protein in red blood cells that carries oxygen—that has glucose molecules attached, a process called glycation. Since red blood cells typically live for about 120 days, the A1C percentage reflects the long-term glucose environment within your body. An elevated A1C result is often alarming, as it is the primary tool for diagnosing diabetes and prediabetes. However, a high A1C level does not automatically confirm a diabetes diagnosis, as other factors might be at play.
Understanding A1C Diagnostic Ranges
Major health organizations, such as the American Diabetes Association (ADA), established clear A1C thresholds to standardize the diagnosis of abnormal glucose control. These ranges correlate specific A1C percentages with the risk of developing long-term diabetes complications. A result below 5.7% is considered normal. The range between 5.7% and 6.4% is defined as prediabetes, signaling impaired glucose regulation and an increased risk for developing Type 2 Diabetes. A result of 6.5% or higher, confirmed by a repeat test, meets the diagnostic criteria for diabetes. These cut-offs serve as the baseline for diagnosis but do not account for every biological scenario that might impact the test’s accuracy.
Factors That Falsely Elevate A1C Results
Certain medical conditions can artificially inflate the A1C reading without reflecting genuinely high average blood glucose. This occurs when the condition interferes with the normal lifespan or structure of the red blood cells, which are the basis of the test.
- Anemia caused by iron deficiency prolongs red blood cell life, allowing more time for hemoglobin to bind with glucose, leading to a falsely elevated A1C percentage.
- Deficiencies in Vitamin B12 or folate also reduce red blood cell turnover, increasing the calculated A1C value.
- Hemoglobin variants, such as those found in sickle cell trait or thalassemia, are inherited abnormalities that interfere directly with laboratory methods used to measure A1C.
- Conditions causing a prolonged red cell lifespan, such as asplenia (the absence of a functional spleen), also make the A1C an unreliable measure of true average blood sugar.
Other Medical Conditions That Raise A1C
Other non-diabetic conditions can genuinely elevate A1C because they cause actual sustained high blood sugar, known as secondary hyperglycemia. These conditions are not Type 1 or Type 2 Diabetes but create a metabolic environment that mimics it.
Stress, Endocrine Disorders, and Medications
The body’s stress response provides a clear example, as severe physical stress from trauma, major infection, or chronic psychological stress triggers the release of hormones like cortisol. Cortisol raises blood sugar levels, and if this stress is prolonged, the average glucose level and corresponding A1C will rise. Several endocrine disorders directly affect glucose metabolism, such as Cushing’s syndrome, which involves excessive cortisol production. Hypothyroidism is also known to elevate A1C levels, which may decrease once the condition is treated. Furthermore, certain medications induce hyperglycemia as a side effect. High-dose glucocorticoids (steroids) and specific antiretroviral drugs used to treat HIV or medications for hepatitis C can significantly increase blood sugar and A1C.
Chronic Organ Disease
Chronic diseases affecting the body’s regulatory systems can also increase A1C. Advanced Chronic Kidney Disease (CKD) or liver disease, such as non-alcoholic fatty liver disease (NAFLD), impairs the body’s ability to process glucose and insulin effectively. In CKD, the buildup of waste products (uremia) can chemically alter the hemoglobin structure through carbamylation, contributing to an elevated A1C reading.
Necessary Follow-Up Testing
When an elevated A1C result makes a diabetes diagnosis uncertain, follow-up testing is necessary, especially if interference factors are suspected. Alternative tests measure current glucose levels rather than a long-term average. The Fasting Plasma Glucose (FPG) test measures blood sugar after an overnight fast. The Oral Glucose Tolerance Test (OGTT) measures blood glucose two hours after consuming a standardized sugary drink. These tests provide a more immediate snapshot of glucose regulation and are less susceptible to blood cell interference. The fructosamine test, which reflects average glucose over the preceding two to three weeks, may also be used when red blood cell turnover is severely abnormal. Any elevated A1C result should prompt a consultation with a healthcare provider to investigate underlying conditions and accurately interpret the results.