Hemoglobin A1c

How is it used?

The A1c test is used to monitor the glucose control of diabetics over
time. The goal of those with diabetes is to keep their blood glucose
levels as close to normal as possible. This helps to minimize the
complications caused by chronically elevated glucose levels, such as
progressive damage to body organs like the kidneys, eyes,
cardiovascular system, and nerves. The A1c test result gives a picture
of the average amount of glucose in the blood over the last few
months. This can help the diabetic person and his doctor know if the
measures that are being taken to control his diabetes are successful or
need to be adjusted.

A1c is frequently used to help newly diagnosed diabetics determine
how elevated their uncontrolled blood glucose levels have been over
the last 2-3 months. The test may be ordered several times while
control is being achieved, and then several times a year to verify that
good control is being maintained.

The A1c test may be used to screen for and diagnose diabetes.
However, A1c should not be used for diagnosis of gestational diabetes
in pregnant women or for diagnosis of diabetes in people who have
had recent severe bleeding or blood transfusions, those with chronic
kidney or liver disease , or people with blood disorders such as iron-
deficiency anemia , vitamin B12 deficiency anemia , and some
hemoglobin variants (e.g., patients with sickle cell disease or
thalassemia ). In these cases, a fasting plasma glucose or oral glucose
tolerance test should be used for screening or diagnosing diabetes.
Only A1c tests that have been referenced to an accepted laboratory
method (standardized) should be used for diagnostic or screening
purposes. Currently, point-of-care tests, such as those that may be
used at a doctor's office or a patient's bedside, are not accurate
enough for use in diagnosis but can be used to monitor treatment
(lifestyle and drug therapies).

When is it ordered?

Depending on the type of diabetes that a person has, how well their
diabetes is controlled, and on doctor recommendations, the A1c test
may be measured 2 to 4 times each year. The American Diabetes
Association recommends A1c testing in diabetics at least twice a year.
When someone is first diagnosed with diabetes or if control is not
good, A1c may be ordered more frequently.

For diagnostic and screening purposes, A1c may be ordered as part of
a health checkup or when someone is suspected of having diabetes
because of signs or symptoms of increased blood glucose levels
(hyperglycemia ) such as:

Increased thirst
Increased urination
Fatigue
Blurred vision
Slow-healing infections

What does the test result mean?

For monitoring glucose control, A1c is currently reported as a
percentage and, for most diabetics, it is recommended that they aim to
keep their A1c below 7%. The closer diabetics can keep their A1c to
the American Diabetes Association (ADA)'s therapeutic goal of less
than 7% without experiencing excessive hypoglycemia, the better their
diabetes is in control. As the A1c increases, so does the risk of
complications.

An individual with type 2 diabetes , however, may have an A1c goal
selected by the person and his doctor. The goal may depend on
several factors, such as length of time since diagnosis, the presence
of other diseases as well as diabetes complications (e.g., vision
impairment or loss, kidney damage), risk of complications from low
blood glucose (hypoglycemia), and whether or not the person has a
support system and health care resources readily available. For
example, a person with heart disease who has lived with type 2
diabetes for many years without diabetic complications may have a
higher A1c target (e.g., 7.5%-8.0%) set by their doctor, while someone
who is otherwise healthy and just diagnosed may have a lower target
(e.g., 6.0%-6.5%) as long as low blood sugar is not a significant risk.

The A1c test report also may include the result expressed in SI units
(mmol/mol) and an estimated Average Glucose (eAG), which is a
calculated result based on the A1c levels.
The purpose of reporting eAG is to help a person relate A1c results to
everyday glucose monitoring levels and to laboratory glucose tests.
The formula for eAG converts percentage A1c to units of mg/dL or
mmol/L.
It should be noted that the eAG is still an evaluation of a person's
glucose over the last couple of months. It will not match up exactly to
any one daily glucose test result.

The ADA has adopted this
calculation and provides a calculator and information on the eAG on
their DiabetesPro web site.

In screening and diagnosis, some results that may be seen include:
A nondiabetic person will have an A1c result less than 5.7% (39 mmol/
mol).

Diabetes: A1c level is 6.5% (47 mmol/mol) or higher.
Increased risk of developing diabetes in the future: A1c of 5.7% to 6.4%
(39-46 mmol/mol)

Is there anything else I should know?

The A1c test will not reflect temporary, acute blood glucose increases
or decreases, or good control that has been achieved in the last 3-4
weeks. The glucose swings of someone who has "brittle" diabetes will
also not be reflected in the A1c.
If an individual has a hemoglobin variant , such as sickle cell
hemoglobin (hemoglobin S), they will have a decreased amount of
hemoglobin A. This may limit the usefulness of the A1c test in
diagnosing and/or monitoring this person's diabetes , depending on
the method used.
If a person has anemia , hemolysis , or heavy bleeding, A1c test results
may be falsely low. If someone is iron-deficient, the A1c level may be
increased.
If a person has had a recent blood transfusion, the A1c may be
inaccurate and may not accurately reflect glucose control for 2 to 3
months.

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