Hemoglobin A1c Test
Medical Revision Author:
Ruchi Mathur, MD
Medical Editor:
William C. Shiel, Jr., MD, FACP, FACR
Introduction
Home blood sugar (glucose) testing
is an important part of controlling blood sugar for diabetics. One important goal of
diabetes
treatment is to keep the blood glucose levels near the normal range of 70 to 120 mg/dl before meals and under 140 mg/dl
at 2 hours after eating. Blood glucose levels are usually tested before and
after meals, and at bedtime. The blood sugar level is typically determined by
pricking a fingertip with a lancing device and applying the blood to a glucose
meter, which reads the value. There are many meters on the market, for example-
Accu-Check Advantage, One Touch Ultra, Sure Step and Freestyle. Each meter has
it's own advantages and disadvantages (some use less blood, some have a larger
digital readout, some take a shorter time to give you results, etc). The test
results are then used to help patients make adjustments in medications, diets,
and physical activities.
Since blood glucose levels can fluctuate widely, even frequent home glucose
testing may not accurately reflect the degree of success in controlling blood
sugar. The hemoglobin A1C test is a valuable measure of the overall
effectiveness of blood glucose control over a period of time.
What is a hemoglobin A1c (A1c)?
To explain what an A1c is, think in simple terms. Sugar sticks, and when it's
around for a long time, it's harder to get it off. In the body, sugar sticks
too, particularly to proteins. The red blood cells that circulate in the body
live for about 3 months before they die off. When sugar sticks to these cells,
it gives us an idea of how much sugar is around for the preceding 3 months. In
most labs, the normal range is 4-5.9 %. In poorly controlled diabetes, its 8.0%
or above, and in well controlled patients it's less than 7.0%. The benefits of
measuring A1c is that is gives a more reasonable view of what's happening over
the course of time (3 months), and the value does not bounce as much as finger
stick blood sugar measurements.
There is a correlation between A1c levels and average blood sugar levels as
follows:
While there are no guidelines to use A1c as a screening tool, it gives a
physician a good idea that someone is diabetic if the value is elevated. Right
now, it is used as a standard tool to determine blood sugar control in patients
known to have diabetes.
| A1c(%) |
Mean blood sugar (mg/dl) |
| 6 |
135 |
| 7 |
170 |
| 8 |
205 |
| 9 |
240 |
| 10 |
275 |
| 11 |
310 |
| 12 |
345 |
The
American Diabetes Association currently recommends an A1c goal of
less than 7.0%.
Of interest, studies have shown that there is a 10% decrease in relative risk
for every 1 % eduction in A1c. So, if a patients starts off with an A1c of 10.7
and drops to 8.2, though there are not yet at goal, they have managed to
decrease their risk of microvascular complications by about 20%. The closer to
normal the A1c, the lower the absolute risk for microvascular complications.
Last Editorial Review: 3/23/2005
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