Possible Reasons for Low HbA1c Despite High Blood Sugar

1. Rapid Blood Sugar Spikes (High Variability)

HbA1c measures the average blood sugar over 2-3 months, not instantaneous spikes.

If someone has frequent short-term high sugar spikes but normal sugar most of the time, the HbA1c may remain low.

Example: Someone with fasting blood sugar of 90 mg/dL but post-meal spikes of 250 mg/dL will still have a low HbA1c, even though they experience high blood sugar at times.

2. Shorter Red Blood Cell Lifespan

HbA1c depends on how long red blood cells (RBCs) survive in the bloodstream.

If RBCs die earlier than 120 days, they don’t have enough time to accumulate glucose, leading to a lower HbA1c.

Conditions that reduce RBC lifespan:

• Hemolytic anemia (RBCs break down too quickly)
• Chronic kidney disease
• Liver disease
• Certain medications (e.g., dapsone, ribavirin)

3. Blood Loss (Frequent Bleeding or Blood Donation)

If a person donates blood frequently or has internal bleeding, they lose older, glycated RBCs.

New RBCs replace them, resulting in a lower HbA1c, even if blood sugar is high.

4. Iron Deficiency Anemia (Causes False Low HbA1c)

In iron deficiency, RBC production slows down, and older RBCs stay in the bloodstream longer.

Since these RBCs accumulate more glucose over time, HbA1c might be falsely low.

5. Genetic Variations in Hemoglobin (Hemoglobinopathies)

Certain hemoglobin variants (like sickle cell trait, thalassemia) can lead to incorrect HbA1c readings.

In such cases, fructosamine or continuous glucose monitoring (CGM) is used instead.

Key Takeaway

Yes, it is possible to have a low HbA1c (<5.7%) but still experience high blood sugar levels due to blood sugar variability, shorter RBC lifespan, blood loss, anemia, or hemoglobin disorders.

If there’s a mismatch between HbA1c and actual blood sugar readings, it’s best to check with:

• Fasting & post-meal glucose tests
• Continuous glucose monitoring (CGM)
• Fructosamine test (reflects blood sugar over 2-3 weeks)