HbA1c Testing Can Find Prediabetes
Jan 8 2011
Measuring glycated hemoglobin levels may be an appropriate means of catching patients with prediabetes, researchers say.
bA1c measurement "should be considered a means of identifying greater numbers of patients at risk for diabetes and heart disease" -- especially because "of its practical nature and wide availability.....The study was limited by its use of cross-sectional data, and it may be lacking in generalizability. For instance, a greater number of African Americans would be identified as having prediabetes than if using fasting plasma glucose or two-hour plasma glucose testing, the researchers noted......HbA1c in a range of 5.5% to 6.5% defines prediabetes and identifies a population with risks for diabetes and heart disease comparable to that defined using results of fasting and two-hour glucose testing.....5.7% -- would identify increased risks of 41.3% for diabetes and 13.3% for heart disease."
HbA1c testing yielded similar probabilities for developing diabetes and heart disease as those estimated by using the 2003 American Diabetes Association definition for prediabetes, Ronald Ackerman, MD, MPH, of Indiana University, and colleagues reported in the January issue of the American Journal of Preventive Medicine.
"The A1c test may provide a badly needed, clinically practical indicator of the composite risk for incident diabetes and cardiovascular disease," they wrote.
* Explain that measuring glycated hemoglobin (HbA1c) levels may be an appropriate means of detecting patients with prediabetes.
* Note that an HbA1c in a range of 5.5% to 6.5% defines prediabetes and identifies a population with risks for diabetes and heart disease comparable to that defined using results of fasting and two-hour glucose testing.
Fasting plasma glucose and two-hour plasma glucose, two commonly used tests for assessing diabetes and prediabetes, are limited because they require a patient to return on a separate day after an overnight fast -- a potential barrier to test completion, the researchers said.
Measuring HbA1c is easier -- it requires only one blood draw. In June 2009, in fact, the International Expert Committee, which represents several major diabetes groups, recommended using HbA1c to diagnose diabetes.
The recommendations of the committee have stirred up some controversy (see article below), still, the researchers said, only about 7% of patients with prediabetes -- who are thus at risk for later diabetes and heart disease -- are aware of their status.
To estimate the risks of developing diabetes and cardiovascular disease for adults with different HbA1c levels, Ackerman and colleagues assessed data from the National Health and Nutrition Examination Survey (NHANES) 2003-2006.
Among adults who met the 2003 ADA definition for prediabetes, the probabilities for developing type 2 disease over 7.5 years and cardiovascular disease over 10 years were 33.5% and 10.7%, respectively.
The researchers found that using HbA1c alone -- with a range of 5.5% to 6.5% defining prediabetes -- would identify a population with comparable risks for diabetes and heart disease (32.4% and 11.4%, respectively).
But using a slightly higher cutoff -- beginning at 5.7% -- would identify increased risks of 41.3% for diabetes and 13.3% for heart disease.
These risks are comparable to those seen in patients enrolled in the Diabetes Prevention Program, which had an enrollment criteria of both elevated fasting plasma glucose and impaired glucose tolerance, the researchers said.
Thus, they concluded, using a bottom cutoff of 5.7% for diagnosing prediabetes may be more appropriate.
Either way, they said, HbA1c measurement "should be considered a means of identifying greater numbers of patients at risk for diabetes and heart disease" -- especially because "of its practical nature and wide availability."
The study was limited by its use of cross-sectional data, and it may be lacking in generalizability. For instance, a greater number of African Americans would be identified as having prediabetes than if using fasting plasma glucose or two-hour plasma glucose testing, the researchers noted.
The study was supported by the CDC and the Robert Wood Johnson Foundation Physician Faculty Scholars Program.
The researchers reported no conflicts of interest.
Primary source: American Journal of Preventive Medicine
Ackerman RT, et al "Identifying adults at high risk for diabetes and cardiovascular disease using hemoglobin A1c" Am J Prev Med 2011; 40(1): 11-17.
HbA1c Not a Sure-Fire Tool for Diabetes Dx
By Kristina Fiore, Staff Writer, MedPage Today
Published: September 30, 2010
Not all physicians are willing to rely on glycated hemoglobin levels alone to diagnose diabetes, despite ADA guidelines.
