Low Hemoglobin A1c (<4%): Causes, Diagnosis, and Management

Causes of Falsely Low HbA1c

Conditions that shorten red blood cell (RBC) lifespan produce falsely low HbA1c because glycation accumulates over the normal 120‑day RBC lifespan. Low HbA1c (<4%) therefore often reflects shortened RBC survival rather than true hypoglycemia. 1, 2
Hemolytic anemia of any etiology lowers HbA1c independent of the assay method used. 1, 2
Glucose‑6‑phosphate dehydrogenase (G6PD) deficiency reduces HbA1c by ≈0.8 % in homozygous men and ≈0.7 % in homozygous women through accelerated RBC turnover. 1
Recent acute blood loss or hemorrhage creates a younger RBC population with less cumulative glycation, resulting in a lower HbA1c. 1
Recent blood transfusion introduces donor RBCs that are younger than the recipient’s native cells, decreasing the average age of circulating RBCs and lowering HbA1c. 1
Erythropoietin therapy stimulates production of new RBCs that have had less time to become glycated, producing a falsely low HbA1c. 1

Repeat the HbA1c measurement in an NGSP‑certified laboratory to rule out analytical error. 1, 2
Use an assay standardized to the DCCT reference method to ensure comparability across laboratories. 1

Peripheral blood smear should be examined for signs of hemolysis (e.g., spherocytes, schistocytes). 2
Hemoglobin electrophoresis is recommended to screen for hemoglobin variants, especially in patients of African descent. 1
G6PD testing is advised in populations with a higher prevalence of the deficiency. 1

Medication review to identify agents that cause hemolysis, stimulate erythropoiesis, or interfere with HbA1c assays (e.g., erythropoietin, certain antiretrovirals). 2

Fasting plasma glucose should be measured to determine the true glycemic status when HbA1c is low. 1

The American Diabetes Association recommends relying on plasma glucose criteria alone for diagnosis and monitoring when conditions affecting RBC turnover are present. 1
Fructosamine or glycated albumin reflect glycemic control over the preceding 2–4 weeks and are not affected by altered RBC lifespan. 2

A marked discordance (e.g., HbA1c < 4 % with fasting glucose > 126 mg/dL) mandates investigation for interfering conditions such as hemolysis or recent transfusion. 1
In patients with hemoglobin variants (e.g., HbSS, HbEE), HbA1c cannot be accurately measured; glycated proteins should be used instead. 2
Iron‑deficiency anemia paradoxically raises HbA1c by prolonging RBC survival, the opposite effect of hemolytic states. 2

African‑American individuals typically have HbA1c values 0.3–0.8 % higher than non‑Hispanic whites at comparable glucose levels.
The X‑linked G6PD G202A variant (present in ~11 % of African Americans) exerts the opposite effect, lowering HbA1c in carriers. 1

The American Diabetes Association recommends considering alternative measures of glycemic control in patients with hemolytic anemias, as A1C may underestimate true glycemic exposure 3, 4, 5, 6
The American Diabetes Association notes that glucose-6-phosphate dehydrogenase (G6PD) deficiency can cause A1C to read falsely low, making it appear better than actual glycemic control 3, 4, 7, 6
Recent blood loss or hemorrhage can cause A1C to underestimate true glycemic exposure, according to the American Diabetes Association 3, 4, 7, 8
The American Diabetes Association recommends using alternative measures of glycemic control in patients with recent blood transfusion, as A1C may be falsely lowered 3, 4, 7, 5, 8
Sickle cell disease can make A1C measurement unreliable, and alternative measures of glycemic control should be used, according to the American Diabetes Association 3, 4, 7, 8
Erythropoietin therapy can cause A1C to read falsely low, making it appear better than actual glycemic control, notes the American Diabetes Association 3, 4, 7, 5, 6, 8
Hemodialysis can cause A1C to underestimate true glycemic exposure, according to the American Diabetes Association 3, 4, 7, 8
End-stage kidney disease can cause A1C to read falsely low, making it appear better than actual glycemic control, notes the American Diabetes Association 5, 6

Acute stress or illness can raise fasting glucose levels, according to the American Diabetes Association 6
Recent carbohydrate restriction can falsely elevate fasting glucose levels, notes the American Diabetes Association 4
Sample handling issues can falsely lower glucose readings, according to the American Diabetes Association 4, 7

The American Diabetes Association recommends using plasma glucose criteria for diagnosis in patients with conditions that affect A1C measurement, such as hemolytic anemias, G6PD deficiency, and recent blood loss or transfusion 3, 4, 7, 6, 8
The American Diabetes Association notes that marked discordance between measured A1C and plasma glucose levels should prompt consideration of using an A1C assay without interference from hemoglobin variants, or switching to plasma glucose criteria for diagnosis and monitoring 3, 4, 7
The American Diabetes Association recommends evaluating for hemoglobin variants or conditions affecting red blood cell turnover in patients with discordant A1C and glucose levels 3, 4, 8

African Americans may have higher A1C levels than non-Hispanic whites with similar glucose levels, independent of hemoglobin variants, according to the American Diabetes Association 3, 4

When A1C seems discordant with clinical picture, the American Diabetes Association recommends obtaining fasting plasma glucose and/or 2-hour oral glucose tolerance test, reviewing complete blood count, and considering hemoglobin electrophoresis if variant suspected 3, 4, 9