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HbA1C vs. FBS: The Blood Sugar Puzzle
22 Apr
Summary
- HbA1c reflects average blood sugar over 2-3 months; FBS is a single reading.
- A normal HbA1c with high FBS can indicate occasional spikes, like the dawn phenomenon.
- Consistently high FBS requires attention, even with a good HbA1c, for early glucose imbalance detection.
Conflicting blood sugar test results, such as a low HbA1c with a high fasting blood sugar (FBS), can appear contradictory but are explainable. Dr. Pranav Ghody, an endocrinologist, clarifies that HbA1c measures average glucose over two to three months, while FBS is a snapshot reading. An FBS of 121 mg/dL falls into the prediabetes range and should not be dismissed, even if HbA1c results appear reassuring.
The dawn phenomenon is a common reason for this disparity. This natural hormonal shift in the early morning can elevate blood sugar levels, affecting the FBS reading without significantly impacting the longer-term HbA1c average. Other potential factors include lab variations, poor sleep, stress, late meals, or even illnesses.
Conditions affecting red blood cells, like anemia, can also falsely lower HbA1c. To address such inconsistencies, repeating tests, including post-meal glucose or continuous monitoring, is recommended. Focusing on lifestyle basics like balanced meals, adequate sleep, and stress management is crucial for managing fasting glucose levels.