Although the American Diabetes Association (ADA) recently recommended using it as a diagnostic tool, and the World Health Organization may soon follow, some argue that a cutoff of 6.5% misses too many cases of the disease.
"A definitive cutoff of 6.5% would 'diagnose' a lot of high-risk patients or patients in the prediabetic state as people with normal glycemia," Filip Knop, MD, PhD, head of diabetes research at Gentofte Hospital in Copenhagen, told MedPage Today.
So he suggests that, even for patients with an HbA1c of less than 6.5%, a fasting plasma glucose or two hour oral glucose tolerance test would be in order.
During a session at the European Association for the Study of Diabetes meeting on HbA1c for diagnosis, moderator Jaakko Tuomilehto, MD, PhD, of the University of Helsinki, conducted an audience survey after several presentations suggested the test underdiagnosed diabetes.
When asked how many preferred HbA1c for diagnosis, only a few doctors of the hundreds in attendance raised their hands.
But when Tuomilehto gave them the option of fasting plasma glucose, the vast majority of hands hit the air.
One explanation could be the difference between U.S. and European guidelines. The latter were formed on an evidence base that supports only the use of plasma glucose, Tuomilehto said.
"I have not heard that any European health insurance company accepts A1c as the sole diagnosis of diabetes," he told MedPage Today.
Tuomilehto added that the ADA guidelines were based on recommendations from an expert committee, not scientific evidence.
"While expert opinions are important, they do not form the solid basis that is necessary for evidence-based medicine based on scientific facts scrutinized by commonly agreed scientific standards," he said.
In January 2010, the ADA advocated use of an HbA1c greater than or equal to 6.5% to diagnose diabetes. Historically, the test has been recommended only for monitoring glucose control, while diagnosis was dependent on tests of fasting plasma glucose (126 mg/dL or 7.0 mmol/L) or the two-hour glucose tolerance test (200 mg/dL or 11.1 mmol/L).
There also had been a lack of standardization for the HbA1c assay, an issue that has since been resolved.
Richard Bergenstal, MD, president of the ADA, said there are many advantages to HbA1c over the others. It's more consistent, he said, and isn't susceptible to factors such as whether the patient fasted or was affected by stress.
"I think primary care will love A1c" because of its convenience factor, Bergenstal told MedPage Today.
He added that more of the resistance is coming from specialists.
Knop acknowledges that the test is more reliable than either plasma glucose test, which both "behave with great day-to-day variability. And HbA1c is more convenient for patients."
But he cautions that glycated hemoglobin is generally higher for certain ethnic groups, particularly blacks, as well as older patients, which may lead to misdiagnosis.
And several of the studies presented at the EASD meeting suggested that many patients in high-risk populations who indeed had diabetes were missed by the 6.5% cutoff.
Anemia can also be a confounder as well, and the test is more expensive than its counterparts.
Bergenstal, who practices at the International Diabetes Center at Park Nicollet in Minneapolis, emphasized that the recommendations do not suggest that any one test -- including presentation of clinical symptoms -- is better than the others for diagnosing diabetes.
"Each picks up slightly different patients," Bergenstal said. "All the tests, to me, are good tests for diagnosis."
While that may suggest a combination of these measures would provide the most accurate diagnosis, Tuomilehto said it would be too expensive to use such a battery.
The WHO is mulling all these considerations as it updates its guidelines for diagnosing diabetes. The release date is uncertain, but Bergenstal said it should be relatively soon. Researchers at the EASD meeting expressed frustration with its delay.
Bergenstal noted that WHO has to take into consideration the fact that the HbA1c test may not be available or affordable in all parts of the world.
George Alberti, MD, of Newcastle University in Newcastle upon Tyne, England, and co-chair of the WHO committee working on the revised guidelines, said during a presentation that "glucose tends to be preferred to diagnose diabetes in many situations."
Although an HbA1c of 6.5% or greater can be used to diagnose disease, he said, a value less than that "does not exclude diabetes that may be diagnosed using glucose tests."
He apologized on behalf of the WHO co-chairs "for the uncertainty caused by the delay" in releasing new guidelines.