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also known as glycated hemoglobin or glycosylated hemoglobin,
indicates a patient's blood sugar control over the last two to three
months. A1C is formed when glucose in the blood binds irreversibly
to hemoglobin to form a stable glycated hemoglobin complex. Since
the normal life span of red blood cells is 90-120 days, the A1C will
only be eliminated when the red cells are replaced; A1C values are
directly proportional to the concentration of glucose in the blood
over the full life span of the red blood cells. A1C values are not
subject to the fluctuations that are seen with daily blood glucose
The A1C value is an index of mean blood glucose over the past two to
three months with the majority of that value weighted in the last
thirty days. This bias is due to the body's natural destruction and
replacement of red blood cells. Because red blood cells are constantly
being destroyed and replaced, it does not take 120 days to detect a
clinically meaningful change in A1C following a significant change
in mean blood glucose.
A1c testing poses challenges
for both physicians and patients. Doctors face the difficulty
of managing patients' testing schedules and compliance rates.
Patients must make time every three months to complete these tests,
and then anxiously wait for days to receive their results. An
industry survey of 6,000 diabetic patients found that two-thirds failed
to meet the ADA's A1c target levels. However, researchers
found immediate access and feedback to A1c results created
significant improvements in patients' glucose levels.
The American Diabetes Association (ADA) recommends A1C as the
best test to find out if a patient's blood sugar is under control
over time. The test should be performed every 3 months for
insulin-treated patients, during treatment changes, or when blood
glucose is elevated. For stable patients on oral agents, the
recommended frequency is at least twice per year.