[acb-diabetics] debate rafges ove A1C
Patricia LaFrance-Wolf
plawolf at earthlink.net
Sun May 30 17:44:22 GMT 2010
24 May, 2010
and appeared in
Issue 523
Debate Rages on HbA1c for Diabetes Diagnosis
An international expert panel's recommendation last year that glycated
hemoglobin (HbA1c) should be the primary test for diagnosing Type 2 diabetes
has
met considerable resistance, with some researchers and clinicians insisting
that the old standards remain the best....
Advertisement
A point-counterpoint highlighted the continuing controversy over which is
the more accurate and practical way to identify patients with the widely
under-diagnosed
disease: HbA1c or the traditional tests -- fasting plasma glucose and the
oral glucose tolerance test.
The debate at the World Congress on Controversies to Consensus in Diabetes,
Obesity and Hypertension showed that, at least in this area, controversy is
much closer at hand than consensus.
At issue was the
during the American Diabetes Association's annual meeting by a joint
committee of the ADA, the International Diabetes Federation, and the
European Association
for the Study of Diabetes. It called for clinicians to rely on HbA1c instead
of the traditional tests in diagnosing Type 2 diabetes because it gives more
reproducible results and because it's easier to administer for both
clinicians and patients.
Jaakko Tuomilehto, MD, of the University of Helsinki in Finland, presented
the case against HbA1c as a primary diagnostic tool in the debate.
His major points:
Thirty years of clinical experience and research using the traditional tests
will be difficult or impossible to interpret against a new standard.
Although efforts are under way to standardize HbA1c assay methods, many labs
are not in compliance, making the measurement unreliable; point-of-care
tests
are even more variable.
HbA1c levels can vary with patients' ethnicity, smoking status, and other
illnesses such as anemia and hemoglobin defects.
Correlation between HbA1c and the traditional standards is questionable.
HbA1c may not predict risk of some complications, such as coronary artery
disease, as well as the traditional tests can.
Glucose is the toxic agent in diabetes, and therefore it makes sense to
focus on it for making the diagnosis.
He also argued that, because HbA1c lags changes in blood glucose levels,
relying on it will delay diagnoses in many patients. "I think this is the
big issue,"
Tuomilehto said. "We are going in the wrong direction."
Other research presented here supported his position. For example,
researchers showed that, using the recommended HbA1c cutoff of 6.5% as the
standard for
a Type 2 diabetes diagnosis, more than 30% of patients were misdiagnosed.
Joo-Pin Foo, MD, and colleagues, used results from two-hour oral glucose
tolerance testing (OGTT) as the reference standard (199mg/dL.cutoff) in a
sample
of 90 individuals of unknown diabetes status. They found that 20% of those
with HbA1c values of 6.5% or higher failed to meet the OGTT standard.
Another
11% who qualified for a Type 2 diabetes diagnosis by the OGTT results had
HbA1c values below 6.5%.
Women were particularly vulnerable to false-positive results with the HbA1c
test, and there was a trend toward increased false positives among those
with
higher body mass index, Foo and colleagues reported. Older individuals and
men tended to be more prone to false negatives.
"Demographic and metabolic characteristics may have a role in affecting the
accuracy of HbA1c," they concluded.
Tuomilehto made a similar point, suggesting that HbA1c can vary according to
numerous factors that are not yet well understood. The expert panel's
recommendation,
he declared, " is completely premature." He also noted that the World Health
Organization is now reviewing its own position statement on Type 2 diagnosis
management. Its current version, issued in 2006, states that HbA1c is "not
suitable" for diagnostic purposes.
As a member of the committee addressing diagnostic issues, Tuomilehto said
the new document was still being finalized. But he assured attendees that
"HbA1c
is not going to be recommended."
On hand to defend HbA1c-based diagnosis was a member of the expert panel,
Enzo Bonora, MD, PhD, of the University of Verona in Italy. He said when he
first
joined the committee, he was dead-set against the idea. But after seeing the
evidence, he said, "I changed my mind."
