Clinical QuickieEndocrine/Metabolic
A1c vs Serum Glucose
A1c is an average; serum glucose is a moment.
They answer different questions
A1c estimates average glycemia over roughly 2–3 months; serum glucose reflects the current moment and can change rapidly.
Discordance is a clue
Recent steroids, acute illness, anemia, transfusion, CKD, hemoglobin variants and altered RBC turnover can make A1c and glucose disagree.
A 'good' A1c can hide variability
Frequent highs and lows can average into a deceptively acceptable A1c.
Use the right tool for the question
Acute symptoms require current glucose data; long-term control uses A1c plus SMBG/CGM context when appropriate.
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