21/02/2026
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Various physical conditions, medications, and lifestyle factors can impact the accuracy of an HbA1c test, sometimes causing it to reflect a higher or lower average blood sugar level than is actually present. Because the test measures glucose attached to red blood cells (RBCs) over a 2â3 month lifespan, any factor altering RBC survival or turnover affects the result.
MedlinePlus (.gov)
MedlinePlus (.gov)
+3
Situations Causing Falsely Lowered HbA1c Results
Recent or Heavy Blood Loss: Acute bleeding reduces the number of red blood cells, resulting in a lower reading.
Hemolytic Anemia & Shortened RBC Lifespan: Conditions that destroy red blood cells faster than they are produced reduce the time available for glycation.
Pregnancy: Hormonal changes and increased red blood cell production in the 2nd and 3rd trimesters can significantly lower HbA1c.
Treatment for Anemia/Iron Deficiency: Erythropoietin therapy or treatments for iron/B12 deficiency can lower A1c, sometimes by up to 1.2%.
Splenomegaly: Enlarged spleen can lead to faster destruction of red blood cells.
National Institutes of Health (.gov)
National Institutes of Health (.gov)
+6
Situations Causing Falsely Elevated HbA1c Results
Iron Deficiency Anemia (Without Blood Loss): Reduced red blood cell production leads to older cells circulating longer, allowing more time for glucose to bind, which raises the reading.
Kidney Failure (Chronic Kidney Disease): Uremia (the build-up of waste in the blood) and related anemia can lead to artificially high readings.
Vitamin B12 or Folate Deficiency: These can also extend the lifespan of red blood cells, resulting in a higher A1c.
Alcohol Consumption: Chronic alcohol use can increase A1c.
Splenectomy (Removal of Spleen): Increased RBC lifespan can cause higher levels.
National Institutes of Health (.gov)
National Institutes of Health (.gov)
+3
Other Factors Affecting HbA1c
Blood Transfusions: Recent transfusions can significantly alter results, potentially making them uninterpretable due to the donor blood having a different level of glycated hemoglobin.
Hemoglobin Variants: Genetic variants (e.g., Sickle Cell trait, HbC, HbE) can interfere with the laboratory assay, causing inaccurate readings.
Medications: High-dose Vitamin C and E, opiates, and certain HIV medications may interfere with the test.
Stress: High chronic stress can raise cortisol, which in turn can elevate blood sugar and A1c.
Ethnicity: Some research suggests that ethnicity can affect HbA1c independent of blood glucose levels.
National Institutes of Health (.gov)
National Institutes of Health (.gov)
+8
If a person has any of these conditions, doctors may use alternative methods, such as fructosamine or glycated albumin tests, to measure recent blood sugar control (usually over the past 2â3 weeks).