Bonora ticked off several rationales for the change:
HbA1c is a better measure of chronic glycemic activity than snapshot
glucose-level testing.
Most diabetic complications are predicted as well by HbA1c compared with the
traditional tests, better in some cases.
HbA1c has lower inherent biological variability compared with fasting plasma
glucose.
HbA1c captures individual susceptibility to glycation, which determines the
risk of complications from a given level of glycemia.
No fasting is required and the results are not affected by stress, recent
exercise, or short-term changes in diet.
Assays for HbA1c are easier to perform, though more costly, and are not
subject to some of the problems associated with glucose measurement.
Bonora argued that results of glucose testing in a research setting may not
translate well to clinical practice. Glucose disappears from blood samples
at
a rate of 5% to 7% per hour because blood contains elements that break it
down.
As a result, if a blood sample is not assayed promptly, falsely low readings
will result. The problem occurs even when blood samples are collected in
tubes
containing anti-glycolytic agents, he said. That and other variability
issues with glucose testing mean that the lack of correlation with HbA1c
does not
necessarily undermine the utility of HbA1c, he suggested.
"There is no gold standard" for diagnosing Type 2 diabetes, Bonora said.
Another problem, he said, is that fasting plasma glucose or OGTT results
must be
confirmed with a second test. This requirement doubles the hassle involved
with these tests for clinicians and patients.
He acknowledged that HbA1c is not reliable under some circumstances, but
noted that, in those cases, the traditional tests are still available.
Practice Pearl
Explain to interested patients that an international panel assembled by the
world's three leading diabetes organizations has recommended that an HbA1c
level
of 6.5% or higher is sufficient to diagnose a person with Type 2 diabetes.
World Congress on Controversies to Consensus in Diabetes, Obesity and
Hypertension; Foo J-P, et al "Demographic and metabolic profile may
influence specificity
of HbA1c in diagnosing diabetes mellitus"
CODHy
2010; Poster 1.
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This article originally posted 24 May, 2010 and appeared in
Issue 523
Debate Rages on HbA1c for Diabetes Diagnosis
An international expert panel's recommendation last year that glycated
hemoglobin (HbA1c) should be the primary test for diagnosing Type 2 diabetes
has
met considerable resistance, with some researchers and clinicians insisting
that the old standards remain the best....
Advertisement
Click here to find out more! frame
Flash movie start
Flash movie end
Click here to find out more! frame end
A point-counterpoint highlighted the continuing controversy over which is
the more accurate and practical way to identify patients with the widely
under-diagnosed
disease: HbA1c or the traditional tests -- fasting plasma glucose and the
oral glucose tolerance test.
The debate at the World Congress on Controversies to Consensus in Diabetes,
Obesity and Hypertension showed that, at least in this area, controversy is
much closer at hand than consensus.
At issue was the
statement issued last June
during the American Diabetes Association's annual meeting by a joint
committee of the ADA, the International Diabetes Federation, and the
European Association
for the Study of Diabetes. It called for clinicians to rely on HbA1c instead
of the traditional tests in diagnosing Type 2 diabetes because it gives more
reproducible results and because it's easier to administer for both
clinicians and patients.
Jaakko Tuomilehto, MD, of the University of Helsinki in Finland, presented
the case against HbA1c as a primary diagnostic tool in the debate.
His major points:
list of 6 items
. Thirty years of clinical experience and research using the traditional
tests will be difficult or impossible to interpret against a new standard.
. Although efforts are under way to standardize HbA1c assay methods, many
labs are not in compliance, making the measurement unreliable; point-of-care
tests
are even more variable.
. HbA1c levels can vary with patients' ethnicity, smoking status, and other
illnesses such as anemia and hemoglobin defects.
. Correlation between HbA1c and the traditional standards is questionable.
. HbA1c may not predict risk of some complications, such as coronary artery
disease, as well as the traditional tests can.
