A blood test currently used as the gold standard for
monitoring people already under care for
diabetes may have far wider use in identifying millions
with undetected diabetes, a team led by a
Johns Hopkins physician suggests.
The hemoglobin A1c test, based on a blood sample, is
widely used to keep tabs on how well
confirmed diabetics keep their blood sugar, or glucose, in
check by showing how much glucose red
blood cells have been exposed to for the past 120 days, the
average lifespan of these cells.
"The test is a measure of long-term glucose control,
but doctors don't typically use it to screen
for or diagnose the disease," said Christopher Saudek,
professor of
endocrinology and metabolism at
the Johns Hopkins University School of Medicine and
director of the Johns
Hopkins Comprehensive Diabetes Center.
"There's reason to believe it could help identify many
of the estimated 6 million people in the
U.S. who have diabetes but don't know it," he said.
The current screening and diagnostic tests measure
only the amount of sugar present at the
moment that blood sample is taken. Consequently, Saudek
says, these tests are accurate only if
patients fast for at least 10 hours before the test because
glucose concentrations can vary greatly
depending on a person's recent meals.
Even then, explains Saudek, the tests miss a
significant portion of people who have diabetes or
are at high risk to develop the disease since glucose also
varies depending on a person's diet and
exercise regimen for several days leading up to the blood
draw.
"If a patient is scheduled for a physical, he or she
may 'tune up' by changing their regimen for a
few days and throw off their test results, causing doctors
to miss the patient's usual pattern of high
blood sugar," he said.
In a consensus statement published in the July
Journal of Clinical Endocrinology and
Metabolism, Saudek and his colleagues conclude that the
HbA1c test should be used as a front-line
method for identifying patients with diabetes, especially
for those at high risk for the disease. Since
the test does not require fasting and isn't affected by
short-term changes in diet and exercise, the
HbA1c test has significant advantages to current testing
methods.
The consensus was reached by a group of
diabetologists, pathologists and internists seeking to
improve detection methods because of the serious
consequences of untreated diabetes for patients
and public health. They met recently in Chicago with
financial support from Metrika, a major
manufacturer of diabetes testing equipment. The panel
deliberations and manuscript preparation were
made independently of the sponsor, according to its
members.
After reviewing relevant published studies and
available tests, the national panel recommended
that individuals who score at least 6 percent on an HbA1c
test may have or be at risk for diabetes and
should be tracked with additional glucose or HbA1c tests.
Those who score between 6.5 percent or
above, if confirmed, should be considered to have
diabetes.
"This is a first step toward changing medical practice
[and] could greatly enhance how well we're
able to identify people with diabetes," Saudek said.
Others who contributed to the consensus statement are
William H. Herman, of the University
of Michigan School of Medicine; David B. Sacks, of Brigham
& Women's Hospital and Harvard Medical
School; Richard M. Bergenstal, of the International
Diabetes Center; David Edelman, of Durham
Veterans Administration Medical Center and Duke University;
and Mayer B. Davidson, of Charles R.
Drew University.
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