A1c
HbA1c (glycated hemoglobin) reflects average blood glucose over the past 2-3 months. Key reference points:
- Normal: <5.7%
- Prediabetes: 5.7-6.4%
- Diabetes diagnosis: ≥6.5% (confirmed on repeat)
- Treatment target (most adults with T2DM): <7.0%
- Tighter target (<6.5%): younger patients, short disease duration, no CVD
- Relaxed target (<8.0%): elderly, hypoglycemia-prone, limited life expectancy
How it works: Glucose irreversibly binds to hemoglobin; since RBCs live ~120 days, A1c represents a weighted average of glucose over that period (most recent weeks weighted more heavily).
Limitations:
- Falsely low: hemolytic anemia, blood loss, sickle cell trait, recent transfusion
- Falsely high: iron deficiency anemia, vitamin B12 deficiency, splenectomy
- Not reliable in hemoglobinopathies - use fructosamine instead
Conversion to estimated average glucose (eAG):
eAG (mg/dL) = 28.7 × A1c% - 46.7
Is there a specific aspect you'd like more detail on - interpretation, targets for a specific population, or something else?
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