. Glucose is the toxic agent in diabetes, and therefore it makes sense to
focus on it for making the diagnosis.
list end
He also argued that, because HbA1c lags changes in blood glucose levels,
relying on it will delay diagnoses in many patients. "I think this is the
big issue,"
Tuomilehto said. "We are going in the wrong direction."
Other research presented here supported his position. For example,
researchers showed that, using the recommended HbA1c cutoff of 6.5% as the
standard for
a Type 2 diabetes diagnosis, more than 30% of patients were misdiagnosed.
Joo-Pin Foo, MD, and colleagues, used results from two-hour oral glucose
tolerance testing (OGTT) as the reference standard (199mg/dL.cutoff) in a
sample
of 90 individuals of unknown diabetes status. They found that 20% of those
with HbA1c values of 6.5% or higher failed to meet the OGTT standard.
Another
11% who qualified for a Type 2 diabetes diagnosis by the OGTT results had
HbA1c values below 6.5%.
Women were particularly vulnerable to false-positive results with the HbA1c
test, and there was a trend toward increased false positives among those
with
higher body mass index, Foo and colleagues reported. Older individuals and
men tended to be more prone to false negatives.
"Demographic and metabolic characteristics may have a role in affecting the
accuracy of HbA1c," they concluded.
Tuomilehto made a similar point, suggesting that HbA1c can vary according to
numerous factors that are not yet well understood. The expert panel's
recommendation,
he declared, " is completely premature." He also noted that the World Health
Organization is now reviewing its own position statement on Type 2 diagnosis
management. Its current version, issued in 2006, states that HbA1c is "not
suitable" for diagnostic purposes.
As a member of the committee addressing diagnostic issues, Tuomilehto said
the new document was still being finalized. But he assured attendees that
"HbA1c
is not going to be recommended."
On hand to defend HbA1c-based diagnosis was a member of the expert panel,
Enzo Bonora, MD, PhD, of the University of Verona in Italy. He said when he
first
joined the committee, he was dead-set against the idea. But after seeing the
evidence, he said, "I changed my mind."
Bonora ticked off several rationales for the change:
list of 6 items
. HbA1c is a better measure of chronic glycemic activity than snapshot
glucose-level testing.
. Most diabetic complications are predicted as well by HbA1c compared with
the traditional tests, better in some cases.
. HbA1c has lower inherent biological variability compared with fasting
plasma glucose.
. HbA1c captures individual susceptibility to glycation, which determines
the risk of complications from a given level of glycemia.
. No fasting is required and the results are not affected by stress, recent
exercise, or short-term changes in diet.
. Assays for HbA1c are easier to perform, though more costly, and are not
subject to some of the problems associated with glucose measurement.
list end
Bonora argued that results of glucose testing in a research setting may not
translate well to clinical practice. Glucose disappears from blood samples
at
a rate of 5% to 7% per hour because blood contains elements that break it
down.
As a result, if a blood sample is not assayed promptly, falsely low readings
will result. The problem occurs even when blood samples are collected in
tubes
containing anti-glycolytic agents, he said. That and other variability
issues with glucose testing mean that the lack of correlation with HbA1c
does not
necessarily undermine the utility of HbA1c, he suggested.
"There is no gold standard" for diagnosing Type 2 diabetes, Bonora said.
Another problem, he said, is that fasting plasma glucose or OGTT results
must be
confirmed with a second test. This requirement doubles the hassle involved
with these tests for clinicians and patients.
He acknowledged that HbA1c is not reliable under some circumstances, but
noted that, in those cases, the traditional tests are still available.
Practice Pearl
list of 1 items
. Explain to interested patients that an international panel assembled by
the world's three leading diabetes organizations has recommended that an
HbA1c
level of 6.5% or higher is sufficient to diagnose a person with Type 2
diabetes.
list end
World Congress on Controversies to Consensus in Diabetes, Obesity and
Hypertension; Foo J-P, et al "Demographic and metabolic profile may
influence specificity
of HbA1c in diagnosing diabetes mellitus" CODHy 2010; Poster 1.
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